TweetHow many of these wastewater treatment technologies are you familiar with? What is the most effective combination of processes? How do you measure results? Who’s doing the best wastewater treatment research? Is this the best way? Or can the processes below be recombined, rethought, and retooled into something better? Activated sludge systems Advanced oxidation process [...]
How many of these wastewater treatment technologies are you familiar with? What is the most effective combination of processes?
How do you measure results? Who’s doing the best wastewater treatment research?
Is this the best way? Or can the processes below be recombined, rethought, and retooled into something better?
Activated sludge systems
Advanced oxidation process
Aerobic granular reactor
Aerobic treatment system
API oil-water separator
Bioconversion of biomass to mixed alcohol fuels
Coarse bubble diffusers
Dissolved air flotation
Expanded granular sludge bed digestion
Fine bubble diffusers
Flocculation & sedimentation
Lamella clarifier (Inclined Plate Clarifier) 
Microbial fuel cell
NERV (Natural Endogenous Respiration Vessel)
Parallel plate oil-water separator
Rotating biological contactor
Sedimentation (water treatment)
Sequencing batch reactor
Submerged aerated filter
Upflow anaerobic sludge blanket digestion
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Tweet“Thousands have lived without love, not one without water” W.H.Auden Using ultraviolet radiation to treat contaminated water started in Europe in the early 1900′s. In 1904 the first UV quartz lamp was created. Its original purpose was to treat vitamin D deficiencies but later became an integral part of most current UV water treatment systems. [...]
“Thousands have lived without love, not one without water” W.H.Auden
Using ultraviolet radiation to treat contaminated water started in Europe in the early 1900′s. In 1904 the first UV quartz lamp was created. Its original purpose was to treat vitamin D deficiencies but later became an integral part of most current UV water treatment systems. These systems did not become available until 1981 and were not widely used until 1992. The most promising use of UV treatment is in developing countries where water borne illnesses are so prevalent. Several low cost and low maintenance systems have been created and are currently being used in villages in India and Africa providing safe water to some of the poorest communities. The biggest hurdle for the widespread use of these systems is that they need a power supply to operate. Each of these systems follows the same simple design: water flows into the housing unit around the UV low pressure mercury lamps – maximum water depth is around 3 inches to insure the UV radiation can saturate the water to a high enough level that the bacteria and viruses within are neutralized. The water must be filtered before entering the UV treatment system as turbidity and dissolved solids in the water cuts down on the UV penetration into the water column.
The Science of UV treatment
How is UV radiation so effective at neutralizing bacteria and other micro-organisms? UV radiation is in the light spectrum below visible light and above x-rays. It has a wave length between 40-400nm. UVC 220-290nm is the portion of the UV spectrum used for anti bacterial purposes and has the ability to travel it the bodies of small organisms such as bacteria, viruses, yeasts and molds. The UV radiation attacks the DNA chain of these organisms causing them to loose their ability to reproduce effectively killing them. One down side to UV water treatment is that the deceased organisms will remain in the water without additional filtering to remove them.
Aftim Acra & Solar Water Disinfection
Aftim Acra is an active researcher and former professor of environmental engineering at the American University in Beirut. Acra and colleagues began research of solar water disinfection in 1979 and showed that the sun’s heat and radiation is capable of killing pathogens. The sun supplies infrared radiation, which heats the water and can kill some bacteria, as well as ultraviolet radiation, which scrambles the DNA of the bacteria to disable their reproduction functions. Depending on the temperature and clearness of the sky, solar disinfection of water in a plastic bottle can take as little as six hours of direct sunlight. SODIS (solar water disinfection) is a strategy of disinfecting water promoted by the Swiss Federal Institute of Aquatic Sciences and Technology. The SODIS organization works to give people the opportunity and means to have clean water. They work primary in South America, Asia, and Africa where there are high concentrations of people living without adequate water and water systems. The disinfection method they advocate involves filling a transparent container with contaminated water.
One problem in this method is its current reliance on plastic bottles. When the plastic these bottles are made from (Polyethylene terephthalate) react with the heat & UV radiation from the sun, chemicals in the plastic can be absorbed into the water. Another problem with the use of plastic bottles is the threads in the cap and spout of the bottle. This is one spot on the bottle that cannot be disinfected by the sun because the cap is covering it! So if the bottle is used to scoop up water from a dirty source, and then disinfected with the SODIS method, the water will only be recontaminated by the threads of the bottle once poured out. It is important to keep in mind of any possible points of recontamination (i.e. dirty hands, dirty containers).
Below is a list of some of the bacteria,viruses, molds etc. that UV treatment can remove from water and the ultraviolet dosage required to destroy greater than 99.9% of micro-organisms (measured in microwatt seconds per centimeter squared).
Bacillus megaterium (vegatative)
Bacillus subtills (vegatative)
Legionella pneumophilla (legionnaires disease)
Leptospira intrrogans (Infectious Jaundice)
Pseudomonas seruginosa (laboratory strain)
Pseudomonas aeruginosa (environmental strain)
Salmonella paratyphi (enteric fever)
Salmonella typhosa (typhoid fever)
Shigella dysenterai (dysentery)
Shigella Flexneri (dysentery)
Common yeast cake
|MOLD SPORES||microwatt sec/cm2|
|Penicillum digitatum (olive)
Penicillum expensum (olive)
PeniciHum roqueforti (green)
|Chlorella vulgaris (algae)||22000|
|Bacteriophage (E. coli)
UV Time Line
1900- UV radiation was used in some European countries to treat contaminated water.
1904- Heraeus, a medical company then, developed first UV quartz lamp in order to treat vitamin D deficiencies. That lamp developed into the tanning beds of today and into UV water treatment as well.
1976-UV water treatment was used in disinfection of aquatic systems in zoos and aquariums and in pools.It was also used in to disinfect potable and non potable water in ships.
1979- Sensors developed to monitor dose of UV to ensure a sufficient amount for disinfection. Amalgam lamps developed; which use mercury bound with bismuth and indium2, instead of just liquid mercury.
1981- Wide acceptance of UV treatment for drinking water.
1992- UV disinfection in wastewater markets open up.
1997- Aquafine Corp., a leading designer and manufacturer of high quality industrial ultraviolet water treatment systems, has nearly tripled its growth over the past four years. International business accounts for 60 percent of that growth. Aquafine now designs, manufactures and installs state-of-the-art ultraviolet water treatment systems.
2000-American Water Works Association program that investigated effectiveness of UV systems on cryptosporidium. An outbreak in Milwaukee, Wisconsin occurred in the early 1990’s Chlorination alone did not offer sufficient protection against cryptosporidium, however, UV treatment does. Sales of UV drinking water disinfection systems in the USA increased.
2001-Combination systems are being developed, a mixture of chlorination, UV, membrane filtration, reverse osmosis and ozone oxidation.
2005- The current market for UV purification systems is 30% of the total market for drinking water treatment technologies; this number is expected to rise dramatically over the next few years due to several new strict standards the U.S. Environmental Protection Agency will finalize in 2006.
2006- New EPA regulations will require drinking water to be protected against cryptosporidium and other pathogens (which chlorine can’t do effectively) and to reduce disinfection by products commonly associated with chlorine and ozone treatments.
2009- For more than 60 years, UV light has been used effectively for disinfection and purification in water treatment plants. UV light technology also is used widely in hospitals, laboratories, food and drug facilities, and in a number of consumer products.
Shared via Creative Commons Attribution ShareAlike license. Original information found here: http://www.appropedia.org/UV_water_treatment
Tweet A Book On Desalination Plant Concentrate Management by Nikolay Voutchkov, PE, BCEE of Water Globe Consulting and one of Myron L Meters valued customers This book provides an overview of the alternatives for management of concentrate generated by brackish water and seawater desalination plants, as well as site specific [...]
A Book On Desalination Plant Concentrate Management by Nikolay Voutchkov, PE, BCEE of Water Globe Consulting and one of Myron L Meters valued customers
This book provides an overview of the alternatives for management of concentrate generated by brackish water and seawater desalination plants, as well as site specific factors involved in the selection of the most viable alternative for a given project, and the environmental permitting requirements and studies associated with their implementation. The book focuses on widely used alternatives for disposal of concentrate, including discharge to surface water bodies; disposal to the wastewater collection system; deep well injection; land application; evaporation; and zero liquid discharge. Direct discharge through new outfall; discharge through existing wastewater treatment plant outfall; and co-disposal with the cooling water of existing coastal power plant are thoroughly described and design guidance for the use of these concentrate disposal alternatives is presented with engineers and practitioners in the field of desalination in mind. Key advantages, disadvantages, environmental impact issues and possible solutions are presented for each discharge alternative. Easy-to-use graphs depicting construction costs as a function of concentrate flowrate are provided for all key concentrate management alternatives.
