Archive for January, 2013

Application Bulletin: POOL & SPA Water – MyronLMeters.com

Posted by 31 Jan, 2013

Tweet                 Anyone responsible for operating and maintaining a swimming pool or spa has to test, monitor, and control complex, interdependent chemical factors that affect the quality of water. Additionally, aquatic facilities operators must be familiar with all laws, regulations, and guidelines governing what these parameters should be. […]

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Anyone responsible for operating and maintaining a swimming pool or spa has to test, monitor, and control complex, interdependent chemical factors that affect the quality of water. Additionally, aquatic facilities operators must be familiar with all laws, regulations, and guidelines governing what these parameters should be.

Why? Because the worst breeding ground for any kind of microorganism is a warm (enough) stagnant pool of water. People plus stagnant water equals morbid illness. That’s why pools have to be circulated, filtered, and sanitized –  with any number of chemicals or methods, but most frequently with chlorine compounds. However, adding chemicals that kill the bad microorganisms can also make the water uncomfortable, and in some cases unsafe, for swimmers. Additionally, if all the chemical factors of the water are not controlled, the very structures and equipment that hold the water and keep it clean are ruined.

So the pool professional must perform a delicate balancing act with all the factors that affect both the health and comfort of bathers and the equipment and structures that support this. Both water balance – or mineral saturation control – and sanitizer levels must constantly be maintained. This is achieved by measuring pertinent water quality factors and adding chemicals or water to keep the factors within acceptable parameters.

 WATER BALANCE

Water is constantly changing. Anything and everything directly and indirectly affects the relationship of its chemical parameters to each other: sunlight, wind, rain, oil, dirt, cosmetics, other bodily wastes, and any chemicals you add to it. Balanced water not only keeps swimmers comfortable, but also protects the pool shell, plumbing, and all other related equipment from damage by etching or build-up and stains.

The pool professional is already well acquainted with pH, Total Alkalinity (TA), and Calcium Hardness (CH); along with Total Dissolved Solids (TDS) and Temperature, these are the factors that influence water balance. Water that is in balance is neither aggressive nor oversaturated. Aggressive water lacks sufficient calcium to saturate the water, so it is hungry for more. It will eat anything it comes into contact with to fill its need, including the walls of your pool or spa or the equipment it touches. Over-saturated water cannot hold any more minerals, so dissolved minerals come out of solution and form scale on pool and equipment surfaces.

The pH of pool water is critical to the effectiveness of the sanitizer as well as the water balance. pH is determined by the concentration of Hydrogen ions in a specific volume of water. It is measured on a scale of 0-14, 0-7 being acidic and 7-14 being basic.

You must maintain the pH of the water at a level that assures the sanitizer works effectively and at the same time protects the pool shell and equipment from corrosion or scaling and the bathers from discomfort or irritation. If the pH is too high, the water is out of balance, and the sanitizer’s ability to work decreases. More and more sanitizer is then needed to maintain the proper level to kill off germs. Additionally, pH profoundly affects what and how much chemical must be added to control the balance. A pH of between 7.2 – 7.6 is desirable in most cases.*

As one of the most important pool water balance and sanitation factors, pH should be checked hourly in most commercial pools.* Even if you have an automatic chemical monitor/controller on your system, you need to double- check its readings with an independent pH test. With salt- water pools, pH level goes up fast, so you need to check it more often. Tests are available that require reagents and subjective evaluation of color depth and hue to judge their pH. But different users interpret these tests differently, and results can vary wildly. The PooLPRo and ULTRAPEN PT2 give instant lab-accurate, precise, easy-to-use, objective pH measurements, invaluable in correctly determining what and how much chemical to add to maintain water balance and effective sanitizer residuals.

Total Alkalinity (TA) is the sum of all the alkaline minerals in the water, primarily in bicarbonate form in swimming pools, but also as sodium, calcium, magnesium, and potassium carbonates and hydroxides, and affects pH directly through buffering. The greater the Total Alkalinity, the more stable the pH. In general, TA should be maintained at 80 – 120 parts per million (ppm) for concrete pools to keep the pH stable.* Maintaining a low TA not only causes pH bounce, but also corrosion and staining of pool walls and eye irritation. Maintaining a high TA causes overstabilization of the water, creating high acid demands, formation of bicarbonate scale, and may result in the formation of white carbonate particles (suspended solids), which clouds the water. Reducing TA requires huge amounts of effort. So the best solution to TA problems is prevention through close monitoring and controlling. The PoolPro PS9 Titration Kit features an in-cell conductometric titration for determining alkalinity.

 Calcium Hardness (CH) is the other water balance parameter pool professionals are most familiar with. CH represents the calcium content of the water and is measured in parts per million. Low CH combined with a low pH and low TA significantly increases corrosivity of water. Under these conditions, the solubility of calcium carbonate also increases. Because calcium carbonate is a major component of both plaster and marcite, these types of pool finishes will deteriorate quickly. Low CH also leads to corrosion of metal components in the pool plant, particularly in heat exchangers. Calcium carbonate usually provides a protective film on the surface of copper heat exchangers and heat sinks, but does not adversely affect the heating process. Without this protective layer, heat exchangers and associated parts can be destroyed prematurely. At the other extreme, high CH can lead to the precipitation of calcium carbonate from solution, resulting in cloudy water, the staining of structures and scaling of equipment. The recommended range for most pools is 200 – 400 ppm.* Calcium hardness should be tested at least monthly. The PoolPro  PS9 Titration Kit features an in-cell conductometric titration for determining hardness.

