Science and Industry Updates

Drinking water quality standards – MyronLMeters.com

Posted by 26 Feb, 2013

TweetDrinking water quality standards describes the quality parameters set for drinking water. Despite the truism that every human on this planet needs drinking water to survive and that water can contain many harmful compounds, there are no universally recognized and accepted international standards for drinking water. Even where standards exist and are applied, the permitted […]

Drinking water quality standards describes the quality parameters set for drinking water. Despite the truism that every human on this planet needs drinking water to survive and that water can contain many harmful compounds, there are no universally recognized and accepted international standards for drinking water. Even where standards exist and are applied, the permitted concentration of individual constituents may vary by as much as ten times from one set of standards to another.

Many developed countries specify standards to be applied in their own country. In Europe, this includes the European Drinking Water Directive and in the USA the United States Environmental Protection Agency (EPA) establishes standards as required by the Safe Drinking Water Act. For countries without a legislative or administrative framework for such standards, the World Health Organization publishes guidelines on the standards that should be achieved. China adopted its own drinking water standard GB3838-2002 (Type II) enacted by Ministry of Environmental Protection in 2002.

Where drinking water quality standards do exist, most are expressed as guidelines or targets rather than requirements, and very few water standards have any legal basis or are subject to enforcement. Two exceptions are the European Drinking Water Directive and the Safe Drinking Water Act in the USA, which require legal compliance with specific standards.

In Europe, this includes a requirement for member states to enact appropriate local legislation to mandate the directive in each country. Routine inspection and, where required, enforcement is enacted by means of penalties imposed by the European Commission on non-compliant nations.

Countries with guideline values as their standards include Canada which has guideline values for a relatively small suite of parameters, New Zealand where there is a legislative basis but water providers have to make “best efforts” to comply with the standards in Australia.

Range of standards
Although drinking water standards are frequently referred to as if they are simple lists of parametric values, standards documents also specify the sampling location, sampling methods, sampling frequency, analytical methods and laboratory accreditation AQC. In addition, a number of standards documents also require calculation to determine whether a level exceeds the standard, such as taking an average. Some standards give complex, detailed requirements for the statistical treatment of results, temporal and seasonal variations, summation of related parameters, and mathematical treatment of apparently aberrant results.

Parametric values
A parametric value in this context is most commonly the concentration of a substance, e.g. 30 mg/l of Iron. It may also be a count such as 500 E. coli per litre or a statistical value such as the average concentration of copper is 2 mg/l. Many countries not only specify parametric values that may have health impacts but also specify parametric values for a range of constituents that by themselves are unlikely to have any impact on health. These include colour, turbidity, pH and the organoleptic (aesthetic) parameters (taste and odor).

It is possible and technically acceptable to refer to the same parameter in different ways that may appear to suggest a variation in the standard required. For example, nitrite may be measured as nitrite ion or expressed as N. A standard of “Nitrite as N” set at 1.4 mg/l equals a nitrite ion concentration of 4.6 mg/l – an apparent difference of nearly threefold.

Australian standards
Drinking water quality standards in Australia have been developed by the Australian Government National Health and Medical Research Council (NHMRC) in the form of the Australian Drinking Water Guidelines. These guidelines provide contaminant limits (pathogen, aesthetic, organic, inorganic and radiological) as well as guidance on applying limits for the management of drinking water in Australian drinking water treatment and distribution.

European Union standards
The following parametric standards are included in the Drinking Water directive and are expected to be enforced by appropriate legislation in every country in the European Union. Simple parametric values are reproduced here but in many cases the original directive also provides caveats and notes about many of the values given.
• Acrylamide 0.10 μg/l
• Antimony 5.0 μg/l
• Arsenic 10 μg/l
• Benzene 1.0 μg/l
• Benzo(a)pyrene 0.010 μg/l
• Boron 1.0 mg/l
• Bromate 10 μg/l
• Cadmium 5.0 μg/l
• Chromium 50 μg/l
• Copper 2.0 mg/l
• Cyanide 50 μg/l
• 1,2-dichloroethane 3.0 μg/l
• Epichlorohydrin 0.10 μg/l
• Fluoride 1.5 mg/l
• Lead 10 μg/l
• Mercury 1.0 μg/l
• Nickel 20 μg/l
• Nitrate 50 mg/l
• Nitrite 0.50 mg/l
• Pesticides 0.10 μg/l
• Pesticides – Total 0.50 μg/l
• Polycyclic aromatic hydrocarbons 0.10 μg/l Sum of concentrations of specified compounds;
• Selenium 10 μg/l
• Tetrachloroethene and Trichloroethene 10 μg/l Sum of concentrations of specified parameters
• Trihalomethanes — Total 100 μg/l Sum of concentrations of specified compounds
• Vinyl chloride 0.50 μg/l

United States standards
In the USA, the federal legislation controlling drinking water quality is the Safe Drinking Water Act (SDWA) which is implemented by the EPA, mainly through state or territorial primacy agencies. States and territories must implement rules at least as stringent as EPA’s to retain primary enforcement authority (primacy) over drinking water. Many states also apply their own state-specific standards which may be more rigorous or include additional parameters. Standards set by the EPA in the USA are not international standards since they apply to a single country. However, many countries look to the USA for appropriate scientific and public health guidance and may reference or adopt USA standards.

World Health Organisation (WHO) guidelines
The WHO guidelines include the following recommended limits on naturally occurring constituents that may have direct adverse health impact:
• Arsenic 0.010 mg/l
• Barium 10μg/l
• Boron 2400μg/l
• Chromium 50μg/l
• Fluoride 1500μg/l
• Selenium 40μg/l
• Uranium 30μg/l
For man-made pollutants potentially occurring in drinking water, the following standards have been proposed:
• Cadmium 3μg/l
• Mercury 6μg/l For inorganic mercury
Organic species:
• Benzene 10μg/l
• Carbon tetrachloride 4μg/l
• 1,2-Dichlorobenzene 1000μg/l
• 1,4-Dichlorobenzene 300μg/l
• 1,2-Dichloroethane 30μg/l
• 1,2-Dichloroethene 50μg/l
• Dichloromethane 20μg/l
• Di(2-ethylhexyl)phthalate 8 μg/l
• 1,4-Dioxane 50μg/l
• Edetic acid 600μg/l
• Ethylbenzene 300 μg/l
• Hexachlorobutadiene 0.6 μg/l
• Nitrilotriacetic acid 200μg/l
• Pentachlorophenol 9μg/l
• Styrene 20μg/l
• Tetrachloroethene 40μg/l
• Toluene 700μg/l
• Trichloroethene 20μg/l
• Xylenes 500μg/l
Comparison of parameters

The following table provides a comparison of a selection of parameters concentrations listed by WHO, the European Union, EPA and Ministry of Environmental Protection of China.
” indicates that no standard has been identified by editors of this article and ns indicates that no standard exists. μg/l -> Micro grams per litre or 0.001 ppm, mg/L -> 1 ppm or 1000 μg/l (Text made available under the Creative Commons Attribution-ShareAlike License: original found here: http://en.wikipedia.org/wiki/Drinking_water_quality_standards

Parameter

World Health Organization

European Union

United States

China

Acrylamide 0.10 μg/l
Arsenic 10μg/l 10 μg/l 10μg/l 50μg/l
Antimony ns 5.0 μg/l 6.0 μg/l
Barium 700μg/l ns 2 mg/L
Benzene 10μg/l 1.0 μg/l 5 μg/l
Benzo(a)pyrene 0.010 μg/l 0.2 μg/l 0.0028 μg/l
Boron 2.4mg/l 1.0 mg/L
Bromate 10 μg/l 10 μg/l
Cadmium 3 μg/l 5 μg/l 5 μg/l 5 μg/l
Chromium 50μg/l 50 μg/l 0.1 mg/L 50 μg/l (Cr6)
Copper 2.0 mg/l TT 1 mg/l
Cyanide 50 μg/l 0.2 mg/L 50 μg/l
1,2-dichloroethane 3.0 μg/l 5 μg/l
Epichlorohydrin 0.10 μg/l
Fluoride 1.5 mg/l 1.5 mg/l 4 mg/l 1 mg/l
Lead 10 μg/l 15 μg/l 10 μg/l
Mercury 6 μg/l 1 μg/l 2 μg/l 0.05 μg/l
Nickel 20 μg/l
Nitrate 50 mg/l 50 mg/l 10 mg/L (as N) 10 mg/L (as N)
Nitrite 0.50 mg/l 1 mg/L (as N)
Pesticides (individual) 0.10 μg/ l
Pesticides — Total 0.50 μg/l
Polycyclic aromatic hydrocarbons l 0.10 μg/
Selenium 40 μg/l 10 μg/l 50 μg/l 10 μg/l
Tetrachloroethene and Trichloroethene 40μg/l 10 μg/l
Categories : Science and Industry Updates

Recent Papers in Adsorption and Ion Exchange Processes – MyronLMeters.com

Posted by 21 Feb, 2013

TweetContent Table Recent Papers in Adsorption and Ion Exchange Processes Magnetic ion exchange resin treatment for drinking water production Removal of radiocobalt from EDTA-complexes using oxidation and selective ion exchange Ammonium removal from anaerobic digester effluent by ion exchange A hybrid ion exchange-nanofiltration (HIX-NF) process for energy efficient desalination of brackish/seawater Adsorption kinetics and isotherm […]

Content Table

Magnetic ion exchange resin treatment for drinking water production

Journal of Water Supply: Research and Technology—AQUA Vol 58 No 1 pp 41–50 © IWA Publishing 2009 doi:10.2166/aqua.2009.081

Link to Summary Page

B. Sani, E. Basile, L. Rossi and C. Lubello

Department of Civil and Environmental Engineering, University of Florence, Via S. Marta 3, I-50139, Florence, Italy Tel.: +39 55 479 6317 E-mail: beatrice.sani@dicea.unifi.it
Publiacqua SpA, Via Villamagna 39, I-50126, Florence, Italy

Abstract

Italian drinking water treatment plants (DWTP) generally use chlorine-based chemicals to achieve the oxidation/disinfection phases of their treatment trains. The main problem related to the application of such disinfectants consists in the formation of disinfection by-products (DBPs) as a result of the reaction with organic substances in the water. Italian regulations set very strict limits for the maximum concentration of chlorine DBPs and, for many DWTPs, the compliance with such a regulation is difficult. Non-oxidative pre-treatments, able to remove organic substances from the water prior to chlorination, could be a suitable solution to overcome this problem. These treatments could increase the water quality, decrease the oxidant demand and, hence, reduce the formation of DBPs. This paper presents an experimental investigation of ion exchange processes for the dissolved organic carbon (DOC) removal by using MIEX® resin. The process was studied as a pre-treatment on raw river water. The DOC removal efficiency and the effects on downstream processes of the treatment train were evaluated.

Removal of radiocobalt from EDTA-complexes using oxidation and selective ion exchange

Water Science & Technology—WST Vol 60 No 4 pp 1097–1101 © IWA Publishing 2009 doi:10.2166/wst.2009.458

org.xwiki.gwt.dom.client.Element#placeholderhttp://www.iwaponline.com/wst/06004/wst060041097.htm“>Link to Summary Page

L. K. Malinen, R. Koivula and R. Harjula

Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55 (A. I. Virtasen aukio 1), FI-00014, Finland E-mail: leena.k.malinen@helsinki.fi; risto.koivula@helsinki.fi; risto.harjula@helsinki.fi

Abstract

Methods for the removal of radiocobalt from an ethylenediaminetetraacetic acid (EDTA) complex of Co(II) (aqueous solution containing 10 mM Co(II) and 10 mM or 50 mM EDTA traced with 57Co) are presented. The studies examined a combination of different oxidation methods and the sorption of 57Co on a selective inorganic ion exchange material, CoTreat. The oxidation methods used were ultraviolet (UV) irradiation with and without hydrogen peroxide (H2O2), as well as ozonation alone or in combination with UV irradiation. Also, the possible contribution of Degussa P25 TiO2 photocatalyst to degradation of EDTA was studied. The best results for the equimolar solution of Co(II) and EDTA were achieved by combining ozonation, UV irradiation, Degussa P25 TiO2 and CoTreat, with approximately 94% sorption of 57Co. High values for the 57Co sorption were also achieved by ozonation (~88%) and UV irradiation (~90%) in the presence of CoTreat and Degussa P25 TiO2. A surplus of EDTA over Co(II) was also tested using 10 mM Co(II) and 50mM EDTA. Only a slight decrease, to ~88% sorption of 57Co, was detected compared to the value (~90%) obtained with 10 mM EDTA.

Ammonium removal from anaerobic digester effluent by ion exchange

Water Science & Technology—WST Vol 60 No 1 pp 201–210 © IWA Publishing 2009 doi:10.2166/wst.2009.317

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T. Wirthensohn, F. Waeger, L. Jelinek and W. Fuchs

Department of IFA-Tulln, Institute for Environmental Biotechnology, University of Natural Resources and Applied Life Sciences—Vienna, Konrad Lorenz Strasse 20, 3430 Tulln, Austria E-mail: thomas.wirthensohn@boku.ac.at; frank.waeger@boku.ac.at; werner.fuchs@boku.ac.at
Department of Power Engineering, Faculty of Environmental Technology, Institute of Chemical Technology, Technicka 5, 166 28 Prague 6, Czech Republic E-mail: Ludek.Jelinek@vscht.cz

Abstract

The effluent of a 500 kW biogas plant is treated with a solid separation, a micro filtration and a reverse osmosis to achieve nutrient recovery and an effluent quality which should meet disposal quality into public water bodies. After the reverse osmosis, the ammonium concentration is still high (NH4-N = 467 mg/l), amongst other cations (K+=85 mg/l; Na+=67 mg/l; Mg2 + =0.74 mg/l; Ca2 + =1.79 mg/l). The aim of this study was to remove this ammonium by ion exchange. Acidic gel cation exchange resins and clinoptilolite were tested in column experiments to evaluate their capacity, flow rates and pH. Amberjet 1,500 H was the most efficient resin, 57 BV of the substrate could be treated, 1.97 mol NH4-N/l resin were removed. The ammonium removal was more than 99% and the quality of the effluent was very satisfactory (NH4-N < 2 mg/l). The breakthrough of the observed parameters happened suddenly, the order was sodium—pH—ammonium—potassium. The sharp increase of the pH facilitates the online control, while the change in conductivity is less significant. A regeneration with 3 bed volumes of 2  M HCl recovered 91.7% of the original cation exchange capacity.

A hybrid ion exchange-nanofiltration (HIX-NF) process for energy efficient desalination of brackish/seawater

Water Science & Technology: Water Supply—WSTWS Vol 9 No 4 pp 369–377 © IWA Publishing 2009 doi:10.2166/ws.2009.634

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S. Sarkar and A. K. SenGupta

Department of Civil and Environmental Engineering, Lehigh University, Fritz Engineering Laboratory, 13 E Packer Avenue, Bethlehem PA, 18015, USA E-mail: sus9@lehigh.edu;arup.sengupta@lehigh.edu

Abstract

This study reports a new hybrid ion exchange-nanofiltration (HIX-NF) process for desalination of sea and brackish water that can attain significant energy economy over the conventional membrane-based pressure driven processes. In this hybrid process, an ion exchange step converts monovalent chloride ions of saline water to divalent sulfate ions and the resulting solution, having a reduced osmotic pressure than the feed, is desalinated using a nanofiltration (NF) membrane. The sulfate rich reject stream from the NF process is used to regenerate the anion exchanger. Results validate that NF membranes can desalinate sodium sulfate solution at a much lower transmembrane pressure compared to RO membranes as well as yield a higher permeate flux. The sulfate-chloride selectivity of the anion exchangers plays important role in sustainability of the process. Laboratory studies have revealed that a single type of anion exchanger cannot sustain the process for saline water with different salt concentrations. However, anion exchangers with different sizes of amine functional groups (e.g. quaternary-, tertiary-, secondary- and primary amine) hold the promise that the process can be tailored to achieve sustainability. Laboratory studies have validated the basic premise of the hybrid process including greater than two times less energy requirement than RO process for the same feed water and same permeate recovery condition.