Mr. Voutchkov is a registered professional engineer and a board certified environmental engineer (BCEE) by the American Academy of Environmental Engineers. He has over 25 years of experience in planning, environmental review, permitting and implementation of large seawater desalination, water treatment and water reclamation projects in the US and abroad. Mr. Voutchkov has extensive expertise with all phases of seawater desalination project delivery: from conceptual scoping, pilot testing and feasibility analysis; to front-end and detailed project design; environmental review and permitting; contractor procurement; project construction and operations oversight/asset management. Mr. Voutchkov is President of Water Globe Consulting a private company specialized in providing expert advisory services in the field of seawater desalination and reuse. For over 11 years prior to establishing his project advisory firm, Mr. Voutchkov was a Chief Technology Officer and Corporate Technical Director for Poseidon Resources, a private company involved in the development of the largest seawater desalination projects in the USA. In recognition of his outstanding efforts and contribution to the field of seawater desalination, Mr. Voutchkov has received a number of prestigious awards from the International Desalination Association, the International Water Association and the American Academy of Environmental Engineers. He is one of the principal authors of the American Water Works Association s Manual of Water Supply Practices on Reverse Osmosis and Nanofiltration and of the World Health Organization s Guidance for the Health and Environmental Aspects Applicable to Desalination. Mr. Voutchkov has published over 40 technical articles in the field of water and wastewater treatment and reuse, and is co-author of several books and manuals of practice on membrane treatment and desalination. He wrote a book on “Seawater Pretreatment”, which was published by Water Treatment Academy in 2010.
Desalination Plant Concentrate Management
By Nikolay Voutchkov, PE, BCEE
ISBN: 978-974-496-357-4, 181 pages, Hardcover, Published by Technobiz Communications
Ch. 1. Introduction to Concentrate Management
Ch. 2. Desalination Plant Discharge Characterization
2.1. Desalination Plant Waste Streams
2.3. Spent Pretreatment Backwash Water
2.4. Chemical Cleaning Residuals
Ch. 3. Surface Water Discharge of Concentrate
3.1. New Surface Water Discharge
3.2. Potential Environmental Impacts
3.3. Concentrate Treatment Prior to Surface Water Discharge
3.4. Design Guidelines for Surface Water Discharges
3.5. Costs for New Surface Water Discharge
3.6. Case Studies of New Surface Water Discharges
3.7. Co-Disposal with Wastewater Effluent
3.8. Co-Disposal with Power Plant Cooling Water
Ch. 4. Discharge to Sanitary Sewer
4.2. Potential Environmental Impacts
4.3. Effect on Sanitary Sewer Operations
4.4. Effect on Wastewater Treatment Operations
4.5. Effect on Water Reuse
4.6. Design and Configuration Guidelines
4.7. Costs for Sanitary Sewer Discharge
Ch. 5. Deep Well Injection
5.2. Potential Environmental Impacts
5.3. Criteria and Methods for Feasibility Assessment
5.4. Design and Configuration Guidelines
5.5. Injection Well Costs
Ch. 6. Land Application
6.2. Potential Environmental Impacts
6.3. Criteria and Methods for Feasibility Assessment
6.4. Design and Configuration Guidelines
6.5. Land Application Costs
Ch. 7. Evaporation Ponds
7.2. Potential Environmental Impacts
7.3. Criteria and Methods for Feasibility Assessment
7.4. Design and Configuration Guidelines
7.5. Evaporation Pond Costs
Ch. 8. Zero Liquid Discharge Concentrate Disposal Systems
8.2. Potential Environmental Impacts
8.3. Criteria and Methods for Feasibility Assessment
8.4. Design and Configuration Guidelines
8.5. Zero Liquid Discharge Costs
Ch. 9. Beneficial Use of Concentrate
9.1. Technology Overview
9.2. Feasibility of Beneficial Concentrate Use
Ch. 10. Regional Concentrate Management
10.1. Types of Regional Concentrate Management Systems
10.2. Use of Brackish Water Concentrate in SWRO Plants
Ch. 11. Non-Concentrate Residuals Management
11.1. Spent Pretreatment Backwash Water
11.2. Chemical Cleaning Residuals
Ch. 12. Comparison of Concentrate Management Alternatives
12.1. Selection of Concentrate Management Approach
12.3. Environmental Impacts
12.4. Regulatory Acceptance
12.5. Ease of Implementation
12.6. Site Footprint
12.7. Reliability and Operational Constraints
12.8. Energy Use
You can order your book here: http://talloaks.com/Zencart/index.php?main_page=product_info&cPath=1_9&products_id=85
TweetRedox potential has been identified by the Organisation for Economic Co-operation and Development (OECD) as one of the parameters that should be investigated for the testing of manufactured nanomaterials. There is still some ambiguity concerning this parameter, i.e., as to what and how to measure, particularly when in a nanoecotoxicological context. In this study the [...]
Redox potential has been identified by the Organisation for Economic Co-operation and Development (OECD) as one of the parameters that should be investigated for the testing of manufactured nanomaterials. There is still some ambiguity concerning this parameter, i.e., as to what and how to measure, particularly when in a nanoecotoxicological context. In this study the redox potentials of six nanomaterials (either zinc oxide (ZnO) or cerium oxide (CeO2)) dispersions were measured using an oxidation-reduction potential (ORP) electrode probe. The particles under testing differed in terms of their particle size and dispersion stability in deionised water and in various ecotox media. The ORP values of the various dispersions and how they fluctuate relative to each other are discussed. Results show that the ORP values are mainly governed by the type of liquid media employed, with little contributions from the nanoparticles. Seawater was shown to have reduced the ORP value, which was attributed to an increase in the concentration of reducing agents such as sulphites or the reduction of dissolved oxygen concentration. The lack of redox potential value contribution from the particles themselves is thought to be due to insufficient interaction of the particles at the Pt electrode of the ORP probe.
The size of engineered nanomaterials makes many novel and innovative products, as evident by the increasing number of commercially available nanotechnology products. Thus, there is a huge concern surrounding the potential toxicity of these nanomaterials and there is a need to sufficiently test such materials. The goal here is to understand and control risk, and both toxicity testing and physicochemical characterisation should be conducted. Although our current understanding of risk associated with nanomaterials is limited, attempts have been made in order to assess this systematically. Recently, Aschberger et al.  have carried out a risk assessment based on several case studies. They have indicated the risk expected from metal and metal oxide nanomaterials, which was particularly relevant in the case of algae and Daphnia. They have attributed the risk from such materials their exposure to both the particles and corresponding dissolved ions.
There is a general consensus within the nanoecotoxicological community that physicochemical characterisation of nanomaterials in complex media is not a trivial matter, and so the reliability of such measurements is vital if we are to understand and control the risk imposed by nanomaterials [2, 3]. In recent years, the OECD initiative has adopted a holistic approach to this problem and that physicochemical characterisation should be carried out with as many parameters as possible, to include redox potential. The PROSPEcT (Ecotoxicology Test Protocols for Representative Nanomaterials in Support of the OECD Sponsorship Programme) project is the UK’s contribution to this OECD initiative, and the UK is responsible for two types of nanomaterials: cerium oxide (CeO2) and zinc oxide (ZnO) . Out of all seventeen OECD parameters identified, redox potential is the most ambiguous in its definition, what this parameter means and how it is measured, in a nanoecotoxicological context.
Integral to any ecotoxicological investigation is the ability to measure the redox conditions of a given system as indicated by the redox potential. In nature, redox reactions are an important part of phenomena such as mineral weathering, bacterial respiration, and degradation of pollutants . In soil chemistry, for example, the redox potential value can estimate whether the soil is aerobic or anaerobic, and whether chemical compounds such as Fe oxides or nitrate have been chemically reduced or are present in their oxidised form. In natural waters, redox reactions include the oxidation of organic matter and various reduction reactions such as the reduction of oxygen to water, nitrate to elementary nitrogen dioxide, iron (III) to Fe (II), sulphate to sulphide, and carbon dioxide to methane . In terms of nanomaterial toxicity, redox potential is a parameter that has been associated with inducing oxidative stress. Recently, Burello and Worth , in their prediction of a given nanomaterial to induce oxidative stress, have developed a theoretical framework that combines measurements of nanoparticle particle size and redox potential. The need to accurately measure redox potential is evident, in particular we need to understand the extent that nanomaterials can influence the natural redox phenomena should these materials be released into the environment.
Redox potential is a measure of a system’s affinity for electrons, and the measurement of redox potential will only have meaning when there are reduced and oxidised species, called the redox couple, in the liquid media. The redox couple undergoes a redox reaction, in which the reduction (gain of electrons) of one redox species is accompanied by the oxidation (loss of electrons) of another . The movement of electrons, governed by kinetics (e.g., transport limitations of the redox species to the electrode), creates an electric potential. The potential measured is determined by the ratio of activities of oxidised and reduced species, as defined by the Nernst equation; this is a thermodynamic property . The redox potential can be directly measured using a potentiometer (high impedance voltmeter) with an oxidation-reduction potential (ORP) electrode . This is the recommended technique under the current OECD guidelines for the testing of nanomaterials (NMs) ; essentially it is a measurement of potential difference (in mV) across a two-electrode system, that is, an inert platinum (Pt) electrode and silver-silver chloride (Ag/AgCl) reference electrode. Rogers et al. have recently adopted this approach to measure the redox potential of nanomaterial dispersions, that is, cerium oxide dispersed in synthetic freshwater algal medium .
There are theoretical and practical difficulties associated with the measurement of redox potential and these, although not well recognised, have already been discussed for many years . Firstly, redox potential is based on the concepts of equilibrium thermodynamics, and as such it can only be adequately measured at equilibrium. A reliable redox potential measurement requires that equilibrium be established not only at the electrode, but also among the various redox couples in solution. Many redox reactions are slow and often are at nonequilibrium conditions. Secondly, most redox potential measurements represent mixed potentials, and certain redox species may not contribute significantly towards the redox potential value; that is, not all will react sufficiently fast enough at the electrode and therefore will not contribute towards stable and reliable redox potential measurements . If the particles themselves act as a redox species, then there are various factors that may prevent them contributing towards the final ORP value, including sedimentation events, diffusion limitations, and the barrier of electron exchange at the Pt electrode. If this is true, then redox potentials of nanomaterial dispersions are likely to be solely dominated by dissolved redox species in the media, rather than contributions arising from the particles themselves. In this study, we aim to investigate if this is the case. Although the ORP probe has been conveniently used in the past by scientists to directly measure redox potential, it is essential that the reliability of such data should be questioned when measuring nanomaterial dispersions. There is the risk that researchers may treat such a tool as a black box and thus may not be fully aware of the inherent limitations in the use of such a tool in these measurements.
In this study, the ORP values of six nanomaterial (either ZnO or CeO2 dispersed in one of the four liquid media) dispersions will be measured using an ORP probe. Dispersions will be carried out according to the dispersion protocol as recommended under PROSPEcT. The ORP values of the nanomaterial dispersions will be compared relative to each other and to the corresponding media blank, to identify if there is any evidence of redox contributions as a result of the particles themselves. If there are redox contributions from the particles themselves, then this is likely to happen when dispersions are stable, as this would allow sufficient time for the particles to interact with the Pt electrode. Consequently as part of the investigation, the properties associated with the different nanomaterials will be characterised, parameters of interest to include particle size, zetapotential, and dispersion stability (as reported by the so-called half life values). Zeta-potential is a well-known parameter that characterizes the electric properties of solid surface in contact with liquid and is a way to probe surface charge. The magnitude of this value is related to dispersion stability, that is, the higher the value, the better the dispersion stability . The concept of “half-life” has been put forward in the OECD guidelines as the measurand to indicate dispersion stability through time that is, the larger the half-life value; the longer it takes for the concentration to reduce by half and thus the more stable the dispersion. Lastly, the corresponding scanning electron microscopy (SEM) data, that is, the primary particle size (mean Feret diameter) and the corresponding standard deviation, will also be reported.
2. Experimental Section
All experiments were performed in a temperature-controlled laboratory, and for the redox potential measurements the temperature of the dispersions were monitored using a temperature probe (reported value of ~20°C) to ensure that any change in the readings was not attributed to temperature changes in the dispersions.
The NMs supplied from the PROSPEcT programme were of two types, either CeO2 or ZnO, and are as follows:
(a) Nanograin CeO2 (from Umicore Belgium),
(b) Nanosun ZnO (from Micronisers, Australia),
(c) Micron ZnO (from Sigma Aldrich, UK),
(d) Z-COTE ZnO (from BASF, Germany),
(e) Micron CeO2 (from Sigma Aldrich, UK),
(f) Ceria dry CeO2 (from Antaria, Australia).
The particles were used as received and did not contain any added surface stabilisers.
DI water (resistivity of 18 Mohm) from a Millipore, MilliQ system was used to prepare all aqueous solutions and suspensions.
For the purpose of zetapotential measurements, DI water with 5 mM sodium chloride (Sigma Aldrich, UK) was employed in addition to deionised water; the NaCl here served as background electrolyte for the measurement of zetapotential. The “recipes” (chemical compositions) used for making up the ecotox media were obtained from the University of Exeter, one of our collaborators in the PROSPEcT project.
Three types of ecotox relevant media were prepared accordingly and for long-term storage, the ecotox solutions were autoclaved and kept refrigerated until needed.
(a) Seawater, in which 25 g per L of Tropic Marine Sea Salt (Tropical and Marine Limited) was made up, resulting in pH ~8.8.
(b) Daphnia freshwater media. This was prepared by firstly dissolving appropriate salts (196 mg CaCl2·2H2O, 82 mg MgSO4·7H2O, 65 mg NaHCO3, 0.002 mg Na2SeO3, as obtained by appropriate dilutions of a 2 mg/mL stock solution) in 1 L of DI water. Upon continued stirring, further DI water was added so that conductivity of the solution was between ~360 and 480 μS/cm. End volume ~1–1.5 L. Final pH ~7.9.
(c) Fish freshwater media. This was prepared in three separate steps. First, salts (11.76 g CaCl2·2H2O, 4.93 g MgSO4·7H2O, 2.59 g NaHCO3, 0.23 g KCl) were dissolved separately in 1 L of DI water to make four separate stock solutions. Second, 25 mL of each salt stock solution was aliquot into a clean bottle and diluted in DI water (made up to 1 L volume). Third, 200 mL of the stock solution from step 2 was aliquoted and further diluted with DI water (made up to 1 L volume). Final pH ~7.3.
Nanomaterials were dispersed using the protocol as previously reported (Tantra, Jing, Gohil 2010) (http://www.nanotechia-prospect.org/publications/basic). Briefly, this involved weighing the nanoparticle powder into small, clean vials using an analytical mass balance. Dispersion was carried out by adding the appropriate liquid media (fish, daphnia, seawater, or DI water) dropwise (5 drops from a Pasteur pipette) and mixing using a spatula so as to produce a thick paste before adding 15 mL of liquid media and stirring gently, using the same spatula. The formation of a thick paste as a first step was necessary to allow the efficient displacement of powder-air interface with the powder-liquid interface. The subsequent deagglomeration step was carried out using an ultrasonic probe (130 Watt Ultrasonic Processors); this was done by inserting the ultrasonic probe tip (6 mm Ti) half way down the 15 mL volume of dispersed nanoparticles, and sonication was carried out with 90% amplitude for 20 s. After sonication, the nanoparticle suspension was diluted using the appropriate liquid media, in order to make up to 1 L total volume. A glass rod was used to gently mix the final dispersion, to ensure homogeneity. The dispersions (in the four different media) were stored in separate precleaned 1 L media bottles and left undisturbed. Dispersion concentrations were 50 mg/L. Analyses of redox potentials, half-lives, and zetapotentials were conducted on the day immediately after the dispersions were made.
2.2. High-Resolution SEM
SEM images were obtained using a Supra 40 field emission scanning electron microscope from Carl Zeiss (Welwyn Garden City, Hertfordshire, UK), in which the optimal spatial resolution of the microscope is a few nanometres. In-lens detector images were acquired at an accelerating voltage of 15 kV, a working distance of ≈3 mm, and a tilt angle 0°. The SEM was calibrated using a SIRA grid calibration set (SIRA, Chislehurst, Kent, UK). These are metal replicas of cross-ruled gratings of area 60 mm2 with 19.7 lines/mm for low magnification and 2160 lines/mm for high magnification calibrations, accurate to 0.2%. For analysis of the “as received” nanoparticle powders, a sample of each powder was sprinkled over a SEM carbon adhesive disc; one side of the carbon disc was placed securely on a metal stub, whilst the other side was exposed to the nanoparticle powder. Excess powder was removed by gently tapping the stub on its side until a light coating of powder on the surface became apparent. An adequate magnification was chosen for image acquisition for example, for the estimation of primary particle mean diameter, the shape and limits of the primary particles should become apparent. SEM micrographs were analysed by manually tracing contours of primary particles onto a transparency sheet. The transparency sheet was scanned for further image analysis using Image J software, which automatically calculated particle diameter dimensions.
2.3. Redox Potential Measurements
Redox potentials were measured using an ORP Oakton Waterproof ORP Testr, purchased from Cole-Parmer, UK. This, in effect, measures the potential difference across two electrodes (a Pt electrode against a double junction Ag/AgCl reference electrode). The ORP instrument manufacturer has specified a resolution of ±1 mV, with an accuracy of ±2 mV.
The electrode was used in accordance with the manufacturer’s instructions. Prior to use, the electrode was preconditioned in clean tap water for 30 minutes before a final rinse with distilled water. When making measurements, the electrode was carefully placed in a vial containing the nanomaterial dispersion sample; there must be sufficient liquid sample to cover the sensing element. The electrode was carefully stirred a little and then placed in a fixed position, slightly above the bottom of the container. The signal output was allowed to settle for 5 minutes before a reading, the “field potential,” was noted. At this point, the signal was stable and there was no further change observed within the next few minutes. After measurement, the electrode was cleaned with tap water and rinsed with distilled water, after which further measurements could be made. When not in use, the electrode was stored in Oakton electrode storage solution.