Adsorption kinetics and isotherm characteristics of selected endocrine disrupting compounds on activated carbon in natural waters

Water Science & Technology: Water Supply—WSTWS Vol 9 No 1 pp 51–58 © IWA Publishing 2009 doi:10.2166/ws.2009.063

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A. Assoumani, L. Favier-Teodorescu and D. Wolbert

Ecole Nationale Supérieure de Chimie de Rennes,CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, 35700, Rennes Cedex 4, France E-mail: azziz.assoumani@ensc-rennes.fr

Abstract

Bisphenol A (BPA) and ethynylestradiol (EE2), two representative endocrine disrupting compounds (EDCs), were tested for their adsorbabilities onto two powdered activated carbons (PACs). The main aim of the study was to create a prediction tool for the determination of the EDCs adsorbabilities at low ng.L-1 level. Single solute solution adsorption isotherms at high concentrations, for prediction purposes, and low concentrations, for verification of the prediction, were performed for one EDC/PAC couple. Over the whole range of concentration, results showed that the Langmuir-Freundlich model better suits the adsorption phenomenon than the Freundlich or Langmuir model. Kinetics experiments were carried out on the same EDC/PAC couple. HSDM modelling of single solute adsorption kinetics at high concentration allowed determining the kinetic coefficients kf and Ds; both were shown to dominate the mass transfer mechanism. Competitive adsorption isotherms at high and low concentrations showed that downward extrapolation of low concentration adsorption capacities from solely high concentration information results in acceptable error compared to the total range isotherm. The IAST-EBC approach combined with the Langmuir-Freundlich single solute model, for the target compound, and the Langmuir model, for the EBC, appears as an acceptable global model.

Influence of hybrid coagulation-ultrafiltration pretreatment on trace organics adsorption in drinking water treatment

Journal of Water Supply: Research and Technology—AQUA Vol 58 No 3 pp 170–180 © IWA Publishing 2009 doi:10.2166/aqua.2009.071

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S. Müller and W. Uhl

Institute of Urban Water Management (ISI), Chair of Water Supply Engineering, Technische Universität Dresden, Dresden, 01062, Germany Tel.:             +49-(0)351-46333126       Fax: +49-(0)351-46337204 E-mail: wolfgang.uhl@tu-dresden.de

Abstract

The treatment of raw water by hybrid coagulation-ultrafiltration was investigated. Coagulation-ultrafiltration removed high molecular weight organics, preferentially humics. Adsorption of the trace compound cis-1,2-dichloroethene, present in raw water, on granular activated carbon was improved considerably as compounds competing for adsorption space had been removed. This was shown in isotherms and breakthrough curves. Aeration during filtration did not affect membrane performance as expressed in permeability. However, aeration in the submerged membrane container resulted in a release of organic matter from the flocs, which resulted in higher concentrations of dissolved organic carbon in the filtrate.

Phosphorus adsorption on water treatment residual solids

Journal of Water Supply: Research and Technology—AQUA Vol 58 No 1 pp 1–10 © IWA Publishing 2009 doi:10.2166/aqua.2009.017

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Meaghan K. Gibbons, Md. Maruf Mortula and Graham A. Gagnon

Department of Civil and Resource Engineering, Dalhousie University, Halifax, Nova Scotia, B3J 1X1, Canada Tel.:             +1 902 494 3268       Fax:+1 902 494 3108 E-mail: graham.gagnon@dal.ca
Department of Civil Engineering, American University of Sharjah, Sharjah, PO Box, 26666, UAE

Abstract

The treatment and disposal of water treatment plant residual solids has become an increasingly important environmental priority for drinking water utilities. This study examines water treatment residual solids (WTRSs) from four North American water treatment plants to determine the role that coagulant types play in phosphate adsorption by the residual solids. In total, two alum residual solids (one solid from a plant that has a raw water with low alkalinity and one solid from a plant that has a raw water with high alkalinity), one lime residual solid and one ferric residual solid were used in batch adsorption experiments with deionized water at a pH of 6.2±0.2 and secondary municipal wastewater effluent at a pH of 6.8. Langmuir isotherm modeling showed that ferric residuals had the highest adsorptive capacity for phosphate (Qmax=2,960 mg/kg), followed by lime (Qmax=1,390 mg/kg) and alum (Qmax=1,110 mg/kg and 1,030 mg/kg) for adsorption experiments with P-spiked deionized water. Of the two alum residuals, the residual with a higher weight percent of metal oxides had a higher adsorptive capacity. The ferric residuals were less affected by competing species in the wastewater effluent, while the lime and alum residuals had a higher rate of phosphate removal from the deionized water compared to the wastewater effluent. Overall, ferric water treatment residuals were the best adsorbent for phosphate adsorption, followed by lime and alum residuals.

Influence of surface chemistry and structure of activated carbon on adsorption of fulvic acids from water solution

Water Science & Technology—WST Vol 60 No 2 pp 441–447 © IWA Publishing 2009 doi:10.2166/wst.2009.344

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L. A. Savchyna, I. P. Kozyatnyk, T. V. Poliakova and N. A. Klymenko

Institute of Colloid Chemistry and Chemistry of Water, Ukrainian National Academy of Sciences, 42 Vernadsky Avenue, Kiev 03680, Ukraine E-mail: klimenko@carrier.kiev.ua

Abstract

The adsorption of fulvic acids (FA) from aqueous solutions on activated carbon (AC) with different characteristics of surface chemical state has been investigated. To characterize the adsorbability of FA with complex fractional composition, a method of estimation of modified Freundlich equation constants was employed, and “conventional component” was used to evaluate the change in Gibbs free adsorption energy. It has been shown that change in activated carbon surface energy in-homogeneity due to oxidation leads mainly to a decrease in the adsorption energy of fulvic acids and to an increase of the concentration range of the conventional portion of the low adsorbable fraction. Decrease in the adsorption energy of organic substrate may result in higher degree of spontaneous bioregeneration of activated carbon and hence in its longer life in the processes of FA solutions filtration.

Synthesis of carboxylated chitosan and its adsorption properties for cadmium (II), lead (II) and copper (II) from aqueous solutions

Water Science & Technology—WST Vol 60 No 2 pp 467–474 © IWA Publishing 2009 doi:10.2166/wst.2009.369

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K. L. Lv, Y. L. Du and C. M. Wang

Department of Chemistry, Lanzhou University, Lanzhou 730000, China E-mail: wangcm@lzu.edu.cn

Abstract

Carboxylated chitosan (CKCTS) was prepared for the removal of Cd(II), Pb(II), and Cu(II) from aqueous solutions. The effects of experimental parameters such as pH value, initial concentration, contact time and temperature on the adsorption were studied. From the results we can see that the adsorption capacities of Cd(II), Pb(II), and Cu(II) increase with increasing pH of the solution. The kinetic rates were best fitted to the pseudo-second-order model. The adsorption equilibrium data were fitted well with the Langmuir isotherm, which revealed that the maximum adsorption capacities for monolayer saturation of Cd(II), Pb(II), and Cu(II) were 0.555, 0.733 and 0.827 mmol/g, respectively. The adsorption was an exothermic process.

Competitive adsorption of heavy metals in soil underlying an infiltration facility installed in an urban area

Water Science & Technology—WST Vol 59 No 2 pp 303–310 © IWA Publishing 2009 doi:10.2166/wst.2009.865

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M. A. Hossain, H. Furumai and F. Nakajima

Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka, 1000, Bangladesh E-mail: abed@iwfm.buet.ac.bd; abed.hossain@gmail.com
Research Center for Water Environment Technology, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan E-mail: furumai@env.t.u-tokyo.ac.jp
Environmental Science Center, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan E-mail- nakajima@esc.u-tokyo.ac.jp

Abstract

Accumulation of heavy metals at elevated concentration and potential of considerable amount of the accumulated heavy metals to reach the soil system was observed from earlier studies in soakaways sediments within an infiltration facility in Tokyo, Japan. In order to understand the competitive adsorption behaviour of heavy metals Zn, Ni and Cu in soil, competitive batch adsorption experiments were carried out using single metal and binary metal combinations on soil samples representative of underlying soil and surface soil at the site. Speciation analysis of the adsorbed metals was carried out through BCR sequential extraction method. Among the metals, Cu was not affected by competition while Zn and Ni were affected by competition of coexisting metals. The parameters of fitted ‘Freundlich’ and ‘Langmuir’ isotherms indicated more intense competition in underlying soil compared to surface soil for adsorption of Zn and Ni. The speciation of adsorbed metals revealed less selectivity of Zn and Ni to soil organic matter, while dominance of organic bound fraction was observed for Cu, especially in organic rich surface soil. Compared to underlying soil, the surface soil is expected to provide greater adsorption to heavy metals as well as provide greater stability to adsorbed metals, especially for Cu.

 

Categories : Case Studies & Application Stories, Science and Industry Updates

Study of Physico-Chemical Characteristics of Wastewater in an Urban Agglomeration in Romania – MyronLMeters.com

Posted by 11 Feb, 2013

TweetStudy of Physico-Chemical Characteristics of Wastewater in an Urban Agglomeration in Romania Abstract This study investigates the level of wastewater pollution by analyzing its chemical characteristics at five wastewater collectors. Samples are collected before they discharge into the Danube during a monitoring campaign of two weeks. Organic and inorganic compounds, heavy metals, and biogenic compounds […]

Study of Physico-Chemical Characteristics of Wastewater in an Urban Agglomeration in Romania

Abstract

This study investigates the level of wastewater pollution by analyzing its chemical characteristics at five wastewater collectors. Samples are collected before they discharge into the Danube during a monitoring campaign of two weeks. Organic and inorganic compounds, heavy metals, and biogenic compounds have been analyzed using potentiometric and spectrophotometric methods. Experimental results show that the quality of wastewater varies from site to site and it greatly depends on the origin of the wastewater. Correlation analysis was used in order to identify possible relationships between concentrations of various analyzed parameters, which could be used in selecting the appropriate method for wastewater treatment to be implemented at wastewater plants.

1. Introduction

Sources of wastewater in the selected area are microindustries (like laundries, hotels, hospitals, etc.), macroindustries (industrial wastewater) and household activities (domestic wastewater). Wastewater is collected through sewage systems (underground sewage pipes) to one or more centralized Sewage Treatment Plants (STPs), where, ideally, the sewage water is treated. However, in cities and towns with old sewage systems treatment stations sometimes simply do not exist or, if they exist, they might not be properly equipped for an efficient treatment. Even when all establishments are connected to the sewage system, the designed capacities are often exceeded, resulting in a less efficient sewage system and occasional leaks.

Studies of water quality in various effluents revealed that anthropogenic activities have an important negative impact on water quality in the downstream sections of the major rivers. This is a result of cumulative effects from upstream development but also from inadequate wastewater treatment facilities. Water quality decay, characterized by important modifications of chemical oxygen demand (COD), total suspended solids (TSSs), total nitrogen (TN), total phosphorous (TP), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), lead (Pb), and so forth [11] are the result of wastewater discharge in rivers. Water-related environmental quality has been shown to be far from adequate due to unknown characteristics of wastewater . Thus an important element in preventing and controlling river pollution by an effective management of STP is the existence of reliable and accurate information about the concentrations of pollutants in wastewater. Studies of wastewater in Danube basins can be found, for instance, in central and eastern European countries, but we are not aware of extensive studies of wastewater quality at regional/national level in Romania.

This paper analyses the chemical composition of wastewater at several collectors/stations in an important Romanian city, Galati, before being discharged into natural receptors, which in this case are the Danube and Siret Rivers. No sewage treatment existed when the monitoring campaign took place, except the mechanical separation. The study presented here is part of a larger project aiming at establishing the best treatment technology of wastewater at each station. Presently this project is in the implementation stage at all stations. Possible relationships between concentrations of various chemical residues in wastewater and with pollution sources are also investigated. The study is based on daily measurements of chemical parameters at five city collectors in Galati, Romania, during a two-week campaign in February 2010.

2. Experimental Analysis

2.1. Location of Sampling Sites

Galati-Braila area is the second urban agglomeration in Romania after Bucharest, which is located in Romania at the confluence of three major rivers: Danube, Siret, and Prut. The wastewater average flow is about 100000 m3/day . The drainage system covers an area of 2300 ha, serving approximately 99% of the population (approximately 300000 habitants). The basic drainage system is very old, dating back to the end of the 19th century, and was extended along with the expansion of the city due to demographic and industrial evolution. There are several collectors that collect wastewater and rainwater from various areas with very different characteristics, according to the existing water-pipe drainage system. There is no treatment at any station, except for simple mechanical separation. However, industrial wastewater is pretreated before being discharged in the city system. The five wastewater collectors are denoted in the following as S 1 , S 2 , … , S 5. Four of them discharge in the Danube River and the fifth discharges in the Siret River (which is an affluent of Danube River). Figure 1 shows the distribution of the monitoring sites and highlights the type of collecting area (domestic, industrial, or mixed). For the sake of brevity, these stations will be named in the present paper as “domestic,” “mixed,” and “industrial” stations, according to the type of collected wastewater. The mixture between domestic and industrial water at the two mixed collectors is the result of changes in city planning and various transformations of small/medium enterprises.

Figure 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1: Monitoring sampling sites of wastewater from Galati city.

Technical details about each collector/station can be found in Table 1. The first station, S1, collects 10% of the total quantity of wastewater. A high percentage of the water collected at this station comes from domestic sources from the south part of the city (more than 96%). Station S2 collects 64% of the total daily flow of wastewater, out of which 30% comes from domestic sources and the rest (70%) is industrial. Most of the industrial sources in this area are food-production units (milk, braid, wine) while the domestic sources include 20 schools, 4 hospitals, and important social objectives. Station S3 is located in the old part of the city and collects 5% of the total wastewater and has domestic sources. At the fourth station, S4, 11% of the quantity of wastewater is collected from domestic (70%) and industrial (30%) sources. The last collector, S5, collects wastewater from the industrial area of the city, where the most important objectives are a shipyard, metallurgical, and mechanical plants and transport stations.

Table 1

Table 1: Characteristics of collectors S 1 , … , S 5.

2.2. Physico-Chemical Parameters and Methods of Analysis

The physico-chemical parameters which were measured are the following:(i)pH;(ii)chemical oxygen demand (COD) and dissolved oxygen (DO);(iii)nutrients such as nitrate (N-NO3) and phosphate (P-PO4) (these were included due to their impact on the eutrophication phenomenon);(iv)metals such as aluminum (Al+3), soluble iron (Fe+2), and cadmium (Cd+2).

The pH and DO were determined in situ using a portable multiparameter analyzer. Other chemical parameters such as COD, metals and nutrients were determined according to the standard analytical methods for the examination of water and wastewater .

The COD values reflect the organic and inorganic compounds oxidized by dichromate with the following exceptions: some heterocyclic compounds (e.g., pyridine), quaternary nitrogen compounds, and readily volatile hydrocarbons. The concentration of metals (Al+3, Cd+2, Fe+2) was determined as a result of their toxicity.

The value of pH was analyzed according to the Romanian Standard using a portable multiparameter analyzer, Consort C932.

COD parameter was measured using COD Vials (COD 25–1500 mg/L, Merck, Germany). The digestion process of 3 mL aliquots was carried out in the COD Vials for 2 h at 148°C. The absorbance level of the digested samples was then measured with a spectrophotometer at λ = 605 nm (Spectroquant NOVA 60, Merck, Germany), the method being analogous to EPA methods [20], US Standard Methods, and Romanian Standard Methods.

The DO parameter was analyzed according to Romanian Standard using a portable multiparameter analyzer, Consort C932.

Aluminum ions (Al+3) were determined using Al Vials (Aluminum Test 0.020–1.20 mg/L, Merck, Germany) in a way analogous to US Standard Methods. The absorbance levels of the samples were then measured with a spectrophotometer (Spectroquant NOVA 60; Merck, Germany) at λ = 550 nm. The method was based on reaction between aluminum ions and Chromazurol S, in weakly acidic-acetate buffered solution, to form a blue-violet compound that is determined spectrophotometrically. The pH of the sample must be within range 3–10. Where necessary, the pH will be adjusted with sodium hydroxide solution or sulphuric acid.

Iron concentration (Fe+2) was determined using Iron Vials (Iron Test 0.005–5.00 mg/L, Merck, Germany) and their absorbance levels were then measured using a spectrophotometer (Spectroquant NOVA 60; Merck, Germany) at λ = 565 nm. The method was based on reducing all iron ions (Fe+3) to iron ions (Fe+2). In a thioglycolate-buffered medium, these react with a triazine derivative to form a red-violet complex which is spectrophotometrically determined. The pH must be within range 3–11. Where necessary the pH was adjusted with sodium hydroxide solution or sulphuric acid.

Cadmium ions (Cd+2) were determined using Cadmium Vials (Cadmium Test 0.005–5.00 mg/L, Merck, Germany), their absorbance levels being measured with a spectrophotometer (Spectroquant NOVA 60; Merck, Germany) at λ = 525 nm. The method was based on the reaction of cadmium ions with a cadion derivative (cadion-trivial name for 1-(4-nitrophenyl)-3-(4-phenylazophenyl)triazene), in alkaline solution, to form a red complex that is determined spectrophotometrically. The pH must be within the range 3–11, and, if not, the pH will be adjusted with sodium hydroxide solution or sulphuric acid.