The redox potential ORP electrode was calibrated against YSI Zobell ORP Calibration Solution (purchased from Cole-Palmer). This reagent was made available in dry form and was reconstituted with 125 mL of DI water prior to use, after which the solution has ~6-month expiry date. This standard solution was used to verify the performance of the electrode at the beginning and end of the study. For Ag/AgCl reference, the redox potential value for Zobell solution was quoted to be 231 ± 10 mV (depending on temperature); at ~20°C, this value was ~237 mV.
Redox potential measurements were carried out on freshly dispersed nanomaterial in the four chosen media, as detailed above. All field potential values recorded were subjected to an additive correction factor of +206 mV. This was necessary so that the final value was reported as if the reference electrode was a standard hydrogen reference electrode (SHE) instead of the Ag/AgCl, as previously documented . The conversion from Ag/AgCl to SHE is typically on the order of 200 to 220 mV, and voltage correction is temperature dependent and also varies slightly with the concentration of KCl (~3.5 M) in the electrode filling solution.
2.4. Measurement of Half-Lives through Turbidity Measurements
Turbidity was measured using an HF Scientific-Micro100 RI turbidity meter (Cole-Palmer, UK); this meter has an infrared light source that meets the international standard ISO 7027 for turbidity measurements. The meter was calibrated on standards, which are based on AMCO-AEPA-1 microspheres; these standards are traceable to standard formazin suspension. Standard values of 1000, 10 and 0.02 NTU were used to calibrate the meter. Prior to use, the meter was allowed to warm up for 30 minutes. Sample cuvettes (HF Scientific (USA)) were used to hold the samples. Note that glass thickness may vary from cuvette to cuvette and within the same cuvette. Hence, individual vials were indexed; indexing of the cuvette entails finding the point of the cuvette that light passes through that gives the lowest reading and, once indexed, the holder can be marked accordingly. Prior to their use, cuvettes were cleaned, in accordance with manufacturer’s instructions. This involved washing the interior and exterior of the cuvette with a detergent (2% Hellmanex in DI water); it was then rinsed several times in distilled water before finally rinsing in DI water. The cuvette was further rinsed with the sample two times before filling (30 mL) and analysed. The cuvette was placed into the meter and signal allowed to settle before taking readings. Turbidity readings were taken at regular time intervals. When not in use, the vials (containing the dispersions) were stored in the dark.
2.5. Zetapotential Measurements
Electrophoretic measurements were obtained using a Zetasizer Nano ZS (Malvern Instruments, UK) equipped with a 633 nm laser. The reference standard (DTS1230, zetapotential standard from Malvern) was used to qualify the performance of the instrument. Sample preparation involved filling a disposable capillary cell (DTS1060, Malvern). Prior to their use, these cells were thoroughly cleaned with ethanol and deionised water, as recommended by the instrument vendor. For analysis, the individual cell was filled with the appropriate sample and flushed before refilling; measurement was carried out on the second filling. Malvern Instrument’s Dispersion Technology software (Version 4.0) was used for data analysis, and zetapotential values were estimated from the measured electrophoretic mobility data using the Smoluchowski equation, as documented in a previous publication .
3. Results and Discussion
Results show that ORP values are dominated by the type of liquid media used for dispersions. Nanomaterial dispersions in seawater resulted in a much smaller ORP values in comparison with dispersions made in other media. In addition, this is also the case with the ORP values of the corresponding blank media, that is, blank seawater having the smallest ORP value, of 384 mV, compared to the rest of the blank liquid media (redox potential values all above 400 mV). The ORP values reported here is not specific to a single chemical species and thus represent an aggregate oxidization-reduction of all species that can react at the Pt working electrode . The fact that the type of liquid media itself seems to have some contribution to the final ORP values is not surprising, as dissolved redox species in the liquid can easily interact with the Pt electrode of the ORP probe. In fact, such ORP measurements are often employed as an accurate gauge of water quality and for the monitoring of dissolved species in the water . Seawater in particular is shown to be more reducing in nature, that is, due to higher concentration of reducing agents (such as N O2 −) in such media, if compared to the other liquid media. The presence of reducing agent has the effect of lowering the ORP value . Furthermore, we expect a much-reduced level of oxidising agent such as dissolved oxygen in such a high saline solution, as the more saline the water can be the less oxygen the water can hold. If there is a reduction in oxidising agents, then this also has an effect of lowering the ORP value .
The ORP readings reported here were taken three times with very little variation among the replicates, that is, not more than ±2 mV. However, the second and third replicates were acquired soon after acquiring the 1st replicate, by taking the ORP probe out of the dispersion and reimmersing it back into the dispersion. The variations in the replicates here thus represent variations of the instrument’s accuracy; they will not represent any variations that might be due to other factors such as differences in dispersion quality. Table 1 also shows the change in ORP values (values reported in brackets) upon addition of the nanomaterials relative to the corresponding blank media. Results show that, in most cases, there is a change of less than ~10 mV associated upon addition of the nanomaterials. There are only three cases in which the ORP value change is greater than 15 mV: Nanograin CeO2 in fish medium, Micron CeO2 in DI water, and Ceria dry CeO2 in fish media. Currently, we offer no explanation as to why there is a much larger change in ORP values in these three cases, apart from potential variations in dispersion quality, for example, due to potential redox contaminants associated with the different samples received. In addition, no real differentiation can be made between ZnO and CeO2 particles, with Z-COTE ZnO (BASF, Germany) having the same 9 mV change as the Ceria dry CeO2 (Antaria, Australia), when both are dispersed in DI water.
Results show that zetapotential values of nanomaterials when dispersed in seawater cannot be successfully measured (due to high conductivity) and thus displayed as N/A in Table 2. Such unsuccessful measurements were reported in the corresponding “quality report” at the end of the measurement. In general, results indicate high zetapotential values for nanomaterials that are dispersed either in DI water or DI water + 5 mM NaCl. Results of the DI water are similar to the corresponding DI water + NaCl case; the addition of NaCl into the DI water was carried out so as to have greater confidence in the DI water results, as the measurement of zetapotential usually involves the presence of inert background electrolyte. Overall, results show that nanomaterials are most stable when dispersed in DI water (or DI water + NaCl) and least stable when in an ecotox media. This is true apart for the case of Micron CeO2 showing that it is least stable in DI water, that is, −7 mV when compared to other ecotox media such as fish medium, that is, −22 mV. Currently, no explanation is available for this behaviour, and dispersion stability was further measured by using the concept of half-life values (as previously discussed in the introduction, the larger the half-life, the more stable the dispersion). Results in Table 3 show that, as with zetapotential measurements, results in DI water are generally more stable (with the largest associated with Z-COTE ZnO of 4038 minutes) than when in ecotox media. However, unlike the zetapotential values, Micron CeO2 also shows the same trend, that is, most stable in DI water than when in an ecotox media. The reason for this discrepancy lies in the fact that dispersion stability was measured in two different ways: through the measurement of interparticle force (zetapotential) or through analyzing the stability via sedimentation measurements (turbidity with time). The former measurement is solely governed by the electric properties of the solid surface in contact with liquid, which will subsequently contribute towards sedimentation rate; the latter measurement is not only determined by the zetapotential value but also by other factors, for example, particle size (in which the larger particles are expected to sediment at a much faster rate) . The SEM results (Table 4) show the mean (Feret) primary particle sizes and the corresponding standard deviations (to reflect on the polydispersity of the primary particle size). Results presented in Table 4 show that the mean primary particle sizes of the samples range from ~30 nm to ~890 nm, the largest being the Micron ZnO and Micron CeO2 from Sigma Aldrich. The SD values show the large degree of polydispersity associated with samples received: high polydispersity associated with Sigma Aldrich samples, less so with Nanosun ZnO, Microniser. The SEM micrographs indicated that all particles tested here were highly aggregated together into agglomerates of irregular shape.
If there is any particle contribution towards the final ORP values, then, out of the two types of nanomaterials tested, we expected CeO2 to have a bigger contribution compared to ZnO. This is on the basis that CeO2 particle can act as a redox couple of Ce(IV)/Ce(III), which is not the case for ZnO. If CeO2 particles had contributed to the final ORP value, then we expect this to occur with Nanograin CeO2 (having the smallest particle size of ~30 nm, as shown in Table 4) and when dispersed in DI water, as this resulted in a highly stable dispersion (noted by its high dispersion stability value of 2676 min and high zeta potential value of 33 mV, as shown in Tables 3 and 2, resp.). A highly stable dispersion will mean sufficient time to allow particles to diffuse to the Pt electrode, thus interacting with the Pt electrode in order to contribute towards the final ORP reading. Hence, we expected the redox potential to be affected most by the Nanograin CeO2 in DI water and clearly this was not the case. As shown in Table 2, Nanograin CeO2 in DI water only resulted in an ORP value change of 11 mV compared to a change of 21 mV when the same particles were dispersed in fish medium. Overall, results suggest that the particles have minor effects on the final ORP readings.