Nitrogen content was determined using Nitrate Vials (Nitrate Cell test in seawater 0.10–3.00 mg/L NO3-N or 0.4–13.3 mg/L N O3 −, Merck, Germany). The method being based on the reaction of nitrate ions with resorcinol, in the presence of chloride, in a strongly sulphuric acid solution, to form a red-violet indophenols dye that is determined spectrophotometrically. The absorbance levels of the samples were then measured with a spectrophotometer (Spectroquant NOVA 60; Merck, Germany) at λ = 500 nm.

Phosphorous content was determined using Phosphate Vials (Phosphate Cell Test 0.5–25.0 mg/L PO4-P or 1.5–76.7 mg/L P O4 − 3, Merck, Germany) with a method that was analogous to the US Standard Methods [17]. The method was based on the reaction of orthophosphate anions, in a sulphuric solution, with ammonium vanadate and ammonium heptamolybdate to form orange-yellow molybdo-vanado-phosphoric acid that is determined spectrophotometrically (“VM” method). The absorbance levels of the samples were then measured with a spectrophotometer (Spectroquant NOVA 60; Merck, Germany) at λ = 410 nm.

All results were compared with standardized levels for wastewater quality found in accordance with European Commission Directive [23] and Romanian law [24].

3. Results and Discussion

3.1. The Acidity (pH)

The results for pH for all the investigated five collectors are shown in Figure 2.

Figure 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2: Daily variation of pH at all sites.

Generally, the wastewater collected at the monitored sites is slightly alkaline. The pH varies between 6.8 and 8.3—average value 7.82—thus the pH values are within the accepted range for Danube River according to the Romanian law, which is between 6.5 and 9.0. The pH variation is relatively similar at collectors S1–S4 (domestic and/or mixed domestic-industrial contribution). Lower pH values are observed at S5, which is dominated by industrial wastewater, originating from major enterprises and heavy industry. However, these values are not too low, since usually pH values for industrial wastewater are smaller than 6.5.

A significant decrease in the pH value was observed during the 8th day of the analyzed period at each station. Interestingly, a heavy snowfall took place at that particular time, thus the decrease could be attributed to the mixing between wastewater and a high quantity of low pH water, resulted from the melting of snow . One could speculate that the snowfall, which has an acidic character, might have affected the pH of the wastewater through “run off” phenomena.

No other snowfall took place during the monitoring campaign, thus no definite conclusion can be drawn for a possible relationship between pH and snowfalls.

3.2. Results for Chemical Oxygen Demand (COD)

Detection of COD values in each sampling site of wastewater is presented in Figure 3.

Figure 3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3: Daily variation of COD at all sites.

All COD values are higher than the maximum accepted values (125 mg O2/L) of the Romanian Law . Both organic and inorganic compounds have an effect on urban wastewater’s oxidability since COD represents not only oxidation of organic compounds, but also the oxidation of reductive inorganic compounds. That means some inorganic compounds interfere with COD determination through the consumption of C r2O7 − 2. Two different behaviors can be observed, which are associated with the type of the collected wastewater as follows.(i)The first group consists of stations S2, S4 and S5 where the wastewater has an important industrial component. At these stations, COD values are approximately between 150 and 300 mg O2/L, smaller, for instance, than COD values found by in the raw wastewater produced by an industrial coffee plant where COD values were between 4000 and 4600 mg O2/L. Also, the temporal variation of COD values at all three stations is similar with no significant deviations from the average value, which is about 250 mg O2/L. Interestingly, the lowest COD level can be seen, on the average, at S5, which has the highest percentage of industrial wastewater. The second group comprises the “domestic” stations S1 and S3. The COD levels are higher, with values of 500 mg O2/L or more. Also, the variability is clearly higher than at the industrial-type stations. No clear association between the variations at the two sites can be seen. A peak in COD was measured in the 14th day of the study at site S1 (1160 mg O2/L). Since S1 is a domestic type station, it is unlikely that some major discharge led to such a high variation of COD. Unfortunately, no other information exists that might indicate a possible cause for this increase.

3.3. Results for Dissolved Oxygen (DO)

The amount of DO, which represents the concentration of chemical or biological compounds that can be oxidized and that might have pollution potential, can affect a sum of processes that include re-aeration, transport, photosynthesis, respiration, nitrification, and decay of organic matter. Low DO concentrations can lead to impaired fish development and maturation, increased fish mortality, and underwater habitat degradation . No standards are given by Romanian or European Law for DO in wastewater. The DO values for the analyzed wastewater at all five sites are shown in Figure 4.

Figure 4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4: Daily variation of DO at all sites.

Concentration of DO varies at all sampling sites and has values between 0.96 (at S2) and 11.33 (at S4) mg O2/L with a mean value of 6.39 mg O2/L. These are clearly higher than DO values measured, for instance, in surface natural waters in China, where the Taihu watershed had the lowest DO level (2.70 mg/L), while in other rivers DO varied from 3.14 to 3.36 mg O2/L [34]. On the other hand, such high values of DO (9.0 mg O2/L) could be found, for instance, in the Santa Cruz River , who argued that discharging industry and domestic wastewater induced serious organic pollution in rivers, since the decrease of DO was mainly caused by the decomposition of organic compounds. Extremely low DO content (DO < 2 mg O2/L) usually indicates the degradation of an aquatic system .

The DO levels vary similarly for all selected sampling sites. The DO levels cover a wide range, with a minimum value of 1.0 mg O2/L at S1 and S3 and a maximum value of 11.33 mg O2/L at S4. There is a drop in DO at all stations, observed is in the 8th day of the monitoring interval, which coincides with the day when a similar decrease in pH took place. The lowest values of DO are observed for S1, one of the two “domestic” stations. It is interesting to note that DO at S5 is low although the wastewater here comes only from industry sources.

3.4. Metals

The variation of Al+3, Fe+2, and Cd+2 concentrations in wastewater are shown in Figures 5, 6, and 7. Al+3 concentrations (Figure 5) were mostly within the 0.05–0.20 mg/L range at all the sampling sites. However, during the beginning and the end of the monitoring campaign, Al+3 concentration at station S2 is high (reaching even 0.65 mg/L), nonetheless below the limit imposed by the Romanian law, which is 5 mg/L . The fact that in the beginning of the time interval, the concentration of Al+3 is high at two neighboring stations (S1 and S2) suggests that some localized discharge affecting both runaway and waste water, might have happened in the southern part of the city, which led to the increase of Al+3concentration in the collected wastewater. This is supported by the fact that the concentration gradually decreases at S2.

 

Figure 5: Daily variation of Al at all sites.

Figure 5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 6: Daily variation of Fe at all sites.

Figure 6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 7: Daily variation of Cd at all sites.

Figure 7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The variation of Fe+2 concentrations is shown in Figure 6. Fe+2 concentration is within the 0.07–0.4 mg/L interval, below 5.0 mg/L, which is the maximum accepted value of the Romanian law . Two higher values were observed at S2 and S4 (both with industrial component) during the third and fourth days of the monitoring campaign.

Besides Al+3 and Fe+2, concentrations of Cd+2 were determined and the variations at the five stations are shown in Figure 7. Cd+2 is a rare pollutant, originating from heavy industry. Leakages in the sewage systems can also lead to Cd+2. Except for two days, Cd+2 varies between 0.005 and 0.04 mg/L. The two high values of 0.11 mg/L were observed in the first and fourth days at S5, which collects industrial wastewater. However, Cd+2 concentrations do not exceed the maximum accepted values of the Romanian law [24] for the monitoring interval which is 0.2 mg/L.

3.5. Nutrients

Water systems are very vulnerable to nitrate pollution sources like septic systems, animal waste, commercial fertilizers, and decaying organic matter [37]. Important quantities of nutrients, which are impossible to be removed naturally, can be found in rivers and this leads to the eutrophication of natural water (like Danube River). As a result, an increase in the lifetime of pathogenic microorganisms is expected. Measurement of nutrient (different forms of nitrogen (N) or phosphorous (P)) variations in domestic wastewater is strongly needed in order to maintain the water quality of receptors [36]. Nitrogen by nitrate (Figure 8) and phosphorous by phosphate (Figure 9) are considered as representative for nutrients.

Figure 8: Daily variation of N-NO3 at all sites.

Figure 8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 9: Daily variation of P-PO4 at all sites.

Figure 9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 8 shows that N-NO3 concentrations vary, on the average, between 0 and 5.0 mg/L.

At all four stations with a domestic component, S1, S2, S3 and S4, the concentration of N-NO3 is low (between 0 and 1.5 mg/L) and the daily variation is relatively similar at all sites. Noticeable drops of the N-NO3 concentration are observed at all stations in the 8th day of the monitoring interval, coinciding with pH (Figure 2) and DO strong variations (Figure 4). This supports the conclusion that the heavy snowfall recorded at that period had an important impact on wastewater quality most likely due to the runoff joining the sewage system.

The behavior of N-NO3 clearly differs at station S5, which collects only industrial wastewater. Significantly higher values of N-NO3, ranging from 2.0 to 5.0 mg/L, were detected. However, the mean concentration of N-NO3 remained below the maximum concentration given by the Romanian law [24]. Obviously, if treatment stations have to be set up, the priority for this particular nutrient component should concentrate on stations where industrial wastewater is collected.

Another nutrient that was analyzed for our study was orthophosphate expressed by phosphorous. The P-PO4 concentration varies, on the average, between 1.0 and 6.0 mg/L (Figure 9). For this component, concentrations are higher at domestic stations, S1 and S3, than at the other three stations. P-PO4 is expected to increase in domestic wastewater because of food, more precisely meat, processing, washing, and so forth. The lowest values were observed at S5, which has a negligible domestic component. Peaks in the P-PO4 concentration are observed at S1. Interestingly enough, P-PO4 temporal variations correlated pretty well at stations S2, S4, and S5 (which collect industrial wastewater). Unlike most of the other analyzed compounds, for which the concentrations were within the accepted ranges, the maximum level of P-PO4 is exceeded at all five collectors. Both Romanian law  and the European law  stipulate 2.0 mg/L total phosphorous for 10000–100000 habitants, and for more than 100000 habitants (as in Galati City’s case) 1.0 mg/L total phosphorus. Interestingly, domestic stations seem to require more attention with respect to the quality of water then industrial stations.

Our results regarding the variation and levels of the analyzed parameters are grouped below as the following.(1)The values of pH are within the accepted range for Danube, and their daily variations are relatively similar for both domestic and mixed wastewater. Significantly smaller pH values were measured in the wastewater with a high industrial load. A clear minimum was observed at all sites in the 8th day of the monitoring period, when a heavy snowfall took place. One could speculate that the snowfall, which has an acidic character, might have affected the pH of the wastewater through “run off” phenomena. However, a clear connection cannot be established relying on one event only.(2)The COD level clearly depends on the type of wastewater. Higher values were observed for domestic wastewater, while “pure” industrial wastewater has the lowest COD. This might be explained by the fact that industrial wastewater benefits from some treatment before being discharged into the city sewage system. However, COD does exceed the maximum accepted values according to the Romanian law [24] at all sites thus additional treatment is required at all stations.(3)Concentrations of all analysed metals, Al+3, Cd+2 and Fe+2, are within the limit of the Romanian law. No association with the type of wastewater could be inferred. Isolated peaks could not be linked with any specific polluting factors, except for Cd+2, for which accidental concentration increases are observed for pure industrial wastewater.(4)The level of P-PO4, one of the two nutrients that were analyzed, was high at all stations; however, the highest concentrations are associated with domestic loads.(5)Opposingly, the N-NO3 level is the highest, by far, in wastewater with a high industrial contribution.

3.6. Possible Relationships between Various Parameters

The experimental results have shown that some parameters might be related and that their behavior greatly depends on the type of collected wastewater. Differences between the behavior of physico-chemical parameters at the domestic sites (S1 and S3), on one hand, and at the other sites, on the other, was observed. Pearson correlation coefficients have been calculated between all parameters at all the selected five sites and corresponding significances. Although most of correlations were not significant, some interesting connections between various parameters at sites with similar characteristics were revealed. Table 2 shows correlation coefficients between various parameters for all five stations. Significant correlations at different types of stations are denoted as follows: italicized fonts for domestic stations, boldface italicized fonts for the industrial station and boldface fonts for mixed stations.

Table 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 2: Correlation coefficients calculated for station S1 to S5. Significant correlations at each type of stations are identified as follows: boldface italicized fonts for industrial station (S5), italicized fonts for domestic stations (S1 and S3) and boldface fonts for mixed stations (S2 and S4).

An important relationship seems to exist between pH and N-NO3 at all stations except for the industrial wastewater collecting site, S5 (i.e., at all stations collecting wastewater resulting from domestic activities). Similarly, pH correlates well with DO at all stations except the industrial one.

COD correlates with two metals, Cd+2 and soluble Fe+2, which is expected [30], but only at S1 and S3, where the daily variations of the concentration for these two metals (Cd+2 and soluble Fe+2) were similar.

No conclusion can be drawn for the industrial wastewater collector that was analyzed, where both positive and negative correlations were observed. The lack of correlation between the two metals and COD at the industrial wastewater collectors suggests that other processes, that alter the chemical equilibrium between the two chemical compounds, must be taken into account. For example some metals are complexed by organic compounds that are present in the water and the pH values can influence these phenomena.

DO correlates with pH and N-NO3 at all four sampling stations with domestic component (S1–S4) but the relationship vanish at S5 (industrial). There is also a negative correlation between DO and Fe+2 and Cd+2 only for domestic wastewater, which is expected because of the natural oxidation of metals. The correlation vanishes at the other three stations which collect wastewater from industrial areas.

Heavy metals, Fe+2 and Cd+2 correlate only at domestic stations and no relationships can be defined to link the concentration of Al+3 with other components.

The P-PO4 variation is linked to the variation of soluble Fe+2 at the two stations that collect domestic wastewater. Interestingly, these two elements exist together in reductive domestic systems because these are dominated by proteins, lipids, degradation products. This relationship disappears at the other stations, where the industrial load is significant. The other metals, Al+3, seems to be linked with P-PO4at stations S5 and S2, which collect wastewater with the highest industrial load. No link is observed for the rest of stations and for Cd+2 which can be explained by a higher probability of iron (II) orthophosphate to form in wastewater compared to Al+3 or Cd+2 orthophosphates.

Positive correlations can also be seen between P-PO4 and COD for all sampling sites except S1, where the relationship is still positive but less significant. The other nutrient, N-NO3, is anticorrelated with COD but only at S3 and is well correlated with pH and DO at all four stations with domestic component. The only exception is station S5, which collects mostly industrial wastewater.

Concluding, positive correlations were observed between the following parameters.(1)pH and N-NO3 everywhere except “purely” industrial water.(2)COD and soluble Fe+2 at domestic stations.(3)DO and pH, on the one hand, and DO and N-NO3 at domestic stations.(4)P-PO4 and soluble Fe+2 at domestic stations.(5)P-PO4 and COD everywhere, which, taking into account the high level of P-PO4 at domestic stations, might suggest that one important contributor to water quality degradation are household discharges.(6)Al+3 and P-PO4.

4. Conclusions

In the present paper we have analyzed the daily variation of several physico-chemical parameters of the wastewater (pH, COD, DO, Al+3, Fe+2, Cd+2, N-NO3, and P-PO4) at five collectors that have been characterized as domestic, industrial and mixed, according to the type of collecting area. Different results have been obtained for domestic and industrial wastewater. Most of the chemical parameters are within accepted ranges. Nevertheless, their values as well as their behavior depend significantly on the type of collected wastewater.

The overall conclusion is that wastewater with a high domestic load has the highest negative impact on water quality in a river. On the other hand, industrial wastewater brings an important nutrient load, with potentially negative effect on the basins where it is discharged. Our results suggested that meteorological factors (snow) might modify some characteristics of wastewater, but a clear connection cannot be established relying on one event only.

Significantly smaller pH values were measured in the wastewater with a high industrial load. The COD level clearly depends on the type of wastewater. Higher values were observed for wastewater with domestic sources, while “pure” industrial wastewater has the lowest COD. This might be explained by the fact that industrial wastewater benefits from some treatment before being discharged into the city sewage system. COD does exceed the maximum accepted values according to the Romanian law at all sites thus additional treatment is required at all stations. Accidental increases of Cd+2 concentrations are observed for pure industrial wastewater. The highest concentrations of P-PO4 are associated with domestic loads. Opposing, the N-NO3 level is clearly the highest in wastewater with a high industrial contribution.

Correlation analysis has been used in order to identify possible relationships between various parameters for wastewater of similar origin.

Positive correlations between various physico-chemical parameters exist for the domestic wastewater (DO, pH and N-NO3, on the one hand, and P-PO4, COD and soluble Fe+2, on the other hand). Except for two cases, these relationships break when the industrial load is high. Some of the existing correlations are expected as discussed above, thus any removal treatment should be differentiated according to the type of collector, before discharging it into the natural receptors in order to be costly efficient. Correlations between DO and COD and nutrient load suggest that the most important threat for natural basins in the studied area, are domestic sources for the wastewater.

The different percentages of industrial and domestic collected wastewater vary at each station, which has a clear impact on concentrations of the selected chemical components. Our results show that domestic wastewater has a higher negative impact on water quality than wastewater with a high industrial load, which, surprisingly, seems to be cleaner. This might be related to the fact that most industries are forced, by law, to apply a pretreatment before discharging wastewater into the city sewage system. Industrial wastewater affects the nutrient content of natural water basins. Although the time period was relatively short, our study identified specific requirements of chemical treatment at each station. An efficient treatment plan should take into account the type of wastewater to be processed at each station. Results presented here are linked with another research topic assessing the level of water quality in the lower basin of the Danube before and after implementing the complete biochemical treatment plants.

Acknowledgment

The work of Catalin Trif was supported by Project SOP HRD-EFICIENT 61445/2009.

Copyright © 2012 Paula Popa et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited – original found here: http://www.hindawi.com/journals/tswj/2012/549028/

 

 

Categories : Case Studies & Application Stories, Science and Industry Updates

Ultraviolet Water Purification – MyronLMeters.com

Posted by 30 Jan, 2013

Tweet A low pressure mercury vapor discharge tube floods the inside of a biosafety cabinet with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces. Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses ultraviolet (UV) light at sufficiently short wavelength to kill microorganisms. It is used in a variety […]

A low pressure mercury vapor discharge tube floods the inside of a biosafety cabinet with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces.

A low pressure mercury vapor discharge tube floods the inside of a biosafety cabinet with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces.

Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses ultraviolet (UV) light at sufficiently short wavelength to kill microorganisms. It is used in a variety of applications, such as food, air and water purification. UVGI uses short-wavelength ultraviolet radiation that is harmful to microorganisms. It is effective in destroying the nucleic acids in these organisms so that their DNA is disrupted by the UV radiation, leaving them unable to perform vital cellular functions.

The wavelength of UV that causes this effect is rare on Earth as the atmosphere blocks it. Using a UVGI device in certain environments like circulating air or water systems creates a deadly effect on micro-organisms such as pathogens, viruses and molds that are in these environments. Coupled with a filtration system, UVGI can remove harmful microorganisms from these environments.

The application of UVGI to disinfection has been an accepted practice since the mid-20th century. It has been used primarily in medical sanitation and sterile work facilities. Increasingly it was employed to sterilize drinking and wastewater, as the holding facilities were enclosed and could be circulated to ensure a higher exposure to the UV. In recent years UVGI has found renewed application in air sanitizing.

UV has been a known mutagen at the cellular level for more than one-hundred years. The 1903 Nobel Prize for Medicine was awarded to Niels Finsen for his use of UV against lupus vulgaris, tuberculosis of the skin.

Using ultraviolet (UV) light for drinking water disinfection dates back to 1916 in the U.S. Over the years, UV costs have declined as researchers develop and use new UV methods to disinfect water and wastewater. Currently, several states have developed regulations that allow systems to disinfect their drinking water supplies with UV light.

Method

Ultraviolet light is electromagnetic radiation with wavelengths shorter than visible light. UV can be separated into various ranges, with short range UV (UVC) considered “germicidal UV.” At certain wavelengths UV is mutagenic to bacteria, viruses and other microorganisms. At a wavelength of 2,537 Angstroms (254 nm) UV will break the molecular bonds within micro-organismal DNA, producing thymine dimers in their DNA thereby destroying them, rendering them harmless or prohibiting growth and reproduction. It is a process similar to the UV effect of longer wavelengths (UVB) on humans, such as sunburn or sun glare. Microorganisms have less protection from UV and cannot survive prolonged exposure to it.

A UVGI system is designed to expose environments such as water tanks, sealed rooms and forced air systems to germicidal UV. Exposure comes from germicidal lamps that emit germicidal UV electromagnetic radiation at the correct wavelength, thus irradiating the environment. The forced flow of air or water through this environment ensures the exposure.

Effectiveness

The effectiveness of germicidal UV in such an environment depends on a number of factors: the length of time a micro-organism is exposed to UV, power fluctuations of the UV source that impact the EM wavelength, the presence of particles that can protect the micro-organisms from UV, and a micro-organism’s ability to withstand UV during its exposure.

In many systems redundancy in exposing micro-organisms to UV is achieved by circulating the air or water repeatedly. This ensures multiple passes so that the UV is effective against the highest number of micro-organisms and will irradiate resistant micro-organisms more than once to break them down.

The effectiveness of this form of sterilization is also dependent on line-of-sight exposure of the micro-organisms to the UV light. Environments where design creates obstacles that block the UV light are not as effective. In such an environment the effectiveness is then reliant on the placement of the UVGI system so that line-of-sight is optimum for sterilization.

Sterilization is often misquoted as being achievable. While it is theoretically possible in a controlled environment, it is very difficult to prove and the term ‘disinfection’ is used by companies offering this service as to avoid legal reprimand. Specialist companies will often advertise a certain log reduction i.e. 99.9999% effective, instead of sterilization. This takes into consideration a phenomenon known as light and dark repair (photoreactivation and excision (BER) respectively) in which the DNA in the bacterium will fix itself after being damaged by UV light.

A separate problem that will affect UVGI is dust or other film coating the bulb, which can lower UV output. Therefore bulbs require annual replacement and scheduled cleaning to ensure effectiveness. The lifetime of germicidal UV bulbs varies depending on design. Also the material that the bulb is made of can absorb some of the germicidal rays.

Lamp cooling under airflow can also lower UV output, thus care should be taken to shield lamps from direct airflow via parabolic reflector. Or add additional lamps to compensate for the cooling effect.
Increases in effectiveness and UV intensity can be achieved by using reflection. Aluminium has the highest reflectivity rate versus other metals and is recommended when using UV.

Inactivation of microorganisms

The degree of inactivation by ultraviolet radiation is directly related to the UV dose applied to the water. The dosage, a product of UV light intensity and exposure time, is usually measured in microjoules per square centimeter, or alternatively as microwatt seconds per square centimeter (µW·s/cm2). Dosages for a 90% kill of most bacteria and virus range from 2,000 to 8,000 µW·s/cm2. Dosage for larger parasites such as Cryptosporidium require a lower dose for inactivation. As a result, the US EPA has accepted UV disinfection as a method for drinking water plants to obtain Cryptosporidium, Giardia or virus inactivation credits. For example, for one-decimal-logarithm reduction of Cryptosporidium, a minimum dose of 2,500 µW·s/cm2 is required based on the US EPA UV Guidance Manual published in 2006.

Weaknesses and strengths

Advantages

UV water treatment devices can be used for well water and surface water disinfection. UV treatment compares favorably with other water disinfection systems in terms of cost, labor and the need for technically trained personnel for operation: deep tube wells fitted with hand pumps, while perhaps the simplest to operate, require expensive drilling rigs, are immobile sources, and often produce hard water that is found distasteful. Chlorine disinfection treats larger organisms and offers residual disinfection, but these systems are expensive because they need a special operator training and a steady supply of a potentially hazardous material. Finally, boiling water over a biomass cook stove is the most reliable treatment method but it demands labor, and imposes a high economic cost. UV treatment is rapid and, in terms of primary energy use, approximately 20,000 times more efficient than boiling.

Drawbacks

UV disinfection is most effective for treating a high clarity purified reverse osmosis distilled water. Suspended particles are a problem because microorganisms buried within particles are shielded from the UV light and pass through the unit unaffected. However, UV systems can be coupled with a pre-filter to remove those larger organisms that would otherwise pass through the UV system unaffected. The pre-filter also clarifies the water to improve light transmittance and therefore UV dose throughout the entire water column. Another key factor of UV water treatment is the flow rate: if the flow is too high, water will pass through without enough UV exposure. If the flow is too low, heat may build up and damage the UV lamp.

Safety

In UVGI systems the lamps are shielded or are in environments that limit exposure, such as a closed water tank or closed air circulation system, often with interlocks that automatically shut off the UV lamps if the system is opened for access by human beings.

In human beings, skin exposure to germicidal wavelengths of UV light can produce sunburn and skin cancer. Exposure of the eyes to this UV radiation can produce extremely painful inflammation of the cornea and temporary or permanent vision impairment, up to and including blindness in some cases. UV can damage the retina of the eye.

Another potential danger is the UV production of ozone. Ozone can be harmful to health. The United States Environmental Protection Agency designated 0.05 parts per million (ppm) of ozone to be a safe level. Lamps designed to release UVC and higher frequencies are doped so that any UV light below 254 nm will not be released, thus ozone is not produced. A full spectrum lamp will release all UV wavelengths and will produce ozone as well as UVC, UVB, and UVA. (The ozone is produced when UVC hits oxygen (O2) molecules, and so is only produced when oxygen is present.)

UV-C radiation is able to break down chemical bonds. This leads to rapid ageing of plastics (insulations, gasket) and other materials. Note that plastics sold to be “UV-resistant” are tested only for UV-B, as UV-C doesn’t normally reach the surface of the Earth. When UV is used near plastic, rubber, or insulations care should be taken to shield said components; metal tape or aluminum foil will suffice.

A disadvantage of the technique is that water treated by chlorination is resistant to reinfection, where UVGI water must be transported and delivered in such a way as to avoid contamination.

Uses

Air disinfection

UVGI can be used to disinfect air with prolonged exposure. Disinfection is a function of UV concentration and time, CT. For this reason, it is not as effective on moving air, when the lamp is perpendicular to the flow, as exposure times are dramatically reduced. Air purification UVGI systems can be freestanding units with shielded UV lamps that use a fan to force air past the UV light. Other systems are installed in forced air systems so that the circulation for the premises moves micro-organisms past the lamps. Key to this form of sterilization is placement of the UV lamps and a good filtration system to remove the dead micro-organisms.[8] For example, forced air systems by design impede line-of-sight, thus creating areas of the environment that will be shaded from the UV light. However, a UV lamp placed at the coils and drainpan of cooling system will keep micro-organisms from forming in these naturally damp places.

ASHRAE covers UVGI and its applications in IAQ and building maintenance in its 2008 Handbook, HVAC Systems and Equipment in Chapter 16 titled Ultraviolet Lamp Systems. ASHRAE’s 2011 Handbook, HVAC Applications, covers ULTRAVIOLET AIR AND SURFACE TREATMENT in Chapter 60.

Water sterilization

Ultraviolet disinfection of water consists of a purely physical, chemical-free process. UV-C radiation attacks the vital DNA of the bacteria directly. The bacteria lose their reproductive capability and are destroyed. Even parasites such as Cryptosporidia or Giardia, which are extremely resistant to chemical disinfectants, are efficiently reduced.[9] UV can also be used to remove chlorine and chloramine species from water ; this process is called photolysis, and requires a higher dose than normal disinfection. The sterilized microorganisms are not removed from the water. UV disinfection does not remove dissolved organics, inorganic compounds or particles in the water.[10] However, UV-oxidation processes can be used to simultaneously destroy trace chemical contaminants and provide high-level disinfection, such as the world’s largest indirect potable reuse plant in Orange County, California.[11] That title will soon be taken by New York which is set to open the Catskill-Delaware Water Ultraviolet Disinfection Facility, by the end of 2012. A total of 56 energy-efficient UV reactors will be installed to treat 2.2 billion US gallons (8,300,000 m3) a day to serve New York City.

UV disinfection leaves no taint, chemicals or residues in the treated water. Disinfection using UV light is quick and clean.

UV tube project

The UV Tube is a design concept for providing inexpensive water disinfection to people in poor countries. The concept is based the ability of ultraviolet light to kill infectious agents by disrupting their DNA. It was initially developed under an “open source” model at the Renewable and Appropriate Energy Laboratory at the University of California, Berkeley. The form and composition of the UV Tube can vary depending on the resources available and the preferences of those building and using the device. However, certain geometric parameters must be maintained to ensure consistent performance. Several different versions of the UV Tube are currently being used in multiple locations in Mexico and Sri Lanka.

Technology

Germicidal lamp

Germicidal UV is delivered by a mercury-vapor lamp that emits UV at the germicidal wavelength. Mercury vapour emits at 254 nm. Many germicidal UV bulbs use special ballasts to regulate electrical current flow to the bulbs, similar to those needed for fluorescent lights. In some cases, UVGI electrodeless lamps can be energised with microwaves, giving very long stable life and other advantages[clarification needed]. This is known as ‘Microwave UV.’

Lamps are either amalgam or medium pressure lamps. Each type has specific strengths and weaknesses.
Low-pressure UV lamps
These offer high efficiencies (approx 35% UVC) but lower power, typically 1 W/cm power density (power per unit of arc length).

Amalgam UV lamps
A high-power version of low-pressure lamps. They operate at higher temperatures and have a lifetime of up to 16,000 hours. Their efficiency is slightly lower than that of traditional low-pressure lamps (approx 33% UVC output) and power density is approx 2–3 W/cm.

Medium-pressure UV
These lamps have a broad and pronounced peak-line spectrum and a high radiation output but lower UVC efficiency of 10% or less. Typical power density is 30 W/cm³ or greater.
Depending on the quartz glass used for the lamp body, low-pressure and amalgam UV lamps emit light at 254 nm and 185 nm (for oxidation). 185 nm light is used to generate ozone.

The UV units for water treatment consist of a specialized low pressure mercury vapor lamp that produces ultraviolet radiation at 254 nm, or medium pressure UV lamps that produce a polychromatic output from 200 nm to visible and infrared energy. The optimal wavelengths for disinfection are close to 260 nm. Medium pressure lamps are approximately 12% efficient, whilst amalgam low pressure lamps can be up to 40% efficient. The UV lamp never contacts the water, it is either housed in a quartz glass sleeve inside the water chamber or mounted external to the water which flows through the transparent UV tube. It is mounted so that water can pass through a flow chamber, and UV rays are admitted and absorbed into the stream.

Sizing of a UV system is affected by three variables: flow rate, lamp power and UV transmittance in the water. UV manufacturers typically developed sophisticated Computational Fluid Dynamics (CFD) models validated with bioassay testing. This typically involves testing the UV reactor’s disinfection performance with either MS2 or T1 bacteriophages at various flow rates, UV transmittance and power levels in order to develop a regression model for system sizing. For example, this is a requirement for all drinking water systems in the United States per the US EPA UV Guidance Manual.[6]:5-2

The flow profile is produced from the chamber geometry, flow rate and particular turbulence model selected. The radiation profile is developed from inputs such as water quality, lamp type (power, germicidal efficiency, spectral output, arc length) and the transmittance and dimension of the quartz sleeve. Proprietary CFD software simulates both the flow and radiation profiles. Once the 3-D model of the chamber is built, it’s populated with a grid or mesh that comprises thousands of small cubes.

Points of interest—such as at a bend, on the quartz sleeve surface, or around the wiper mechanism—use a higher resolution mesh, whilst other areas within the reactor use a coarse mesh. Once the mesh is produced, hundreds of thousands of virtual particles are “fired” through the chamber. Each particle has several variables of interest associated with it, and the particles are “harvested” after the reactor. Discrete phase modeling produces delivered dose, headless and other chamber specific parameters.

When the modeling phase is complete, selected systems are validated using a professional third party to provide oversight and to determine how closely the model is able to predict the reality of system performance. System validation uses non-pathogenic surrogates to determine the Reduction Equivalent Dose (RED) ability of the reactors. Most systems are validated to deliver 40 mJ/[cm.sup.2] within an envelope of flow and transmittance.
To validate effectiveness in drinking water systems, the methods described in the US EPA UV Guidance Manual is typically used by the U.S. Environmental Protection Agency, whilst Europe has adopted Germany’s DVGW 294 standard. For wastewater systems, the NWRI/AwwaRF Ultraviolet Disinfection Guidelines for Drinking Water and Water Reuse protocols are typically used, especially in wastewater reuse applications.[14]
UV systems destined for drinking water applications are validated using a third party test house to demonstrate system capability, and usually a non pathogenic surrogate such as MS 2 phage or Bacillus Subtilis is used to verify actual system performance. UV manufacturers have verified the performance of a number of reactors, in each case iteratively improving the predictive models.

Wastewater treatment

Ultraviolet in wastewater treatment is replacing chlorination due to the chemical’s toxic by-products. Individual wastestreams to be treated by UVGI must be tested to ensure that the method will be effective due to potential interferences such as suspended solids, dyes or other substances that may block or absorb the UV radiation.