The study investigated the redox potential measurements, using ORP probe electrode, of different ZnO and CeO2 dispersions, in various liquid media. The variations in the ORP readings for the different dispersions could not be regarded as being highly significant and were mainly governed by the type of liquid media that the nanomaterials were dispersed in. This is not surprising, as ORP values are dominated by the amount of dissolved chemical species in the liquid media. Dispersions in seawater resulted in the lowest ORP values, suggesting that the media is reducing in nature. This was attributed to a much higher concentration of reducing agents such as sulphites or a reduction in the concentration of dissolved oxygen under a high salinity environment. The study shows that there was little contribution from the particles themselves towards the final ORP reading, with no significant differentiation between CeO2 and ZnO. As it is clear that redox potential measurements using an ORP electrode will not indicate a particle’s contribution towards the final redox potential value, the work has highlighted the need to have better tools for such measurements. There are several alternatives to using the ORP probe, including X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) and electron energy loss spectroscopy (EELS) . However, these technologies rely on the indirect measurement of redox potential and the accuracy of the values reported may come into question.
This work was conducted as part of PROSPEcT, which is a public-private partnership between DEFRA, EPSRC, and TSB and the Nanotechnology Industries Association (NIA Ltd.) and its members, and was administered by the DEFRA LINK Programme. The authors would like to thank Dr. Alex Shard for continuing support and Mr. Jordan Tompkins for the initial handling and distribution of the nanomaterials. R. Tantra gratefully acknowledges Professor Philip N. Bartlett from the University of Southampton and Dr. Andy Wain, whose expertise in electrochemistry has immensely helped in our understanding of the study.
Copyright © 2012 Ratna Tantra 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.
Ratna Tantra, Alex Cackett, Roger Peck, Dipak Gohil, and Jacqueline Snowden, “Measurement of Redox Potential in Nanoecotoxicological Investigations,” Journal of Toxicology, vol. 2012, Article ID 270651, 7 pages, 2012. doi:10.1155/2012/270651
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TweetEnvironmental Applications Keeping the water in our lakes, rivers, and streams clean requires monitoring of water quality at many points as it gradually makes its way from its source to our oceans. Over the years ever-increasing environmental concerns and regulations have heightened the need for increased diligence and tighter restrictions on wastewater quality. Control of [...]
Keeping the water in our lakes, rivers, and streams clean requires monitoring of water quality at many points as it gradually makes its way from its source to our oceans. Over the years ever-increasing environmental concerns and regulations have heightened the need for increased diligence and tighter restrictions on wastewater quality. Control of water pollution was once concerned mainly with treating wastewater before it was discharged from a manufacturing facility into the nation’s waterways. Today, in many cases, there are restrictions on wastewater that is discharged to city sewer systems or to other publicly owned treatment facilities. Many jurisdictions even restrict or regulate the runoff of storm water — affecting not only industrial and commercial land, but also residential properties as well.
In its simplest form, water pollution management requires impoundment of storm water runoff for a specified period of time before being discharged. Normally, a few simple tests such as pH and suspended solids must be checked to verify compliance before release. If water is used in any way prior to discharge, then the monitoring requirements can expand significantly. For example, if the water is used for once-through cooling, testing may include temperature, pH, total dissolved solids (TDS), chemical oxygen demand (COD), and biochemical oxygen demand (BOD), to name a few.
Once water is used in a process, some form of treatment is often required before it can be discharged to a public waterway. If wastewater is discharged to a city sewer or publicly owned facility, and treatment is required, the quality is often measured and the cost is based not only on the quantity discharged, but also the amount of treatment required. As a minimum requirement suspended solids must be removed. Filtering or using clarifiers often accomplishes such removal. Monitoring consists of measuring total suspended solids (TSS) or turbidity.
If inorganic materials have been introduced into the water, their concentration must be reduced to an acceptable level. Inorganics, such as heavy metals, typically are removed by raising the pH to form insoluble metal oxides or metal hydroxides. The precipitated contaminants are filtered or settled out. Afterward, the pH must be adjusted back into a “normal” range, which often requires continuous monitoring of pH.
Organic materials by far require the most extensive treatment. Many different methods have been devised to convert soluble organic compounds into insoluble inorganic matter. Most of these involve some form of biological oxidation treatment. Bacteria are used to metabolize the organic materials into carbon dioxide and solids, which can be easily removed. To insure that these processes work smoothly and efficiently requires regular monitoring of the health of the biological organisms. The level of food (organic material), nutrients (nitrogen and phosphorous), dissolved oxygen, and pH are some of the parameters that must be controlled. After bio-oxidation the wastewater is filtered or clarified. Often the final effluent is treated with an oxidizing compound such as chlorine to kill any remaining bacterial agents, but any excess oxidant normally must be removed prior to discharge. Oxidation Reduction Potential (ORP)/Redox is ideal for monitoring the level of oxidants before and after removal. The final effluent stream must be monitored to make sure it meets all regulatory requirements.
The monitoring of wastewater pollution does not end there. Scientists are continuously testing water in streams, ground water, lakes, lagoons, and other bodies of water to determine if and what effects any remaining contamination is having on the receiving waters and its associated aquatic life. Measurements may include pH, conductivity, TDS, temperature, dissolved oxygen, TSS and organic levels (COD and BOD).
Environmental testing is not limited to monitoring of wastewater systems. Control of air emissions often includes gas-cleaning systems that involve the use of water. Wet scrubbers and wet electrostatic precipitators are included in this group. A flue gas desulfurization (FGD) system is one type of wet scrubber that uses slurry of lime, limestone, or other caustic material to react with sulfur compounds in the flue gas. The key to reliable operation of these units is proper monitoring of solids levels and pH. After use, the water in these systems must be treated or added to other wastewater from the plant, where it is treated by one of the methods previously discussed.
With proper monitoring, systems that maintain cleaner air and water can be operated efficiently and effectively. Such operation will go a long way toward maintaining a cleaner environment for future generations.
Myron L Meters offers a full line of handheld instruments and in-line monitor/controllers that can be used to measure or monitor many of the parameters previously mentioned. The following table lists some of the model numbers for measuring, monitoring, or controlling pH, conductivity, TDS and ORP. For additional information, please refer to our data sheets or Ask An Expert at MyronLMeters.com.
Note: When using a monitor/controller to measure pH in streams that contain heavy metals, sulfides, or other materials that react with silver, Myron L Meters recommends using a double junction pH sensor with a potassium nitrate (KNO3) reference gel to avoid fouling the silver electrode. See our 720II Sensor Selection Guide for pH and ORP Monitor/controllers for more information.
Ultrameter II 6P
Multi-Parameter: Conductivity, TDS, Resistivity, pH, ORP, Temperature, Free Chlorine (FCE)
+/-1% Accuracy of Reading
Memory Storage: Save up to 100 samples w/ Date & Time stamp
Wireless Download Module Optional
TweetA TDS Meter indicates the Total Dissolved Solids (TDS) of a solution (the concentration of dissolved solids in it). Since dissolved ionized solids such as salts and minerals increase the conductivity of a solution, a TDS meter measures the conductivity of the solution and estimates the TDS from that. Dissolved organic solids such as sugar [...]
A TDS Meter indicates the Total Dissolved Solids (TDS) of a solution (the concentration of dissolved solids in it). Since dissolved ionized solids such as salts and minerals increase the conductivity of a solution, a TDS meter measures the conductivity of the solution and estimates the TDS from that.
Dissolved organic solids such as sugar and colloids don’t affect the conductivity of a solution much so a TDS meter does not include them in its reading.
Units of TDS
A TDS meter usually displays TDS in parts per million (ppm). For example, a TDS reading of 1 ppm would indicate there is 1 milligram of dissolved solids in each kilogram of water.
The two chief methods of measuring total dissolved solids are gravimetry and conductivity. Gravimetric methods are the most accurate and involve evaporating the liquid solvent and measuring the mass of residues left. This method is generally the best but time-consuming. If inorganic salts comprise the majority of TDS, gravimetric methods are recommended.
Electrical conductivity of water is directly related to the concentration of dissolved ionized solids in the water. Ions from the dissolved solids in water create the water’s ability to conduct an electrical current, which can be measured using a conventional conductivity meter or TDS meter. When correlated with laboratory TDS measurements, conductivity provides an approximate value for the TDS concentration.
Total Dissolved Solids (TDS) is a measure of the combined content of all inorganic and organic substances contained in a liquid in: molecular, ionized or micro-granular (colloidal sol) suspended form. The operational definition is that the solids must be small enough to survive filtration through a two micrometer sieve. Total dissolved solids are normally discussed only for freshwater systems, as salinity comprises some of the ions constituting the definition of TDS. The principal application of TDS is in the study of water quality for streams, rivers and lakes, although TDS is not generally considered a primary pollutant (e.g. it is not deemed to be associated with health effects) it is used as an indication of aesthetic characteristics of drinking water and as an aggregate indicator of the presence of a broad array of chemical contaminants.