“UV units to treat small batches (1 to several liters) or low flows (1 to several liters per minute) of water at the community level are estimated to have costs of 0.02 US$ per 1000 liters of water, including the cost of electricity and consumables and the annualized capital cost of the unit.” (WHO)

Large scale urban UV wastewater treatment is performed in cities such as Edmonton, Alberta. The use of ultraviolet light has now become standard practice in most municipal wastewater treatment processes. Effluent is now starting to be recognised as a valuable resource, not a problem that needs to be dumped. Many wastewater facilities are being renamed as water reclamation facilities, and whether the waste water is being discharged into a river, being used to irrigate crops, or injected into an aquifer for later recovery. Ultraviolet light is now being used to ensure water is free from harmful organisms.

Aquarium and pond

Ultraviolet sterilizers are often used in aquaria and ponds to help control unwanted microorganisms in the water. Continuous sterilization of the water neutralizes single-cell algae and thereby increases water clarity. UV irradiation also ensures that exposed pathogens cannot reproduce, thus decreasing the likelihood of a disease outbreak in an aquarium. UV irradiation can also have a positive impact on an Aquariums Redox balance
Aquarium and pond sterilizers are typically small, with fittings for tubing that allows the water to flow through the sterilizer on its way from a separate external filter or water pump. Within the sterilizer, water flows as close as possible to the ultraviolet light source. Water pre-filtration is critical so as to lower water turbidity which will lower UVC penetration. Many of the better UV Sterilizers have long dwell times and limit the space between the UVC source and the inside wall of the UV Sterilizer device.

Laboratory hygiene

UVGI is often used to disinfect equipment such as safety goggles, instruments, pipettes, and other devices. Lab personnel also disinfects glassware and plasticware this way. Microbiology laboratories use UVGI to disinfect surfaces inside biological safety cabinets (“hoods”) between uses.

Food and beverage protection

Since the FDA issued a rule in 2001 requiring that virtually all fruit and vegetable juice producers follow HACCP controls, and mandating a 5-log reduction in pathogens, UVGI has seen some use in sterilization of fresh juices such as fresh-pressed apple cider.



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Categories : Science and Industry Updates

The Septage Management System of the Baliwag Water District, Philippines – MyronLMeters.com

Posted by 23 Jan, 2013

TweetThe Municipality of Baliwag is located in the Province of Bulacan in the Philippines, just about an hour’s drive north of Metro Manila. The urban LGU has a population of over 160,000 and is the financial, commercial, and educational center of the Province of Bulacan, with the majority of these residents receiving their water supply – and soon their sanitation – […]

The Municipality of Baliwag is located in the Province of Bulacan in the Philippines, just about an hour’s drive north of Metro Manila. The urban LGU has a population of over 160,000 and is the financial, commercial, and educational center of the Province of Bulacan, with the majority of these residents receiving their water supply – and soon their sanitation – from the Baliwag Water District (BWD).

The BWD, like other water districts in the Philippines, is a government owned and controlled corporation (GOCC) focused on providing water and sanitation service on a baliwag1.JPGcost-recovery basis. Water districts around the country are coordinated by the Local Water Utilities Administration (LWUA), a unique GOCC itself that is tasked to promote and oversee the development of WatSan systems outside of the Metro Manila area.

In the Philippines, sewerage is rare / mainly non-existent outside of the Metro Manila area, with most residents in urban areas relying on septic tanks, most of which – in absence of any formal sanitation program – are often poorly designed and rarely desludged. This results in widespread groundwater contamination and polluted rivers from the discharges of septic tank effluent directly to drainage canals.

Awareness is rapidly rising around the country about the seriousness of this sanitation problem though, and a wide variety of both donor-driven and locally-driven sanitation programs are now underway, including a variety of septage management programs. However, to date, these existing septage management programs have been undertaken by the LGU/private sector (e.g. in San Fernando City, La Union), by an LGU-water district partnership (e.g. in Dumaguete City, Negros Oriental), or by a mainly private sector ‘build-operate-transfer’ style of arrangement (e.g. the programs of Manila Water Company Inc. & Maynilad Water Services Inc. in the Metro Manila area).

baliwag2.JPGThe BWD, though, decided to try a different arrangement with its new septage management program: one led entirely by the water district, with very little LGU/government collaboration. The BWD, led by its dynamic and learned General Manager since 1995, Mr Artemio Baylosis, has rapidly grown from an insignificant, 1000-connection provider to the significant and respected provider it is today, ISO-9001 certified and with over 25,000 connections accounting for about 80% of the total population of Baliwag, which is better coverage than many other water districts in other urban areas around the country.

Through the initiative of Mr Baylosis and the BWD team, the BWD, in 2008, secured the support of the USAID-funded Philippine Water Revolving Fund (PWRF) to fund a feasibility study on septage management for the water district. From the data and analysis gathered by this study, the BWD was then able to pursue their own program without any further donor assistance, the planning for which began in 2009.

The next step after the feasibility study was to ensure a suitable regulatory environment for the program. The BWD worked with the local government of Baliwag to help them pass an ordinance in 2009 that allowed the establishment of the BWD septage and (future) sewerage management program. This was not a particularly comprehensive nor proactive ordinance for the LGU, but was sufficient to allow the BWD to be proactive on their own initiative. In addition, the BWD and LGU signed an MoA in 2010 to provide further details on the sharing of responsibilities for the septage management program. Most of these responsibilities were taken on by the BWD, with the LGU simply in charge of levying fines where necessary and in supporting the outreach efforts of the BWD about the program.

The BWD then required a source of funds to manage this program. Rather than rely on donor assistance, the BWD simply secured a 60M Peso (~$1.5M USD) loan from thebaliwag3.JPG Philippine National Bank, with a 10-year repayment period and 7% interest.

With these funds, the BWD could then launch into the program planning and consultations. They conducted a thorough public information drive across the entire LGU, to discuss and seek feedback on the program’s legality, guidelines, and proposed tariff structure. During this time, the BWD also engaged in a ‘Water Operators Partnership’, through the USAID-sponsored Waterlinks program, which linked them up with Indah Water Company in Malaysia, for joint trainings, site visits, and consultations on technical aspects of Indah’s already successful program.

Through this, the BWD was able to design their program to incorporate elements already proven to be successful, and build off of the unsuccessful elements of other programs. On desludging, the BWD decided to split their service area into 5 zones, with the goal of desludging one zone each year, so as to achieve a regular, once-every-5-years desludging cycle for its customers. However, they also do not plan on charging any additional fees if customers want to avail of additional desludgings within this 5-year period; if they desire 2 or 3 desludgings during this time, the BWD hopes to be able to do this for them without any additional fee.

baliwag4.JPGThe BWD is able to make this offer because, unlike a private company, they do not need to make a profit, only to recover their costs. This also allows them to offer a low water tariff, with the subsidised price of the first 10 cubic meters at only ~145 Pesos (just over $3USD), with average monthly water consumption in the community at approximately 20 cubic meters. And because of their 80% water supply coverage, they thus decided to use this water tariff as the basis for financing their septage management costs. Their financial models determined that a fixed charge of 10% of the user’s total water bill would collect enough to recover the costs. Thus, the previously mentioned 145 Peso bill, as of June 2012, became a 160 Peso bill. The community was consulted on this tariff structure and were agreeable to it. So far, as of Dec. 2012, no one has complained about the new fee, even though the desludging service has not yet begun.

In addition to the desludging service that the BWD will offer, they also plan on taking responsibility for enforcing properly-designed septic tanks in the LGU, both for old tanks and new constructions. For the former, they hope to inspire maintenance/upgrading via consultation with customers and fines if necessary, while for the latter, they plan on visiting new construction sites to ensure that the septic tanks are properly designed. They have also already begun collecting data on every septic tank of their customers. Currently, they have just noted the number of household users of the tank and its general location on the property (e.g. on the left side / right side / inside / etc.), but they soon hope to begin mapping each of these tanks into their GIS/GPS database, for easy reference and route planning for desludging. Properly-designed septic tanks (i.e. 2 or 3 chambers and sealed at the bottom) are important, since many of the country’s existing tanks are sized too small for their daily flow rate and are not sealed at the bottom, resulting in widespread groundwater pollution.

A problem that has faced previous septage management programs is that of availment rates. Even if customers are paying (e.g. through the water tariff) for the desludging service, availment rates of this service have often been as low as 50%, due mainly to the desludgers’ rules about the lifting of the septic tank lid. In previous programs, the desludger required residents to lift the septic tank lid if they wanted to avail of the service (to avoid any liability related to potentially damaging the lid), but this was often complicated by the fact that many septic tanks here are built without a lid and/or are built in a difficult-to-access location, such as under the kitchen.

Learning from this, the BWD will try a different approach. In the first 5-year cycle, the BWD will lift all of the lids themselves, a day or two in advance of the planned baliwag5.JPGdesludging, and if there is no lid, the BWD will drill one themselves by breaking a hole through the floor. Then, in the second 5-year cycle, the customers will be responsible for lifting their own lids. They are not concerned about liability, as their activities are supported by the LGU’s ordinance, though it remains to be seen whether this will be enough to prevent any complaints on potential damage. If successful, though, this approach could greatly increase availment rates, and thus greatly reduce the amount of ground/surface water pollution from overflowing septic tanks.

Turning now to the technology, the BWD purchased two, 5 cubic meter desludging trucks (at a cost of 17.4M Pesos (~$420,000 USD), which they hope to run at 3 loads per day, 5 days per week. These trucks will bring the septage to the new septage treatment plant (SpTP), which is currently under construction in the LGU. The BWD purchased the land for this plant itself, even though the LGU is supposed to be legally obligated to provide it, thus showing the BWD’s desire to do it themselves. The construction of their SpTP and the office / laboratory building that will rise beside it were contracted out to two different local engineering companies. The SpTP will have a capacity of 30 cubic meters per day and will cost 32.7M Pesos (~$800,000 USD) to build. In addition to their regular desludging, the BWD also hopes that this capacity will allow the acceptance of some septage from neighboring LGUs or from small private desludgers, with a tipping fee applied. In theory, the site could also be upgraded to accept sewage one day, as they chose a location in a lower elevation area as compared with the rest of the LGU. The site is also strategically located in terms of odor – it is beside a smelly pig farm and duck farm, so it is unlikely that these neighbors will complain about odors from the plant!

baliwag6.JPGThe SpTP uses a highly mechanised technology package, which was chosen by the BWD so as to minimise the exposure of its staff to raw septage, even though this option is more expensive than a less mechanised version. Their technology process is as follows:

1) Macerator and/or bar screen – These will be able to run in series or parallel. The use of the macerator will depend on how much electricity it consumes.
2) A joint garbage screen / sand screen / FOG (fats/oils/grease) screen unit
3) Holding tank (with mixer) – 2 tanks, each with 2 days of holding time
4) Pump line, with cationic polymer injection, leading to the dewatering screw press (solids from this and the aforemention garbage / sand will fall into a pickup truck)
5) Equalisation Tank
6) Sequencing Batch Reactor (SBR) (Consisting of: a – Equalisation tank {aerobic} , b – SBR {aerobic} , c – Chlorine contact tank (Cl will drip in in liquid form), d – Effluent holding tank -> Discharge to storm drain. e – Sludge from tank B will get pumped to a sludge digestion tank, for further holding time, which will overflow back into tank A)

The aerobic portions are serviced by 2 blower motors. The site will also have 2 big water tanks for drinking water and recycled/rain water for use on site. The effluent can also be recirculated after the screw press back into the holding tank if so desired for further treatment time. The biosolids/sludge from this SpTP will be composted for local use around the LGU.

baliwag7.JPG

As of this writing (Dec. 2012), construction of the SpTP was nearly complete, with testing and commissioning to follow from Jan. to Aug. 2013, with the goal of project turn over and full operation by Sept. 2013. Even though it has not yet begun, the innovative design being used here by the BWD is already being mimicked by neighboring water districts in their septage planning, and it thus stands to serve as a model for water district-led septage management in the Philippines, with its lessons being applicable to septage management programs around the world as well.

MyronLMeters.com now features one-week direct shipping to the Philippines. Shipping one Ultrameter III 9P to the Philippines costs only $35 plus taxes and duties.

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Categories : Case Studies & Application Stories, Science and Industry Updates

Coming in 2013: The Myron L PoolPro PS9TK – MyronLMeters.com

Posted by 18 Jan, 2013

Tweet                            For Pool Professionals The PoolPro is a comprehensive high performance tool designed to simplify pool and spa water quality control for the pool professional. Both PoolPro models – the PS6 and the PS9TK feature innovative user-friendly features and functions that make […]

 

PoolPros

PoolPro PS9TK and PoolPro PS6

 

 

 

 

 

 

 

 

 

 

 

 

 

For Pool Professionals

The PoolPro is a comprehensive high performance tool designed to simplify pool and spa water quality control for the pool professional. Both PoolPro models – the PS6 and the PS9TK feature innovative user-friendly features and functions that make it easy to manage parameters critical to disinfection, water balance, system maintenance and compliance.

New! Fce FAC Readings

FCE function reports FAC quickly and accurately by measuring ORP, the chemical characteristic of chlorine that directly reflects its effectiveness, cross referenced with pH. Both DPD kits and colorimeters may tell the user the FAC value of the sample in the test tube, but since the chemistry of that sample is quite different from the source water being analyzed, the results are imprecisely related to actual disinfection power.

FCE function measures the real, unaltered chemistry of source water, including moment-to-moment changes in that chemistry.

FCE can be used for other types of oxidizing germicides and will track the effect of additives, such as cyanuric acid, that degrade chlorine effectively without changing the actual concentration of free available chlorine present.

In-Cell Titration Functions

The PS9TK adds the ability to perform in-cell conductometric titrations that provides a convenient way to determine alkalinity, hardness and LSI in the field. This eliminates the need to collect and transport samples to another location for analysis. User intuitive display prompts guide you through titration procedures from start to finish. All required reagents and equipment are included in the PS9 titration kit.

Water Balance Analysis

The PS9TK features both an LSI Calculator and an LSI Titration measurement mode. The Calculator allows you to perform what-if scenarios to predict how changes in solution parameters would affect the water balance of a system. The titration measurement function allows you to accurately calculate a saturation index value of a specific solution to determine whether the solution is balanced, scaling or corrosive.

Hardness Unit Conversion The Hardness and LSI Titrations and LSI Calculator functions allow you to set the hardness unit preference to either grains of hardness or ppm CaCO3 according to your needs.

System Validation & Calibration

The PoolPro provides a fast, precise, easy-to-use method of obtaining Oxidation Reduction Potential (ORP or REDOX) mV readings to check the true level of effectiveness of ALL sanitizers in any pool or spa. ORP objectively and precisely measures sanitizer ability to burn up, or oxidize, organic matter in the water. ORP can only be determined by an electronic instrument.

PoolPro ORP mV readings serve as a necessary check to ensure automatic ORP control systems are working properly. PoolPro also provides independent readings for recalibration and to detect system failure.

Saltwater Chlorine Generation

PoolPro provides a convenient one-touch test for Mineral/Salt concentration. This is ideal for saltwater systems where manual testing with separate instrumentation is necessary to ensure the proper amount of sodium chloride is present for chlorine generation in quantities specified for microbial disinfection. PoolPro can also be used to recalibrate equipment as part of regular maintenance.

Wireless Benefits

The optional bluDock™ accessory package is an integrated data solution for your record keeping requirements, eliminating the need for additional hardware, wires and hassle. Because the user never touches the data, there is little opportunity for data tampering and human error. bluDock software has an easy to use interface with user intuitive functions for storing, sorting and exporting data.

Simply the Best

PoolPro is lightweight, portable, buoyant, waterproof, easy-to-calibrate, and easy-to-use. Simply rinse and fill the cell cup by dipping the PoolPro in the water, then press the button of the parameter you wish to measure. You immediately get a standard, numerical digital readout — eliminating all subjectivity. And you can store up to 100 date-time-stamped readings in PoolPro’s non-volatile memory.

Watch for the product launch later this year.