Primary sources for TDS in receiving waters are agricultural and residential runoff, leaching of soil contamination and point source water pollution discharge from industrial or sewage treatment plants. The most common chemical constituents are calcium, phosphates, nitrates, sodium, potassium and chloride, which are found in nutrient runoff, storm water runoff and runoff from snowy climates where road de-icing salts are applied. The chemicals may be cations, anions, molecules or agglomerations on the order of one thousand or fewer molecules, so long as a soluble micro-granule is formed. More exotic and harmful elements of TDS are pesticides arising from surface runoff. Certain naturally occurring total dissolved solids arise from the weathering and dissolution of rocks and soils. The United States has established a secondary water quality standard of 500 mg/l to provide for palatability of drinking water.
TDS Measurement Applications
High TDS levels indicate hard water, which can cause scale buildup in pipes, valves, and filters, reducing performance and adding to system maintenance costs. These effects can be seen in aquariums, spas, swimming pools, and reverse osmosis water treatment systems. Typically, in these applications, total dissolved solids are tested frequently, and filtration membranes are checked in order to prevent adverse effects.
In the case of hydroponics and aquaculture, TDS is often monitored in order to create a water quality environment favorable for organism productivity. For freshwater oysters, trouts, and other high value seafood, highest productivity and economic returns are achieved by mimicking the TDS and pH levels of each species’ native environment. For hydroponic uses, TDS is considered one of the best indices of nutrient availability for the aquatic plants being grown.
Because the threshold of acceptable aesthetic criteria for human drinking water is 500 mg/l, there is no general concern for odor, taste, and color at a level much lower than is required for harm. A number of studies have been conducted and indicate various species’ reactions range from intolerance to outright toxicity due to elevated TDS. The numerical results must be interpreted cautiously, as true toxicity outcomes will relate to specific chemical constituents. Nevertheless, some numerical information is a useful guide to the nature of risks in exposing aquatic organisms or terrestrial animals to high TDS levels. Most aquatic ecosystems involving mixed fish fauna can tolerate TDS levels of 1000 mg/l.
Boilers & cooling towers, Deionization, Reverse osmosis, Chemical concentrations, Printing fountain solutions, Swimming pools & spas, Water pollution control, Wastewater & more…
Myron L Meters Top-selling TDS Meters
ULTRAPEN PT1 Conductivity – TDS – Salinity Pen
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EP-10: 0-10, 100, 1000, 10,000 micromhos/microsiemens
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Multi-Parameter: Conductivity, TDS, Resistivity, Temperature
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TweetWhat is pH and why do I need to measure it? pH measures the amount of acidity or alkalinity in a food or solution using a numerical scale between 1 and 14. A pH value of 1 is most acidic, a pH value of 7 is neutral, and values above 7 are referred to as [...]
What is pH and why do I need to measure it?
pH measures the amount of acidity or alkalinity in a food or solution using a numerical scale between 1 and 14. A pH value of 1 is most acidic, a pH value of 7 is neutral, and values above 7 are referred to as basic or alkaline. Acidified foods have a pH value less than or equal to 4.6. The proper pH of a canned food product can be critical to ensuring the safety of the product. It is very important that pH testing be done correctly and accurately.
How is pH measured?
If you process acidified foods, you will be required to monitor the pH of the product that you produce. Depending on the pH of the product, you may be able to use paper pH strips (often referred to as litmus paper), or required to use a pH meter. Paper strips that measure pH rely on a color change in the paper to indicate product pH. Paper strips can be used to measure pH if the product pH is less than 4.0. Paper strips are an inexpensive way to test pH, but can be inaccurate or difficult to read. A pH meter measures the amount of hydrogen-ion (acid) in solution using a glass electrode immersed in the solution. A pH meter must be used when product pH is greater than, or equal to, 4.0. If you are canning acidified foods, accurately monitoring and recording the product pH is key to knowing that you are selling a safe product.
What is equilibrium pH?
Equilibrium pH is the pH of a food product after the added acid has reached throughout the food; the pH of the acid brine and the food that have equilibrated. When you monitor pH as part of process monitoring, it is the equilibrium pH that you are measuring. For a proper pH reading, you should test the pH of the product roughly 24 hours after processing, once the jars have cooled to room temperature and stabilized. Do not take the pH of a product just before or right after canning because it will not be an accurate measure of the equilibrium pH.
What should I look for if I need to purchase a pH meter?
If you are required to check your product pH with a meter, there are several things to consider.
Accuracy. Accuracy is listed as a range of +0.XX pH units. This means that the meter may read so many pH units above or below the actual pH of the product. Purchase a pH meter with an accuracy of +0.02 units or better. For instance, a pH meter with an accuracy of
+0.01 is a good choice. A pH meter with an accuracy of +0.10 is not a good choice, it is not accurate enough for all products.
All pH meters must be calibrated (checked against a known standard) to assure accuracy. Standards are colored liquids of known pH. Buy a meter that uses at least a 2-point calibration; for acidified foods you will calibrate your meter with pH 4.0 and 7.0 buffers.
Electrode. The electrode is the part of the instrument that is immersed in solution. When considering which pH meter to purchase, consider the cost of replacement electrodes. Some electrodes have special non-clog tips and these may be useful is you will be measuring the pH of foods that are not easily blended.
Temperature. pH readings are affected by temperature. In order to get an accurate reading, the pH meter must be calibrated at the same temperature as the samples being tested. More expensive meters will compensate for variations in sample temperature (too warm or too cold). Myron L meters have automatic temperature compensation. If you can afford a meter with this feature, it’s nice to have.
What should I buy?
The cost of a pH meter ranges from under $100 to well over $500. As a starting point, there are several styles that small food and beverage processors currently use.
Testing the Equilibrium pH of an Acidified Food Product
1. Open one jar and take a representative sample of your food product once it has cooled, usually 12 to 24 hours after processing. You should sample each batch. Heating will drive the acid into your food product; sampling after processing (and cooling) will give you an accurate reading of the equilibrium pH.
2. Strain the solids, draining out the liquid (brine) from the jar. Place the strained solids into a blender.
3. Blend the product, adding distilled water if necessary, to produce a slurry. Added distilled water will not change the pH of the product and will allow for effective blending. You can purchase distilled water at many grocery stores or drug stores.
4. Use a calibrated pH meter to measure pH.
The pH meter must be calibrated using at least 2-point calibration with pH 4.0 and 7.0 buffers. Myron L Meters recommends a three point calibration.
The pH meter must be calibrated each day that you use it. A pH meter must be used to monitor the pH of foods with an equilibrium pH greater than 4.0.
5. Record the results in your batch log.
*Myron L meters are used by Tyson, Sara Lee, Gordon Food Service, Better Baked Foods, Schreiber Foods, Homestead Slow Foods, and others in the food
These are our two most popular handheld pH meters:
ULTRAPEN PT2 pH and Temperature Pen
Accuracy of +/- 0.01 pH
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Ultrameter II – 6PII
Multi-Parameter: Conductivity, TDS, Resistivity, pH, ORP, Temperature, Free Chlorine (FCE)
+/-1% Accuracy of Reading
Memory Storage: Save up to 100 samples w/ Date & Time stamp
Wireless Download Module Optional
TweetReverse Osmosis and RO Meters – MyronLMeters.com Schematics of a reverse osmosis system (desalination) using a pressure exchanger. 1: Sea water inflow, 2: Fresh water flow (40%), 3: Concentrate flow (60%), 4: Sea water flow (60%), 5: Concentrate (drain), A: Pump flow (40%), B: Circulation pump, C: Osmosis unit [...]
Reverse Osmosis and RO Meters – MyronLMeters.com
Schematics of a reverse osmosis system (desalination) using a pressure exchanger.
1: Sea water inflow,
2: Fresh water flow (40%),
3: Concentrate flow (60%),
4: Sea water flow (60%),
5: Concentrate (drain),
A: Pump flow (40%),
B: Circulation pump,
C: Osmosis unit with membrane,
D: Pressure exchanger
Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be “selective,” this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.
In normal osmosis, the solvent naturally moves from an area of low solute concentration (High Water Potential), through a membrane to an area of high solute concentration (Low Water Potential). The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, there are key differences between reverse osmosis and filtration. The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Reverse osmosis, however, involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure, and water flux rate. Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other substances from the water molecules.
Reverse osmosis is the process of forcing a solvent from a region of high solute concentration through a semipermeable membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. The largest and most important application of reverse osmosis is to the separation of pure water from seawater and brackish waters; seawater or brackish water is pressurized against one surface of the membrane, causing transport of salt-depleted water across the membrane and emergence of potable drinking water from the low-pressure side.
The membranes used for reverse osmosis have a dense layer in the polymer matrix — either the skin of an asymmetric membrane or an interfacially polymerized layer within a thin-film-composite membrane — where the separation occurs. In most cases, the membrane is designed to allow only water to pass through this dense layer, while preventing the passage of solutes (such as salt ions). This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh and brackish water, and 40–82 bar (600–1200 psi) for seawater, which has around 27 bar (390 psi) natural osmotic pressure that must be overcome. This process is best known for its use in desalination (removing the salt and other minerals from sea water to get fresh water), but since the early 1970s it has also been used to purify fresh water for medical, industrial, and domestic applications.
Osmosis describes how solvent moves between two solutions separated by a permeable membrane to reduce concentration differences between the solutions. When two solutions with different concentrations of a solute are mixed, the total amount of solutes in the two solutions will be equally distributed in the total amount of solvent from the two solutions. Instead of mixing the two solutions together, they can be put in two compartments where they are separated from each other by a semipermeable membrane. The semipermeable membrane does not allow the solutes to move from one compartment to the other, but allows the solvent to move. Since equilibrium cannot be achieved by the movement of solutes from the compartment with high solute concentration to the one with low solute concentration, it is instead achieved by the movement of the solvent from areas of low solute concentration to areas of high solute concentration. When the solvent moves away from low concentration areas, it causes these areas to become more concentrated. On the other side, when the solvent moves into areas of high concentration, solute concentration will decrease. This process is termed osmosis. The tendency for solvent to flow through the membrane can be expressed as “osmotic pressure”, since it is analogous to flow caused by a pressure differential. Osmosis is an example of diffusion.
In reverse osmosis, in a similar setup as that in osmosis, pressure is applied to the compartment with high concentration. In this case, there are two forces influencing the movement of water: the pressure caused by the difference in solute concentration between the two compartments (the osmotic pressure) and the externally applied pressure.
Around the world, household drinking water purification systems, including a reverse osmosis step, are commonly used for improving water for drinking and cooking.
Such systems typically include a number of steps:
a sediment filter to trap particles, including rust and calcium carbonate
optionally, a second sediment filter with smaller pores
an activated carbon filter to trap organic chemicals and chlorine, which will attack and degrade TFC reverse osmosis membranes
a reverse osmosis (RO) filter, which is a thin film composite membrane (TFM or TFC)
optionally, a second carbon filter to capture those chemicals not removed by the RO membrane
optionally an ultra-violet lamp for sterilizing any microbes that may escape filtering by the reverse osmosis membrane
In some systems, the carbon prefilter is omitted, and cellulose triacetate membrane (CTA) is used. The CTA membrane is prone to rotting unless protected by chlorinated water, while the TFC membrane is prone to breaking down under the influence of chlorine. In CTA systems, a carbon postfilter is needed to remove chlorine from the final product, water.
Portable reverse osmosis (RO) water processors are sold for personal water purification. To work effectively, the water feeding to these units should be under some pressure (40 psi or greater is the norm). Portable RO water processors can be used by people who live in rural areas without clean water, far away from the city’s water pipes. Rural people filter river or ocean water themselves, as the device is easy to use (saline water may need special membranes). Some travelers on long boating, fishing, or island camping trips, or in countries where the local water supply is polluted or substandard, use RO water processors coupled with one or more UV sterilizers. RO systems are also now extensively used by marine aquarium enthusiasts. In the production of bottled mineral water, the water passes through an RO water processor to remove pollutants and microorganisms. In European countries, though, such processing of Natural Mineral Water (as defined by a European Directive) is not allowed under European law. In practice, a fraction of the living bacteria can and do pass through RO membranes through minor imperfections, or bypass the membrane entirely through tiny leaks in surrounding seals. Thus, complete RO systems may include additional water treatment stages that use ultraviolet light or ozone to prevent microbiological contamination.
Membrane pore sizes can vary from 0.1 nanometres (3.9×10−9 in) to 5,000 nanometres (0.00020 in) depending on filter type. “Particle filtration” removes particles of 1 micrometre (3.9×10−5 in) or larger. Microfiltration removes particles of 50 nm or larger. “Ultrafiltration” removes particles of roughly 3 nm or larger. “Nanofiltration” removes particles of 1 nm or larger. Reverse osmosis is in the final category of membrane filtration, “hyperfiltration”, and removes particles larger than 0.1 nm.
Water and waste water purification
Rain water collected from storm drains is purified with reverse osmosis water processors and used for landscape irrigation and industrial cooling in Los Angeles and other cities, as a solution to the problem of water shortages.
In industry, reverse osmosis removes minerals from boiler water at power plants. The water is boiled and condensed repeatedly. It must be as pure as possible so that it does not leave deposits on the machinery or cause corrosion. The deposits inside or outside the boiler tubes may result in under-performance of the boiler, bringing down its efficiency and resulting in poor steam production, hence poor power production at turbine.
It is also used to clean effluent and brackish groundwater. The effluent in larger volumes (more than 500 cu. meter per day) should be treated in an effluent treatment plant first, and then the clear effluent is subjected to reverse osmosis system. Treatment cost is reduced significantly and membrane life of the RO system is increased.
The process of reverse osmosis can be used for the production of deionized water.
RO process for water purification does not require thermal energy. Flow through RO system can be regulated by high pressure pump. The recovery of purified water depends upon various factors including membrane sizes, membrane pore size, temperature, operating pressure and membrane surface area.
In 2002, Singapore announced that a process named NEWater would be a significant part of its future water plans. It involves using reverse osmosis to treat domestic wastewater before discharging the NEWater back into the reservoirs.
In addition to desalination, reverse osmosis is a more economical operation for concentrating food liquids (such as fruit juices) than conventional heat-treatment processes. Research has been done on concentration of orange juice and tomato juice. Its advantages include a lower operating cost and the ability to avoid heat-treatment processes, which makes it suitable for heat-sensitive substances like the protein and enzymes found in most food products.
Reverse osmosis is extensively used in the dairy industry for the production of whey protein powders and for the concentration of milk to reduce shipping costs. In whey applications, the whey (liquid remaining after cheese manufacture) is concentrated with RO from 6% total solids to 10–20% total solids before UF (ultrafiltration) processing. The UF retentate can then be used to make various whey powders, including whey protein isolate used in bodybuilding formulations. Additionally, the UF permeate, which contains lactose, is concentrated by RO from 5% total solids to 18–22% total solids to reduce crystallization and drying costs of the lactose powder.
Although use of the process was once avoided in the wine industry, it is now widely understood and used. An estimated 60 reverse osmosis machines were in use in Bordeaux, France in 2002. Known users include many of the elite classed growths.
Because of its lower mineral content, reverse osmosis water is often used in car washes during the final vehicle rinse to prevent water spotting on the vehicle. Reverse osmosis is often used to conserve and recycle water within the wash/pre-rinse cycles, especially in drought stricken areas where water conservation is important. Reverse osmosis water also enables the car wash operator to reduce the demands on the vehicle drying equipment, such as air blowers.
Maple syrup production
In 1946, some maple syrup producers started using reverse osmosis to remove water from sap before the sap is boiled down to syrup. The use of reverse osmosis allows approximately 75-90% of the water to be removed from the sap, reducing energy consumption and exposure of the syrup to high temperatures. Microbial contamination and degradation of the membranes has to be monitored.
For small-scale production of hydrogen, reverse osmosis is sometimes used to prevent formation of minerals on the surface of electrodes.
Many reef aquarium keepers use reverse osmosis systems for their artificial mixture of seawater. Ordinary tap water can often contain excessive chlorine, chloramines, copper, nitrogen, phosphates, silicates, or many other chemicals detrimental to the sensitive organisms in a reef environment. Contaminants such as nitrogen compounds and phosphates can lead to excessive, and unwanted, algae growth. An effective combination of both reverse osmosis and deionization (RO/DI) is the most popular among reef aquarium keepers, and is preferred above other water purification processes due to the low cost of ownership and minimal operating costs. Where chlorine and chloramines are found in the water, carbon filtration is needed before the membrane, as the common residential membrane used by reef keepers does not cope with these compounds.
Areas that have either no or limited surface water or groundwater may choose to desalinate seawater or brackish water to obtain drinking water. Reverse osmosis is a common method of desalination, although 85 percent of desalinated water is produced in multistage flash plants.
Large reverse osmosis and multistage flash desalination plants are used in the Middle East, especially Saudi Arabia. The energy requirements of the plants are large, but electricity can be produced relatively cheaply with the abundant oil reserves in the region. The desalination plants are often located adjacent to the power plants, which reduces energy losses in transmission and allows waste heat to be used in the desalination process of multistage flash plants, reducing the amount of energy needed to desalinate the water and providing cooling for the power plant.
Sea water reverse osmosis (SWRO) is a reverse osmosis desalination membrane process that has been commercially used since the early 1970s. Its first practical use was demonstrated by Sidney Loeb and Srinivasa Sourirajan from UCLA in Coalinga, California. Because no heating or phase changes are needed, energy requirements are low in comparison to other processes of desalination, but are still much higher than those required for other forms of water supply (including reverse osmosis treatment of wastewater).