 

Categories : Product Updates, Science and Industry Updates

Recent Papers in Water Treatment for Small/Decentralized Systems – MyronLMeters.com

Posted by 12 Jan, 2013

TweetRecent Papers in Water Treatment for Small/Decentralized Systems Content Table Recent Papers in Water Treatment for Small/Decentralized Systems  Turbidity and chlorine demand reduction using locally available physical water clarification mechanisms before household chlorination in developing countries Appropriate wastewater treatment systems for developing countries: criteria and indictor assessment in Thailand A new paradigm for low-cost urban […]

Recent Papers in Water Treatment for Small/Decentralized Systems

Content Table

Turbidity and chlorine demand reduction using locally available physical water clarification mechanisms before household chlorination in developing countries

Journal of Water and Health Vol 07 No 3 pp 497–506 © IWA Publishing 2009 doi:10.2166/wh.2009.071

Link to Summary Page

Nadine Kotlarz, Daniele Lantagne, Kelsey Preston and Kristen Jellison

Department of Civil and Environmental Engineering, Lehigh University, 13 East Packer Avenue, Bethlehem, PA 18015, USA
Enteric Diseases Epidemiology Branch, US Centers for Disease Control and Prevention, 1600 Clifton Road, MS-A38, Atlanta, GA 30333, USA Tel.:             +1 404 639 0231       Fax: +1 404 639 2205 E-mail: dlantagne@cdc.gov

Abstract

Over 1.1 billion people in the world lack access to improved drinking water. Diarrhoeal and other waterborne diseases cause an estimated 1.9 million deaths per year. The Safe Water System (SWS) is a proven household water treatment intervention that reduces diarrhoeal disease incidence among users in developing countries. Turbid waters pose a particular challenge to implementation of SWS programmes; although research shows that a 3.75 mg l-1 sodium hypochlorite dose effectively treats turbid waters, users sometimes object to the strong chlorine taste and prefer to drink water that is more aesthetically pleasing. This study investigated the efficacy of three locally available water clarification mechanisms—cloth filtration, settling/decanting and sand filtration—to reduce turbidity and chlorine demand at turbidities of 10, 30, 70, 100 and 300 NTU. All three mechanisms reduced turbidity (cloth filtration -1–60%, settling/decanting 78–88% and sand filtration 57–99%). Sand filtration (P=0.002) and settling/decanting (P=0.004), but not cloth filtration (P=0.30), were effective at reducing chlorine demand compared with controls. Recommendations for implementing organizations based on these results are discussed.

Appropriate wastewater treatment systems for developing countries: criteria and indictor assessment in Thailand

Water Science & Technology—WST Vol 59 No 9 pp 1873–1884 © IWA Publishing 2009 doi:10.2166/wst.2009.215

Link to Summary Page

W. Singhirunnusorn and M. K. Stenstrom

Faculty of Environment and Resource Studies, Mahasarakham University, Kantharawichai District, Maha Sarakham Province 44150, Thailand E-mail: swichitra@gmail.com
Department of Civil and Environmental Engineering, UCLA, Los Angeles CA 90095, USA E-mail: stenstro@seas.ucla.edu

Abstract

This paper presents a comprehensive approach with factors to select appropriate wastewater treatment systems in developing countries in general and Thailand in particular. Instead of focusing merely on the technical dimensions, the study integrates the social, economic, and environmental concerns to develop a set of criteria and indicators (C&I) useful for evaluating appropriate system alternatives. The paper identifies seven elements crucial for technical selection: reliability, simplicity, efficiency, land requirement, affordability, social acceptability, and sustainability. Variables are organized into three hierarchical elements, namely: principles, criteria, and indicators. The study utilizes a mail survey to obtain information from Thai experts—academicians, practitioners, and government officials—to evaluate the C&I list. Responses were received from 33 experts on two multi-criteria analysis inquiries—ranking and rating—to obtain evaluative judgments. Results show that reliability, affordability, and efficiency are among the most important elements, followed by sustainability and social acceptability. Land requirement and simplicity are low in priority with relatively inferior weighting. A number of criteria are then developed to match the contextual environment of each particular condition. A total of 14 criteria are identified which comprised 64 indicators. Unimportant criteria and indicators are discarded after careful consideration, since some of the indicators are local or site specific.

A new paradigm for low-cost urban water supplies and sanitation in developing countries

Water Policy Vol 10 No 2 pp 119–129 © IWA Publishing 2008 doi:10.2166/wp.2008.034

Link to Summary Page

Duncan Maraa and Graham Alabasterb

aCorresponding author. School of Civil Engineering, University of Leeds, Leeds LS2 9JT UK. Fax: +44-113-343-2243 E-mail: d.d.mara@leeds.ac.uk
bUnited Nations Human Settlements Programme, PO Box 30300, Nairobi, Kenya

Abstract

To achieve the Millennium Development Goals for urban water supply and sanitation ~300,000 and ~400,000 people will have to be provided with an adequate water supply and adequate sanitation, respectively, every day during 2001–2015. The provision of urban water supply and sanitation services for these numbers of people necessitates action not only on an unprecedented scale, but also in a radically new way as “more of the same” is unlikely to achieve these goals. A “new paradigm” is proposed for low-cost urban water supply and sanitation, as follows: water supply and sanitation provision in urban areas and large villages should be to groups of households, not to individual households. Groups of households would form (even be required to form, or pay more if they do not) water and sanitation cooperatives. There would be standpipe and yard-tap cooperatives served by community-managed sanitation blocks, on-site sanitation systems or condominial sewerage, depending on space availability and costs and, for non-poor households, in-house multiple-tap cooperatives served by condominial sewerage or, in low-density areas, by septic tanks with on-site effluent disposal. Very poor households (those unable to afford to form standpipe cooperatives) would be served by community-managed standpipes and sanitation blocks.

Faecal bacterial indicators removal in various wastewater treatment plants located in Almendares River watershed (Cuba)

Water Science & Technology—WST Vol 58 No 4 pp 773–779 © IWA Publishing 2008 doi:10.2166/wst.2008.440

Link to Summary Page

Tamara Garcia-Armisen, Josué Prats, Yociel Marrero and Pierre Servais

Ecologie des Systèmes Aquatiques, Université Libre de Bruxelles, Brussels, Belgium *Present address: MINT, Vrije Universiteit Brussel, Building E, Pleinlaan 2, 1050, Brussels, Belgium Tel.:            +3226291918       E-mail: tgarciaa@vub.ac.be
Dpto. de Microbiología, Facultad de Biología, Universidad de La Habana, La Habana, Cuba
Instituto Superior Politécnico José Antonio Echeverría, La Habana, Cuba

Abstract

The Almendares River, located in Havana city, receives the wastewaters of more than 200,000 inhabitants. The high abundance of faecal bacterial indicators (FBIs) in the downstream stretch of the river reflects the very poor microbiological water quality. In this zone, the Almendares water is used for irrigation of urban agriculture and recreational activities although the microbiological standards for these uses are not met. Improvement of wastewater treatment is absolutely required to protect the population against health risk. This paper compares the removal of FBIs in three wastewater treatment plants (WWTPs) located in this watershed: a conventional facility using trickling filters, a constructed wetland (CW) and a solar aquatic system (SAS). The results indicate better removal efficiency in the two natural systems (CW and SAS) for all the measured parameters (suspended matters, biological oxygen demand, total coliforms, E. coli and enterococci). Removals of the FBIs were around two log units higher in both natural systems than in the conventional one. A longitudinal profile of the microbiological quality of the river illustrates the negative impact of the large conventional WWTP. This case study confirms the usefulness of small and natural WWTPs for tropical developing countries, even in urban and periurban areas.

Treatment of low and medium strength sewage in a lab-scale gradual concentric chambers (GCC) reactor

Water Science & Technology—WST Vol 57 No 8 pp 1155–1160 © IWA Publishing 2008 doi:10.2166/wst.2008.093

Link to Summary Page

L. Mendoza, M. Carballa, L. Zhang and W. Verstraete

Experimental Reproduction Centre (CEYSA), Agricultural Faculty, Technical University of Cotopaxi, Latacunga, Ecuador E-mail: lauramen_2000@yahoo.com
Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, B-9000, Ghent, Belgium E-mail: willy.verstraete@ugent.be; marta.carballa@ugent.be; lezhanghua@hotmail.com

Abstract

One of the major challenges of anaerobic technology is its applicability for low strength wastewaters, such as sewage. The lab-scale design and performance of a novel Gradual Concentric Chambers (GCC) reactor treating low (165±24 mg COD/L) and medium strength (550 mg COD/L) domestic wastewaters were studied. Experimental data were collected to evaluate the influence of chemical oxygen demand (COD) concentrations in the influent and the hydraulic retention time (HRT) on the performance of the GCC reactor. Two reactors (R1 and R2), integrating anaerobic and aerobic processes, were studied at ambient (26°C) and mesophilic (35°C) temperature, respectively. The highest COD removal efficiency (94%) was obtained when treating medium strength wastewater at an organic loading rate (OLR) of 1.9 g COD/L·d (HRT = 4 h). The COD levels in the final effluent were around 36 mg/L. For the low strength domestic wastewater, a highest removal efficiency of 85% was observed, producing a final effluent with 22 mg COD/L. Changes in the nutrient concentration levels were followed for both reactors.

Use of modelling for optimization and upgrade of a tropical wastewater treatment plant in a developing country

Water Science & Technology Vol 56 No 7 pp 21–31 © IWA Publishing 2007 doi:10.2166/wst.2007.675

Link to Summary Page

D. Brdjanovic*, M. Mithaiwala** , M.S. Moussa*** , G. Amy* and M.C.M. van Loosdrecht**** 

*Department of Urban Water and Sanitation, UNESCO-IHE Institute for Water Education, Westvest 7, PO Box 3015, 2061 DA , Delft, The Netherlands (E-mail: d.brjanovic@unesco-ihe.org)
**Drainage Department, Surat Municipal Corporation, Muglisara, Surat , Gujarat, 395003, India (Email: mayank_heena6143@yahoo.com)
***Civil Engineering Department, Faculty of Engineering Mataria, Helwan , University, Egypt (Email: m.moussa@delft-environment.com)
****Department of Biochemical Engineering, Delft University of Technology, Julianalaan 67, 2628 BC , Delft, The Netherlands (Email: m.c.m.vanloosdrecht@tudelft.nl)

Abstract

This paper presents results of a novel application of coupling the Activated Sludge Model No. 3 (ASM3) and the Anaerobic Digestion Model No.1 (ADM1) to assess a tropical wastewater treatment plant in a developing country (Surat, India). In general, the coupled model was very capable of predicting current plant operation. The model proved to be a useful tool in investigating various scenarios for optimising treatment performance under present conditions and examination of upgrade options to meet stricter and upcoming effluent discharge criteria regarding N removal. It appears that use of plant-wide modelling of wastewater treatment plants is a promising approach towards addressing often complex interactions within the plant itself. It can also create an enabling environment for the implementations of the novel side processes for treatment of nutrient-rich, side-streams (reject water) from sludge treatment.

Ceramic silver-impregnated pot filters for household drinking water treatment in developing countries: material characterization and performance study

Water Science & Technology: Water Supply Vol 7 No 5-6 pp 9–17 © IWA Publishing 2007 doi:10.2166/ws.2007.142

Link to Summary Page

D. van Halem*, S.G.J. Heijman* , A.I.A. Soppe** , J.C. van Dijk* and G.L. Amy*** 

*Delft University of Technology, Stevinweg 1, 2628 CN , Delft, The Netherlands (E-mail: d.vanhalem@tudelft.nl; j.c.vandijk@tudelft.nl)
**Delft University of Technology & Kiwa Water Research, Groningenhaven 7, 3433 PE , Nieuwegein, The Netherlands (E-mail: s.g.j.heijman@tudelft.nl)
***Aqua for All Foundation, Groningenhaven 7, 3433 PE , Nieuwegein, The Netherlands (E-mail: gsoppe@planet.nl)
****UNESCO-IHE Institute for Water Education, Westvest 7, 2611 AX , Delft, The Netherlands (E-mail: g.amy@unesco-ihe.org)

Abstract

The ceramic silver-impregnated pot filter (CSF) is a low-cost drinking water treatment system currently produced in many factories worldwide. The objective of this study is to gather performance data to provide a scientific basis for organisations to safely scale-up and implement the CSF technology. Filters from three production locations are included in this study: Cambodia, Ghana and Nicaragua. The microstructure of the filter material was studied using mercury intrusion porosimetry and bubble-point tests. Effective pores were measured with a mean of 40 mm, which is larger than many pathogenic microorganisms. The removal efficiency of these microorganisms was measured by using indicator organisms; total coliforms naturally present in canal water, sulphite reducing Clostridium spores, E.coli K12 and MS2 bacteriophages. The removal of these organisms was monitored during a long-term study of several months in the laboratory. Ceramic silver impregnated pot filters successfully removed total coliforms and sulphite reducing Clostridium spores. High concentrations of Escherichia coli K12 were also removed, with log(10) reduction values consistently higher than 2. MS2 bacteriophages were only partially removed from the water, with significantly better results for filters without an impregnation of colloidal silver. During this study the main deficiency of the filter system proved to be the low water production; after 12 weeks of use all filter discharges were below 0.5 Lh-1, which is insufficient to provide drinking water for a family

Ceramic membranes for direct river water treatment applying coagulation and microfiltration

Water Science & Technology: Water Supply Vol 6 No 4 pp 89–98 © IWA Publishing 2006 doi:10.2166/ws.2006.906

Link to Summary Page

A. Loi-Brügger*, S. Panglisch*, P. Buchta*, K. Hattori**, H. Yonekawa**, Y. Tomita** and R. Gimbel*,***

*IWW Water Center, Moritzstr. 26, 45476 Mülheim, , Germany (E-mail: a.loi@iww-online.de)
**NGK Insulators Ltd., 2-56 Suda-cho, Nagoya, Aichi, , 467-8530, Japan (E-mail: kohji-h@ngk.co.jp)
***Institut für Energie- und Umweltverfahrenstechnik, Universität Duisburg-Essen Bismarckstr. 90, 47057 Duisburg, , Germany (E-mail: gimbel@uni-duisburg.de)

Abstract

A new ceramic membrane has been designed by NGK Insulators Ltd., Japan, to compete in the drinking water treatment market. The IWW Water Centre, Germany, investigated the operational performance and economical feasibility of this ceramic membrane in a one year pilot study of direct river water treatment with the hybrid process of coagulation and microfiltration. The aim of this study was to investigate flux, recovery, and DOC retention performance and to determine optimum operating conditions of NGK’s ceramic membrane filtration system with special regards to economical aspects. Temporarily, the performance of the ceramic membrane was challenged under adverse conditions. During pilot plant operation river water with turbidities between 3 and 100 FNU was treated. Membrane flux was increased stepwise from 80–300 l/m2h resulting in recoveries between 95.9 and 98.9%. A DOC removal between about 20–35% was achieved. The pilot study and the subsequent economical evaluation showed the potential to provide a reliable and cost competitive process option for water treatment. The robustness of the ceramic membrane filtration process makes it attractive for a broad range of water treatment applications and, due to low maintenance requirements, also suitable for drinking water treatment in developing countries.

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Water Services Management and Governance – Tapio Katko, Petri S. Juuti, and Klaas Schwartz
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Categories : Case Studies & Application Stories, Science and Industry Updates

Reverse osmosis biofouling: Impact of feed channel spacer and biofilm development in spacer-filled channels – MyronLMeters.com

Posted by 9 Jan, 2013

TweetIntroduction Water desalination via reverse osmosis (RO) technology provides a solution to the world’s water shortage problem. Until now, the production of fresh water from seawater has reached 21-million cubic meter per day all around the world (Wangnick, 2005). However, the success of RO technology is subject to improvement as the technology is challenged by […]

Introduction

Water desalination via reverse osmosis (RO) technology provides a solution to the world’s water shortage problem. Until now, the production of fresh water from seawater has reached 21-million cubic meter per day all around the world (Wangnick, 2005). However, the success of RO technology is subject to improvement as the technology is challenged by a biofouling problem –a problem related to biological material development which forms a sticky layer on the membrane surface (Flemming, 1997; Baker and Dudley, 1998).

Continuous biofouling problems in RO lead to higher energy input requirement as an effect of increased biofilm resistance (Rf) and biofilm enhanced osmotic pressure (BEOP), lower quality of product water due to concentration polarization (CP) – increased concentration due to solutes accumulation on the membrane surface, (Herzberg and Elimelech, 2007), and thus significant increase in both operating and maintenance costs.

Recent studies and objectives

Recent studies show the importance of the operating conditions (e.g. flux and cross flow velocities) in RO biofouling. The presence of feed channel spacers has also been getting more attention as it may have adverse effects. A previous study (Chong et al., 2008) without feed channel spacers showed that RO biofouling was a flux driven process where higher flux increased fouling rate. It was also shown that biofouling caused a BEOP effect due to elevated CP of solutes at the membrane surface, thus resulted in loss of driving force. The BEOP effect was more severe at high flux and low crossflow operation.

In another recent study (Vrouwenvelder et al., 2009a) involving feed channel spacers suggested that flux did not affect fouling and biofouling was more severe when the crossflow velocity was higher. However, these studies were conducted on river water at low level of salinity and under no/very low flux conditions, which may suggested that BEOP effect was not observed in the above studies. These contradictory observations relating to the biofouling process in RO need to be systematically addressed as it is critical to understand the mechanism for sustainable operation of RO technology.

The objective of this study was to observe the impact of spacer towards RO biofouling as well as to investigate the development of biofilm in a spacer filled channel. The experiments were conducted at constant flux and biofouling was observed by the increase of transmembrane pressure (TMP). Observation with confocal light scanning microscope (CLSM) method was conducted to the fouled membrane and spacers to provide information of biofilm development inside the membrane module.

Materials and methods

A lab-scale set-up was arranged to resemble the real RO operation where experiments were performed with elevated salinity, high pressure, imposed flux, and permeation. The schematic diagram of the set-up is depicted in Figure 1. It is a fully-recycled system with two identical RO modules running in series. Feed solution contained constant amounts NaCl and nutrient broth (NB) to provide sufficient TOC level.

The study was conducted in the constant flux mode and biofouling was measured via the rise in TMP. A mass-flow controller was installed at the permeate side to maintain the amount of permeate withdrawn. A bacteria solution was injected into the system before the feed solution entered the RO modules and a set of microfilters (5 μm and 0.2 μm) were installed at downstream to prevent excess bacteria from entering the feed tank and turning the feed tank into an “active bioreactor”.

reverseos1.jpg

Model bacteria Pseudomonas aeruginosa (PAO1) was used in the experiment. Bacteria stock solution used in the biofouling tests was prepared in batch and the stock solution was replenished every 24 hours. Bacteria were grown in mixture of NB and NaCl solution where they were harvested after 24 hours and diluted into autoclaved salt solution. The concentration of bacteria was controlled and measured by optical density (OD) using UV spectrophotometer at 600 nm. Batch prepared bacteria stock solution has some advantages over using continuous feed from a chemostat (Chong et al., 2008). A more consistent and fresh bacteria load and without excess nutrient was introduced into the system as nutrient content was completely removed in the harvesting step.

Prior to every experiment, cut RO membranes (DOW Filmtec, BW-30) were soaked in Milli-Q water and sterilized in 70% ethanol solution. Similar pretreatment procedures were applied to membrane support layers and feed channel spacers prior every experiment. The spacers used in the experiments are obtained from unused Hydranautics LFC-1 spiral wound module (Figure 2).

reverseos2.jpg

The membranes were compacted at a maximum flux (~65 L/m2.h) overnight with Milli-Q water until a stable flux was achieved. Following compaction, the flux was set to the desired values and NaCl solution was added into the feed tank until the desired concentration was achieved. The system was let to mix for 1.5 hours. NB solution was then added into the feed tank to provide an average background nutrient concentration of 6.5 mg/L TOC. The system was allowed to well-mix for 1.5 hours.

The biofouling test was initiated by continuous injection of bacteria stock solution into the flow line at a dilution rate of 1:500 based on RO cross-flow rate. Biofilm was allowed to grow on the RO membranes. TMP rise due to biofouling was measured over time. The solution in the feed tank was removed and replaced with a fresh solution at the same NaCl and NB concentration twice per day in order to maintain the freshness level of the feed solution.

Upon completion of the fouling test, the RO system was cleaned with:
 Tap water adjusted to pH 2 with HNO3 for 1.5 hours
 Tap water adjusted to pH 11 with NaOH for 1.5 hours
 Flowing tap water for rinsing for 1.5 hours
 Final rinsing with Milli-Q water at unadjusted pH

The fouled membranes were removed from the RO cells for membrane autopsy. In this analysis, fluorescence staining methods and confocal laser scanning microscope (CLSM) were used to detect the biofilm.

Biofilms were prepared for CLSM by staining with the LIVE/DEAD BacLight Bacterial Viability Kits (Molecular Probes, L7012). It consists of SYTO 9 green-fluorescent nucleic acid stain and the red-fluorescent nucleic acid stain, propidium iodide (PI). These stains possess different spectral characteristics and different ability to penetrate healthy bacterial cells. When used alone, the SYTO 9 stain generally labels all bacteria in a population — those with intact and damaged membranes. In contrast, propidium iodide penetrates only bacteria with damaged membranes, causing a reduction in the SYTO 9 stain fluorescence when both dyes are present. Thus, with an appropriate mixture of the SYTO 9 and propidium iodide stains, bacteria with intact cell membranes stain fluorescent green, whereas bacteria with damaged membranes stain fluorescent red.

Microscopic observation and image acquisition of biofilms were performed using a confocal laser scanning microscope (ZEISS, model LSM710), equipped with Argon laser at 488 nm and DPSS561-10 laser at 561 nm. Images were captured using confocal microscope bundled program ZEN 2009.

Results and discussions

The cross-flow velocity (CFV) in RO membrane operations is known to affect fouling rate. At higher CFV, the flow causes scouring effects which results in slower fouling (Koltuniewicz et al., 1995). On the other hand, experiments of RO modules without the presence of flux shows that a higher cross-flow velocity may increase biofouling due to more nutrients supply (Vrouwenvelder et al., 2009b).

In our study, the investigation was carried out by varying the cross-flow velocity (CFV) from
0.1, 0.17, to 0.34 m/s. The NaCl concentration used was constant at 2000 mg/L and the applied flux was constant at 35 LMH. TMP values were measured overtime and normalized to the initial TMP.

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Figure 3 shows the normalized TMP profiles. Faster TMP rise was observed at lower CFV and both operation with and without spacer show similar profiles. The delay of TMP rise caused by spacer was quantified by measuring the time needed for the TMP to increase by 10 % (Table 1). The effect of spacer was higher at higher CFV where the percentage of the delay was 21.21 % and 42.87 % at 0.10 m/s and 0.17 m/s respectively. An interesting phenomenon was observed during the earlier TMP rise (0-3 days) where change in CFV gives little effect on TMP profiles. Similar phenomenon was observed for operation with and without spacer. A possible explanation for this phenomenon is that during this period bacterial attachment was dominant and therefore operation at constant flux gives similar initial TMP rise. Previous studies (Chong et al., 2008) have shown previously that membrane biofouling is a flux driven process where higher flux increases the TMP rise. However, their study did not include spacers and did not focus on initial TMP rise.

Table 1. The delay of biofouling rate caused by spacer at different CFV

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The effect of different salt concentrations was also investigated. In this experiment the flux and CFV were fixed at 35 LMH and 0.17 m/s respectively. Figure 4 shows the normalized TMP profile of three different NaCl concentrations in the feed solution. When the feed channel spacer was absent it was very obvious that faster TMP rise was observed at higher salt concentration. This suggests that the effect of concentration polarization (CP) increases with the salt concentration and confirms the presence of the biofilm enhanced osmotic pressure (BEOP) effect (Herzberg and Elimelech, 2007; Chong et al., 2008). This phenomenon however, was less obvious when the spacer was present on the membrane. The spacer appears to provide flow eddies thus reducing the effect of CP and to be useful to prevent biofouling on the membrane which was indicated with slower TMP rise. The spacer gives bigger effect at higher salt concentration where the time to reach 10 % TMP rise was delayed by 30 % at 100 mg/L and 2000 mg/L NaCl, and 95.7 % at 4000 mg/L (Table 2).

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4.2 Biofilm development in spacer-filled RO membrane channel The development of biofilm in spacer-filled channel was observed via microscopic and microscopic method. Macroscopic images are to show overall uniformity of biofilm distribution, while the microscopic images are able to show a more detailed biofilm patterns. All of the images in this study were taken from separate experiments as the samples were unable to be reused after analysis, however all the conditions for the experiments were maintained the same.

Figure 5 shows the macroscopic images of biofilm development. The biofilm sample on the membranes and spacers were stained with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) dye. CTC stains bacteria with respiration activity and stained cells appear in red colour. Analysis was done after 0, 3, 6, and 10 days, the condition was 35 LMH flux, 0.17 m/s CFV, and 4000 mg/L NaCl concentration. Longer experiment duration gives thicker and denser biofilm, which can be seen from higher red colour intensity. The biofilms have also shown overall uniformity across the membrane area where similar patterns were observed among each spacer squares.

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Figure 5. Macroscopic images of biofilm development on membranes and spacers. (A) 0-day, (B) 3-day, (C) 6-day, (D) 10-day. Biofilms stained with CTC dye and images taken with SONY NEX-5 digital camera.

Confocal laser scanning microscope (CLSM) provides a more detailed analysis of biofilm development (Figure 6). Based on the images, it appears that biofilm was initiated on the membrane; it later covered more areas and started to appear on the spacer. Areas behind the attached filaments of the spacer fiber seem to be suitable for the initial bacterial attachments rather than the centre of the spacer. Biofilm build-up observed on areas under the detached filaments was caused by higher shear due to accelerated CFV. Our experiments confirmed that biofouling in RO is a flux driven process. A lower TMP rise was observed at lower flux, which means slower biofouling rate. This is also supported with the biofilm coverage data where less coverage was observed at lower flux.

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Conclusions

From the findings above, several conclusions can be drawn. The hydrodynamic condition of the flow is affecting the biofouling process. Cross flow velocity (CFV) is an important parameter and lower fouling can be achieved at higher CFV. Having feed channel spacers on the membrane is advantageous as it provides a more well-mixed flow, reduces concentration polarization and reduces TMP increase. Biofilm enhanced osmotic pressure (BEOP) was another phenomenon observed in this study. Due to the BEOP effect, a faster TMP rise was achieved at higher salinity. However, with the presence of the spacer the BEOP effect was reduced significantly.

From our microscopic analysis of biofilm shows that initial bacterial deposition and biofilm development was started on the membrane especially on areas behind the attached spacer filaments. Biofilm develops over time to cover more areas and starts to grow on the spacer at the later stages. Imposed flux also influences the biofilm development where lower biofouling is achieved at lower flux.

References

Baker, J. S. and Dudley, L. Y. (1998), “Biofouling in membrane systems – a review”, Desalination, Vol. 118, No. 1-3, pp. 81-90.

Chong, T. H., Wong, F. S. and Fane, A. G. (2008), “The effect of imposed flux on biofouling in reverse osmosis: Role of concentration polarisation and biofilm enhanced osmotic pressure phenomena”, Journal of Membrane Science, Vol. 325, No. 2, pp. 840-850.

Flemming, H. C. (1997), “Reverse osmosis membrane biofouling”, Experimental Thermal and Fluid Science, Vol. 14, No. 4, pp. 382-391.

Herzberg, M. and Elimelech, M. (2007), “Biofouling of reverse osmosis membranes: Role of biofilm-enhanced osmotic pressure”, Journal of Membrane Science, Vol. 295, No. 1-2, pp.
11-20.

Koltuniewicz, A. B., Field, R. W. and Arnot, T. C. (1995), “Cross-flow and dead-end microfiltration of oily-water emulsion. Part I: Experimental study and analysis of flux decline”, Journal of Membrane Science, Vol. 102, No. 1-3, pp. 193-207.

Suwarno, S. R., Puspitasari, V. L., Chong, T. H., Fane, A. G., Chen, X., Rice, S. A., Mcdougald, D. and Cohen, Y. (2010) “The hydrodynamic effect on biofouling in reverse osmosis membrane processes”, IWA International Young Water Professionals Conference, Sydney,

Vrouwenvelder, J. S., Hinrichs, C., Van Der Meer, W. G., Van Loosdrecht, M. C. and Kruithof, J. C. (2009b), “Pressure drop increase by biofilm accumulation in spiral wound RO and NF membrane systems: role of substrate concentration, flow velocity, substrate load and flow direction”, Biofouling, Vol. 25, No. 6, pp. 543-555.

Wangnick (2005), 2004 Worldwide Desalting Plants Directory, Global Water Intelligence, Oxford, England.

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Categories : Science and Industry Updates

Desalination

Posted by 9 Dec, 2012

TweetDesalination refers to processes that remove some amount of salt and other minerals from saline water. Salt water is desalinated to produce fresh water suitable for human consumption or irrigation. One potential byproduct of desalination is salt. Desalination is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused […]

Desalination refers to processes that remove some amount of salt and other minerals from saline water.

Salt water is desalinated to produce fresh water suitable for human consumption or irrigation. One potential byproduct of desalination is salt. Desalination is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused on developing cost-effective ways of providing fresh water for human use. Along with recycled wastewater, this is one of the few rainfall-independent water sources.

Large-scale desalination typically uses large amounts of energy and specialized, expensive infrastructure, making it more expensive than fresh water from conventional sources, such as rivers or groundwater.

Desalination is particularly relevant to countries such as Australia, which traditionally have relied on collecting rainfall behind dams to provide their drinking water supplies.

According to the International Desalination Association, in 2009, 14,451 desalination plants operated worldwide, producing 59.9e6 cubic meters (2.12×109 cu ft) per day, a year-on-year increase of 12.3%. It was 68 million m3 in 2010, and expected to hit 120 million m3 by 2020; some 40 million m3 is planned for the Middle East. The world’s largest desalination plant is the Jebel Ali Desalination Plant (Phase 2) in the United Arab Emirates.

 

 

 

 

Schematic of a multistage flash desalinator

A – steam in

B – seawater in

C – potable water out

D – waste out

E – steam out

F – heat exchange

G – condensation collection

H – brine heater

 

 

 

 

 

 

 

Plan of a typical reverse osmosis desalination plant

The traditional process used in these operations is vacuum distillation—essentially the boiling of water at less than atmospheric pressure and thus a much lower temperature than normal. This is because the boiling of a liquid occurs when the vapor pressure equals the ambient pressure and vapor pressure increases with temperature. Thus, because of the reduced temperature, energy is saved. Multistage flash distillation, a leading method, accounted for 85% of production worldwide in 2004.

The principal competing processes use membranes to desalinate, principally applying reverse osmosis technology. Membrane processes use semipermeable membranes and pressure to separate salts from water. Reverse osmosis plant membrane systems typically use less energy than thermal distillation, which has led to a reduction in overall desalination costs over the past decade. Desalination remains energy intensive, however, and future costs will continue to depend on the price of both energy and desalination technology.

Cogeneration

Cogeneration is the process of using excess heat from power production to accomplish another task. For desalination, cogeneration is the production of potable water from seawater or brackish groundwater in an integrated, or “dual-purpose”, facility in which a power plant becomes the source of energy for desalination. Alternatively, the facility’s energy production may be dedicated to the production of potable water (a stand-alone facility), or excess energy may be produced and incorporated into the energy grid (a true cogeneration facility). Cogeneration takes various forms, and theoretically any form of energy production could be used. However, the majority of current and planned cogeneration desalination plants use either fossil fuels or nuclear power as their source of energy. Most plants are located in the Middle East or North Africa, which use their petroleum resources to offset limited water resources. The advantage of dual-purpose facilities is they can be more efficient in energy consumption, thus making desalination a more viable option for drinking water.

 

 

 

 

 

 

 

The Shevchenko BN350, a nuclear-heated desalination unit

In a December 26, 2007, opinion column in The Atlanta Journal-Constitution, Nolan Hertel, a professor of nuclear and radiological engineering at Georgia Tech, wrote, “… nuclear reactors can be used … to produce large amounts of potable water. The process is already in use in a number of places around the world, from India to Japan and Russia. Eight nuclear reactors coupled to desalination plants are operating in Japan alone … nuclear desalination plants could be a source of large amounts of potable water transported by pipelines hundreds of miles inland…”

Additionally, the current trend in dual-purpose facilities is hybrid configurations, in which the permeate from a reverse osmosis desalination component is mixed with distillate from thermal desalination. Basically, two or more desalination processes are combined along with power production. Such facilities have already been implemented in Saudi Arabia at Jeddah and Yanbu.

A typical aircraft carrier in the US military uses nuclear power to desalinate 400,000 US gallons (1,500,000 l; 330,000 imp gal) of water per day.

Economics

Factors that determine the costs for desalination include capacity and type of facility, location, feed water, labor, energy, financing, and concentrate disposal. Desalination stills now control pressure, temperature and brine concentrations to optimize efficiency. Nuclear-powered desalination might be economical on a large scale.

While noting costs are falling, and generally positive about the technology for affluent areas in proximity to oceans, a 2004 study argued, “Desalinated water may be a solution for some water-stress regions, but not for places that are poor, deep in the interior of a continent, or at high elevation. Unfortunately, that includes some of the places with biggest water problems.”, and, “Indeed, one needs to lift the water by 2,000 meters (6,600 ft), or transport it over more than 1,600 kilometers (990 mi) to get transport costs equal to the desalination costs. Thus, it may be more economical to transport fresh water from somewhere else than to desalinate it. In places far from the sea, like New Delhi, or in high places, like Mexico City, high transport costs would add to the high desalination costs. Desalinated water is also expensive in places that are both somewhat far from the sea and somewhat high, such as Riyadh and Harare. In many places, the dominant cost is desalination, not transport; the process would therefore be relatively less expensive in places like Beijing, Bangkok, Zaragoza, Phoenix, and, of course, coastal cities like Tripoli.”[15] After being desalinated at Jubail, Saudi Arabia, water is pumped 200 miles (320 km) inland through a pipeline to the capital city of Riyadh. For coastal cities, desalination is increasingly viewed as an untapped and unlimited water source.