The Ashkelon seawater reverse osmosis (SWRO) desalination plant in Israel is the largest in the world. The project was developed as a BOT (Build-Operate-Transfer) by a consortium of three international companies: Veolia water, IDE Technologies and Elran.
The typical single-pass SWRO system consists of the following components:
High pressure pump
Remineralization and pH adjustment
Pretreatment is important when working with RO and nanofiltration (NF) membranes due to the nature of their spiral wound design. The material is engineered in such a fashion as to allow only one-way flow through the system. As such, the spiral wound design does not allow for backpulsing with water or air agitation to scour its surface and remove solids. Since accumulated material cannot be removed from the membrane surface systems, they are highly susceptible to fouling (loss of production capacity). Therefore, pretreatment is a necessity for any RO or NF system. Pretreatment in SWRO systems has four major components:
Screening of solids: Solids within the water must be removed and the water treated to prevent fouling of the membranes by fine particle or biological growth, and reduce the risk of damage to high-pressure pump components.
Cartridge filtration: Generally, string-wound polypropylene filters are used to remove particles of 1–5 µm diameter.
Dosing: Oxidizing biocides, such as chlorine, are added to kill bacteria, followed by bisulfite dosing to deactivate the chlorine, which can destroy a thin-film composite membrane. There are also biofouling inhibitors, which do not kill bacteria, but simply prevent them from growing slime on the membrane surface and plant walls.
Prefiltration pH adjustment: If the pH, hardness and the alkalinity in the feedwater result in a scaling tendency when they are concentrated in the reject stream, acid is dosed to maintain carbonates in their soluble carbonic acid form.
CO32– + H3O+ = HCO3– + H2O
HCO3– + H3O+ = H2CO3 + H2O
Carbonic acid cannot combine with calcium to form calcium carbonate scale. Calcium carbonate scaling tendency is estimated using the Langelier saturation index (LSI). Adding too much sulfuric acid to control carbonate scales may result in calcium sulfate, barium sulfate or strontium sulfate scale formation on the RO membrane.
Antiscalants: Scale inhibitors (also known as antiscalants) prevent formation of all scales compared to acid, which can only prevent formation of calcium carbonate and calcium phosphate scales. In addition to inhibiting carbonate and phosphate scales, antiscalants inhibit sulfate and fluoride scales, disperse colloids and metal oxides. Despite claims that antiscalants can inhibit silica formation, there is no concrete evidence to prove that silica polymerization can be inhibited by antiscalants. Antiscalants can control acid soluble scales at a fraction of the dosage required to control the same scale using sulfuric acid.
Some small scale desalination units use Beach wells, they are usually drilled on the seashore in close vicinity to the ocean. These intake facilities are relatively simple to build and the seawater they collect is pretreated via slow filtration through the subsurface sand/seabed formations in the area of source water extraction. Raw seawater collected using beach wells is often of better quality in terms of solids, silt, oil and grease, natural organic contamination and aquatic microorganisms, compared to open seawater intakes. Sometimes, beach intakes may also yield source water of lower salinity.
High pressure pump
The pump supplies the pressure needed to push water through the membrane, even as the membrane rejects the passage of salt through it. Typical pressures for brackish water range from 225 to 375 psi (15.5 to 26 bar, or 1.6 to 2.6 MPa). In the case of seawater, they range from 800 to 1,180 psi (55 to 81.5 bar or 6 to 8 MPa). This requires a large amount of energy.
The layers of a membrane
The membrane assembly consists of a pressure vessel with a membrane that allows feed water to be pressed against it. The membrane must be strong enough to withstand whatever pressure is applied against it. RO membranes are made in a variety of configurations, with the two most common configurations being spiral-wound and hollow-fiber.
Remineralization and pH adjustment
The desalinated water is very corrosive and is “stabilized” to protect downstream pipelines and storages, usually by adding lime or caustic to prevent corrosion of concrete lined surfaces. Liming material is used to adjust pH between 6.8 and 8.1 to meet the potable water specifications, primarily for effective disinfection and for corrosion control.
Post-treatment consists of preparing the water for distribution after filtration. Reverse osmosis is an effective barrier to pathogens, however post-treatment provides secondary protection against compromised membranes and downstream problems. Disinfection by means of UV lamps (sometimes called germicidal or bactericidal) may be used to sterilize pathogens which bypassed the reverse osmosis process. Chlorination or chloramination (chlorine and ammonia) protects against pathogens which may have lodged in the distribution system downstream, such as from new construction, backwash, compromised pipes, etc.
Household reverse osmosis units use a lot of water because they have low back pressure. As a result, they recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water. Because waste water carries with it the rejected contaminants, methods to recover this water are not practical for household systems. Waste water is typically connected to the house drains and will add to the load on household septic systems. An RO unit delivering 5 gallons of treated water a day may discharge anywhere between 20 and 90 gallons of waste water a day. For household use, however, and based on consumption of half a gallon per day, this may amount to less than a toilet-flush per day.
Large-scale industrial/municipal systems have a production efficiency of 75% – 80%, or as high as 90%, because they can generate the high pressure needed for more efficient RO filtration. On the other hand, as efficiency of waste water rates increases in commercial operations effective removal rates tend to become reduced, as evidenced by TDS counts.
Reverse Osmosis Removes Minerals
Reverse Osmosis (RO) removesd more than 90-99.99% of all the contaminants including minerals from the drinking water supply. RO removes minerals because they have larger molecules than water. The subject of minerals and RO created controversy and disagreement among water and health professionals. The World Health Organization (WHO) stated that most of healthy minerals needed by the human body come from food or dietary supplementary sources and not from drinking tap water. In addition, some minerals found in water can be harmful to human health. The evidence is strong that calcium and magnesium are essential elements for human body. However, this is not to suggest that we should make up this deficiency through water consumption. Tap water presents a variety of inorganic minerals which human body has difficulty absorbing. Their presence is suspect in a wide array of degenerative diseases, such as hardening of the arteries, arthritis, kidney stones, gall stones, glaucoma, cataracts, hearing loss, emphysema, diabetes, and obesity. What minerals are available, especially in “hard” tap water, are poorly absorbed, or rejected by cellular tissue sites, and, if not evacuated, their presence may cause arterial obstruction, and internal damage (Dennison, 193; Muehling, 1994; Banik, 1989).
A number of studies have looked at the long term health effects of drinking demineralized water. However, demineralized water can be remineralized, and this process has been done in instances when processing demineralized water for consumption. Dasani water uses this process.
Water filtered or treated by RO is generally pure, clean, and healthy. RO treatment is currently the only technology that can remove emerging contaminants (prescription drugs and perchlorate) and some others (i.e., arsenic, cyanide, and fluoride) that are difficult to remove by other methods. Consumers should not be concerned about the removal of minerals by RO system. WHO (2009) and WQA (2011) pointed out, that the human body obtains most minerals from food or supplements, not from drinking water.
Popular RO Meters
RO Meter – RO-1: 0-1250 ppm with color band
Instant and accurate TDS tests
Electronic Internal Standard for easy field calibration
Fast Auto Temperature Compensation
Rugged design for years of trouble-free testing
Simple to use
758II: Conductivity Digital Monitor/Controller
The choice of professionals for years, this compact instrument has been designed specifically to demonstrate and test Point of Use (POU) reverse osmosis or distillation systems. By measuring electrical conductivity, it will quickly determine the parts per million/Total Dissolved Solids (ppm/TDS) of any drinking water.
With a single ‘before and after’ test, this handy device effectively demonstrates how your RO or distillation system eliminates harmful dissolved solids. It will also service test systems, including membrane evaluation programs.
The unique circuitry of the 750 Series II Conductivity Monitor/controllers guarantees accurate and reliable measurements. Drift-free performance is assured by “field proven” electronics, including automatic DC offset compensation and highly accurate drive voltage.
Since temperature compensation is at the heart of accurate water measurement, all Myron L Monitor/controllers feature a highly refined and precise TC circuit. This feature perfectly matches the water temperature coefficient as it changes. All models corrected to 25′C. The TC may be disabled to conform with USP requirements.
Built-in electronic calibration allows for fast quality checks without standard solutions. (Note: for maximum system accuracy standard solutions are recommended).
For use with any two-bank supply systems (DI banks, RO systems, etc)
Must use with Inline Monitor/Controller
The AQUASWITCH I is a special purpose dedicated instrument which automatically “switches” from an exhausted DI or RO bank to a fresh stand-by bank. LEDs continually give the condition of both banks. An alarm output is activated as each bank is depleted.
Ultrameter III – 9PTK
LSI Calculator for hypothetical water balance calculations
Wireless data transfer capability with bluDock option
Auto-ranging delivers increased resolution across diverse applications
Adjustable Temperature Compensation and Cond/TDS conversion ratios for user-defined solutions
Nonvolatile memory of up to 100 readings for stored data protection
Date & time stamp makes record-keeping easy
pH calibration prompts alert you when maintenance is required
Auto-off minimizes energy consumption
Low battery indicator
(Includes instrument with case and solutions)