In Israel as of 2005, desalinating water costs US$ 0.53 per cubic meter. As of 2006, Singapore was desalinating water for US$ 0.49 per cubic meter.[18] The city of Perth began operating a reverse osmosis seawater desalination plant in 2006, and the Western Australian government announced a second plant will be built to serve the city’s needs.[19] A desalination plant is now operating in Australia’s largest city, Sydney,[20] and the Wonthaggi desalination plant was under construction in Wonthaggi, Victoria.

The Perth desalination plant is powered partially by renewable energy from the Emu Downs Wind Farm. A wind farm at Bungendore in New South Wales was purpose-built to generate enough renewable energy to offset the Sydney plant’s energy use,[22] mitigating concerns about harmful greenhouse gas emissions, a common argument used against seawater desalination.

In December 2007, the South Australian government announced it would build a seawater desalination plant for the city of Adelaide, Australia, located at Port Stanvac. The desalination plant was to be funded by raising water rates to achieve full cost recovery. An online, unscientific poll showed nearly 60% of votes cast were in favor of raising water rates to pay for desalination.

A January 17, 2008, article in the Wall Street Journal stated, “In November, Connecticut-based Poseidon Resources Corp. won a key regulatory approval to build the $300 million water-desalination plant in Carlsbad, north of San Diego. The facility would produce 50,000,000 US gallons (190,000,000 l; 42,000,000 imp gal) of drinking water per day, enough to supply about 100,000 homes … Improved technology has cut the cost of desalination in half in the past decade, making it more competitive … Poseidon plans to sell the water for about $950 per acre-foot [1,200 cubic metres (42,000 cu ft)]. That compares with an average [of] $700 an acre-foot [1200 m³] that local agencies now pay for water.”  Each $1,000 per acre-foot works out to $3.06 for 1,000 gallons, or $.81 per cubic meter.

While this regulatory hurdle was met, Poseidon Resources is not able to break ground until the final approval of a mitigation project for the damage done to marine life through the intake pipe is received, as required by California law. Poseidon Resources has made progress in Carlsbad, despite an unsuccessful attempt to complete construction of Tampa Bay Desal, a desalination plant in Tampa Bay, FL, in 2001. The Board of Directors of Tampa Bay Water was forced to buy Tampa Bay Desal from Poseidon Resources in 2001 to prevent a third failure of the project. Tampa Bay Water faced five years of engineering problems and operation at 20% capacity to protect marine life, so stuck to reverse osmosis filters prior to fully using this facility in 2007.

In 2008, a San Leandro, California company (Energy Recovery Inc.) was desalinating water for $0.46 per cubic meter.

A Jordanian-born chemical engineering doctoral student at University of Ottawa, Mohammed Rasool Qtaisha, invented a new desalination technology that is alleged to produce between 600% and 700% more water output per square meter of membrane than current technology. General Electric is looking into similar technology, and the U.S. National Science Foundation funded the University of Michigan to study it, as well. Patent issues and details of the technology were unresolved as of 2008.

While desalinating 1,000 US gallons (3,800 l; 830 imp gal) of water can cost as much as $3, the same amount of bottled water costs $7,945.

Environmental

Intake

In the United States, due to a recent court ruling under the Clean Water Act, ocean water intakes are no longer viable without reducing mortality of the life in the ocean, the plankton, fish eggs and fish larvae, by 90%.[32] The alternatives include beach wells to eliminate this concern, but require more energy and higher costs, while limiting output.

Outflow

All desalination processes produce large quantities of a concentrate, which may be increased in temperature, and contain residues of pretreatment and cleaning chemicals, their reaction byproducts, and heavy metals due to corrosion. Chemical pretreatment and cleaning are a necessity in most desalination plants, which typically includes the treatment against biofouling, scaling, foaming and corrosion in thermal plants, and against biofouling, suspended solids and scale deposits in membrane plants.

To limit the environmental impact of returning the brine to the ocean, it can be diluted with another stream of water entering the ocean, such as the outfall of a wastewater treatment or power plant. While seawater power plant cooling water outfalls are not as fresh as wastewater treatment plant outfalls, salinity is reduced. If the power plant is medium-to-large sized and the desalination plant is not enormous, the power plant’s cooling water flow is likely to be at least several times larger than that of the desalination plant. Another method to reduce the increase in salinity is to mix the brine via a diffuser in a mixing zone. For example, once the pipeline containing the brine reaches the sea floor, it can split into many branches, each releasing brine gradually through small holes along its length. Mixing can be combined with power plant or wastewater plant dilution.

Brine is denser than seawater due to higher solute concentration. The ocean bottom is most at risk because the brine sinks and remains there long enough to damage the ecosystem. Careful reintroduction can minimize this problem. For example, for the desalination plant and ocean outlet structures to be built in Sydney from late 2007, the water authority stated the ocean outlets would be placed in locations at the seabed that will maximize the dispersal of the concentrated seawater, such that it will be indistinguishable beyond between 50 and 75 meters (160 and 246 ft) from the outlets. Typical oceanographic conditions off the coast allow for rapid dilution of the concentrated byproduct, thereby minimizing harm to the environment.

The Kwinana Desalination Plant opened in Perth in 2007. Water there and at Queensland’s Gold Coast Desalination Plant and Sydney’s Kurnell Desalination Plant is withdrawn at only 0.1 meters per second (0.33 ft/s), which is slow enough to let fish escape. The plant provides nearly 140,000 cubic meters (4,900,000 cu ft) of clean water per day.

Alternatives without pollution

Some methods of desalination, particularly in combination with evaporation ponds and solar stills (solar desalination), do not discharge brine. They do not use chemicals in their processes nor the burning of fossil fuels. They do not work with membranes or other critical parts, such as components that include heavy metals, thus do not cause toxic waste (and high maintenance). A new approach that works like a solar still, but on the scale of industrial evaporation ponds is the Integrated Biotectural System. It can be considered “full desalination” because it converts the entire amount of saltwater intake into distilled water. One of the unique advantages of this type of solar-powered desalination is the feasibility for inland operation. Standard advantages also include no air pollution from desalination power plants and no temperature increase of endangered natural water bodies from power plant cooling-water discharge. Another important advantage is the production of sea salt for industrial and other uses. Currently, 50% of the world’s sea salt production still relies on fossil energy sources.

Alternatives to desalination

Increased water conservation and efficiency remain the most cost-effective priorities in areas of the world where there is a large potential to improve the efficiency of water use practices. Wastewater reclamation for irrigation and industrial use provides multiple benefits over desalination. Urban runoff and storm water capture also provide benefits in treating, restoring and recharging groundwater.

A proposed alternative to desalination in the American Southwest is the commercial importation of bulk water from water-rich areas either by very large crude carriers converted to water carriers, or via pipelines. The idea is politically unpopular in Canada, where governments imposed trade barriers to bulk water exports as a result of a claim filed in 1999 under Chapter 11 of the North American Free Trade Agreement (NAFTA) by Sun Belt Water Inc., a company established in 1990 in Santa Barbara, California, to address pressing local needs due to a severe drought in that area.

Experimental techniques and other developments

Many desalination techniques have been researched, with varying degrees of success.

One such process was commercialized by Modern Water PLC using forward osmosis, with a number of plants reported to be in operation.

The US government is working to develop practical solar desalination.

The Passarell process uses reduced atmospheric pressure rather than heat to drive evaporative desalination. The pure water vapor generated by distillation is then compressed and condensed using an advanced compressor. The compression process improves distillation efficiency by creating the reduced pressure in the evaporation chamber. The compressor centrifuges the pure water vapor after it is drawn through a demister (removing residual impurities) causing it to compress against tubes in the collection chamber. The compression of the vapor causes its temperature to increase. The heat generated is transferred to the input water falling in the tubes, causing the water in the tubes to vaporize. Water vapor condenses on the outside of the tubes as product water. By combining several physical processes, Passarell enables most of the system’s energy to be recycled through its subprocesses, namely evaporation, demisting, vapor compression, condensation, and water movement within the system.[44]

Geothermal energy can drive desalination. In most locations, geothermal desalination beats using scarce groundwater or surface water, environmentally and economically.[citation needed]

Nanotube membranes may prove to be effective for water filtration and desalination processes that would require substantially less energy than reverse osmosis.

Biomimetic membranes are another approach.

On June 23, 2008, Siemens Water Technologies announced technology based on applying electric fields that purports to desalinate one cubic meter of water while using only 1.5 kWh of energy. If accurate, this process would consume only one-half the energy of other processes. Currently, Oasis Water, which developed the technology, still uses three times that much energy.

Freeze-thaw desalination uses freezing to remove fresh water from frozen seawater.

In 2009, Lux Research estimated the worldwide desalinated water supply will triple between 2008 and 2020.

Desalination through evaporation and condensation for crops

The Seawater Greenhouse uses natural evaporation and condensation processes inside a greenhouse powered by solar energy to grow crops in arid coastal land.

Low-temperature thermal desalination

Originally stemming from ocean thermal energy conversion research, low-temperature thermal desalination (LTTD) takes advantage of water boiling at low pressures, potentially even at ambient temperature. The system uses vacuum pumps to create a low-pressure, low-temperature environment in which water boils at a temperature gradient of 8–10 °C (46–50 °F) between two volumes of water. Cooling ocean water is supplied from depths of up to 600 meters (2,000 ft). This cold water is pumped through coils to condense the water vapor. The resulting condensate is purified water. LTTD may also take advantage of the temperature gradient available at power plants, where large quantities of warm wastewater are discharged from the plant, reducing the energy input needed to create a temperature gradient.

Experiments were conducted in the US and Japan to test the approach. In Japan, a spray-flash evaporation system was tested by Saga University. In Hawaii, the National Energy Laboratory tested an open-cycle OTEC plant with fresh water and power production using a temperature difference of 20 C° between surface water and water at a depth of around 500 meters (1,600 ft). LTTD was studied by India’s National Institute of Ocean Technology (NIOT) from 2004. Their first LTTD plant opened in 2005 at Kavaratti in the Lakshadweep islands. The plant’s capacity is 100,000 liters (22,000 imp gal; 26,000 US gal)/day, at a capital cost of INR 50 million (€922,000). The plant uses deep water at a temperature of 7 to 15 °C (45 to 59 °F). In 2007, NIOT opened an experimental, floating LTTD plant off the coast of Chennai, with a capacity of 1,000,000 litres (220,000 imp gal; 260,000 US gal)/day. A smaller plant was established in 2009 at the North Chennai Thermal Power Station to prove the LTTD application where power plant cooling water is available.

Thermoionic process

In October 2009, Saltworks Technologies, a Canadian firm, announced a process that uses solar or other thermal heat to drive an ionic current that removes all sodium and chlorine ions from the water using ion-exchange membranes.

Shared under the Creative Commons Attribution-ShareAlike License, original text and illustrations found here: http://en.wikipedia.org/wiki/Desalination

 

Categories : Science and Industry Updates

Measuring Free Chlorine – MyronLMeters.com

Posted by 25 Nov, 2012

TweetChlorine Residuals The presence of free chlorine in drinking water indicates that: 1) a sufficient amount of chlorine was added to the water to inactivate most of the bacteria and viruses that cause diarrheal disease; and, 2) the water is protected from recontamination during transport to the home, and during storage of water in the […]

Chlorine Residuals
The presence of free chlorine in drinking water indicates that: 1) a sufficient amount of chlorine was added to the water to inactivate most of the bacteria and viruses that cause diarrheal disease; and, 2) the water is protected from recontamination during transport to the home, and during storage of water in the household. Because the presence of free residual chlorine in drinking water indicates the likely absence of disease-causing organisms, it is used as one measure of the potability of drinking water.

Adding Chlorine
When chlorine is added to water as a disinfectant, a series of reactions occurs. These reactions are graphically depicted later in this article. The first of these reactions occurs when organic materials and metals present in the water react with the chlorine and transform it into compounds that are unavailable for disinfection. The amount of chlorine used in these reactions is termed the chlorine demand of the water. Any remaining chlorine concentration after the chlorine demand is met is termed total chlorine. Total chlorine is further subdivided into: 1) the amount of chlorine that then reacts with nitrates present in the water and is transformed into compounds that are much less effective disinfectants than free chlorine (termed combined chlorine); and, 2) the free chlorine, which is the chlorine available to inactivate disease-causing organisms, and is thus a measure used to determine the potability of water.

For example, when chlorine is added to completely pure water the chlorine demand will be zero, and there will be no nitrates present, so no combined chlorine will be formed. Thus, the free chlorine concentration will be equal to the concentration of chlorine added. When chlorine is added to natural waters, especially water from surface sources such as rivers, organic material will exert a chlorine demand, and combined chlorine will be formed by reaction with nitrates. Thus, the free chlorine concentration will be less than the concentration of chlorine initially
added.

Chlorine Addition Flow Chart

Testing Free Chlorine in Drinking Water

Testing free chlorine is recommended in the following circumstances:
• To conduct dosage testing in project areas
• To monitor and evaluate projects by testing stored drinking water in households

The goal of dosage testing is to determine how much sodium hypochlorite solution to add to water that will be used for drinking to maintain free chlorine residual in the water for the average time of storage of water in the household (typically 24 hours). This goal differs from the goal of infrastructure-based (piped) water treatment systems, whose aim is effective disinfection at the endpoints (i.e., water taps) of the system. The WHO recommends “a residual concentration of free chlorine of greater than or equal to 0.5 mg/litre after at least 30 minutes contact time at pH less than 8.0.” This definition is only appropriate for users who obtain water directly from a flowing tap. A free chlorine level of 0.5 mg/L can maintain the quality of water through a distribution network, but is not optimal to maintain the quality of the water when it is stored in the home in a bucket or jerry can for 24 hours.

Recommendations:
1. At 1 hour after the addition of sodium hypochlorite solution to water there should be no more than 2.0 mg/L of free chlorine residual present (this ensures the water does not have an unpleasant taste or odor).
2. At 24 hours after the addition of sodium hypochlorite to water in containers that are used by families for water storage there should be a minimum of 0.2 mg/L of free chlorine residual present (this ensures microbiologically clean water).
This methodology is approved by the World Health Organization (WHO), and is graphically depicted below. The maximum allowable WHO value for free chlorine residual in drinking water is 5 mg/L. The minimum recommended WHO value for free chlorine residual in treated drinking water is 0.2 mg/L. CDC recommends not exceeding 2.0 mg/L due to taste concerns, and chlorine residual decays over time in stored water.

sample chlorine decay curve

1. Free Chlorine as an Indicator of Sanitizing Strength

Chlorine, which kills bacteria by way of its power as an oxidizing agent, is the most popular germicide used in water treatment. Chlorine is not only used as a primary disinfectant, but also to establish a sufficient residual level of Free Available Chlorine (FAC) for ongoing disinfection.

FAC is the chlorine that remains after a certain amount is consumed by killing bacteria or reacting with other organic (ammonia, fecal matter) or inorganic (metals, dissolved CO2, Carbonates, etc) chemicals in solution. Measuring the amount of residual free chlorine in treated water is a well accepted method for determining its effectiveness in microbial control.

The Myron L Company FCE method for measuring residual disinfecting power is based on ORP, the specific chemical attribute of chlorine (and other oxidizing germicides) that kills bacteria and microbes.

2. FCE Free Chlorine Unit

The 6PIIFCE is the first handheld device to detect free chlorine directly, by measuring ORP. The ORP value is converted to a concentration reading (ppm) using a conversion table developed by Myron L Company through a series of experiments that precisely controlled chlorine levels and excluded interferants.

Other test methods typically rely on the user visually or digitally interpreting a color change resulting from an added reagent-dye. The reagent used radically alters the sample’s pH and converts the various chlorine species present into a single, easily measured species. This ignores the effect of changing pH on free chlorine effectiveness and disregards the fact that some chlorine species are better or worse sanitizers than others.

The Myron L Company 6PIIFCE avoids these pitfalls. The chemistry of the test sample is left unchanged from the source water. It accounts for the effect of pH on chlorine effectiveness by including pH in its calculation. For these reasons, the Ultrameter II’s FCE feature provides the best reading-to-reading picture of the rise and fall in sanitizing effectivity of free available chlorine.

The 6PIIFCE also avoids a common undesirable characteristic of other ORP-based methods by including a unique Predictive ORP value in its FCE calculation. This feature, based on a proprietary model for ORP sensor behavior, calculates a final stabilized ORP value in 1 to 2 minutes rather than the 10 to 15 minutes or more that is typically required for an ORP measurement.

Categories : Application Advice, Science and Industry Updates