Total Dissolved Solids (TDS) is the sum of all solids dissolved in water. If all the water in a swimming pool was allowed to evaporate, TDS would be what was left on the bottom of the pool – like the white deposits left in a boiling pot after all the water has evaporated. Some of this dissolved material includes hardness, alkalinity, cyanuric acid, chlorides, bromides, and algaecides. TDS also includes bather wastes, such as perspiration, urine, and others. TDS is often confused with Total Suspended Solids (TSS). But TDS has no bearing on the turbidity, or cloudiness, of the water, as all the solids are truly in solution. It is TSS, or undissolved, suspended solids, present in or that precipitate out of the water that make the water cloudy.

High TDS levels do affect chlorine efficiency, algae growth, and aggressive water, but only minimally. TDS levels have the greatest bearing on bather comfort and water taste – a critical concern for commercial pool operators. At levels of over 5,000 ppm, people can taste it. At over 10,000 ppm bather towels are scratchy and mineral salts accumulate around the pool and equipment. Still some seawater pools comfortably operate with TDS levels of 32,000 ppm or more.

As methods of sanitization have changed, high TDS levels have become more and more of a problem. The best course of action is to monitor and control TDS by measuring levels and periodically draining and replacing some of your mature water with new, lower TDS tap water. This is a better option than waiting until you must drain and refill your pool, which is not allowed in some areas where water conservation is required by law. However, you can also decrease TDS with desalinization equipment as long as you compensate with Calcium Hardness. (Do not adjust water balance by moving pH beyond 7.8.)*

Regardless, you do need to measure and compensate for TDS to get the most precise saturation index and adjust your pH and Calcium Hardness levels accordingly. It is generally recommended that you adjust for TDS levels by subtracting one tenth of a saturation index unit (.1) for every 1,000 ppm TDS over 1,000 to keep your water properly balanced. When TDS levels exceed 5,000 ppm, it is recommended that you subtract half of a tenth, or one twentieth of unit (.05) per 1,000 ppm.* And as the TDS approaches that of seawater, the effect is negligible.

Hot tubs and spas have a more significant problem with TDS levels than pools. Because the bather load is relatively higher, more chemicals are added for superchlorination and sudsing along with a higher concentration of bather wastes. The increased electrical conductance that high TDS water promotes can also result in electrolysis or galvanic corrosion. Every hot water pool operator should consider a TDS analyzer as a standard piece of equipment.

A TDS analyzer is required to balance the water of any pool or spa in the most precise way. PoolPro, PoolMeter and ULTRAPEN PT1 instantly display accurate TDS levels giving you the information you need to take corrective action before TDS gets out of hand.

Temperature is the last and least significant factor in maintaining water balance. As temperature increases, the water balance tends to become more basic and scale- producing. Calcium carbonate becomes less soluble, causing it to precipitate out of solution. As temperature drops, water becomes more corrosive.

 In addition to helping determine water balance, temperature also affects bather comfort, evaporation, chlorination, and algae growth (warmer temperatures encourage growth). Myron L’s PooLPRo also precisely measures temperature to one tenth of a degree at the same time any other parameter is measured.

In the pool and spa industry water balance is calculated using the Langelier Saturation Index (LSI) formula:

SI = (pH + TF + CF + AF ) – 12.1

Where:

PH = pH value

TF = 0.0117 x Temperature value – 0.4116 CF = 0.4341 x ln(Hardness value) – 0.3926 AF = 0.4341 x ln(Alkalinity value) – 0.0074

The following is a general industry guideline for interpreting LSI values:

•   An index between -0.5 and +0.5 is acceptable pool water.

  • An index of more than +0.5 is scale-forming.
  • An index below -0.5 is corrosive.

pH, Total Alkalinity, and Calcium Hardness are the largest contributors to water balance. Pool water will often be balanced if these factors are kept within the recommended ranges.

The PoolPro PS9 Titration Kit features an LSI function that steps you through alkalinity & hardness titrations and pH & temperature measurements to quickly and accurately determine LSI. An LSI calculator allows you to manipulate pH, alkalinity, hardness and temperature values in the equation to determine water balance adjustments on the spot.

SANITATION

The most immediate concern of anyone monitoring and maintaining a pool is the effectiveness of the sanitizer – the germ-killer. There are many types of sanitizers, the most common being chlorine in swimming pools and bromine in hot tubs and spas. The effectiveness of the sanitizer is directly related to the pH and, to a lesser degree, the other factors influencing water balance.

To have true chemical control, you need to monitor both the sanitizer residual and the pH and use that information to chemically treat the water. To check chlorine residual, free chlorine measurements are made. For automatic chlorine dosing systems, ORP must also be monitored to ensure proper functioning.

Free Chlorine is the amount of chlorine available as hypochlorous acid (HOCl-) and hypochlorite ion (OCl-), the concentrations of which are directly dependent on pH and temperature. pH is maintained at the level of greatest concentration of HOCl- because hypochlorous acid is a much more powerful sanitizer than hypochlorite ion. Free chlorine testing is usually required before and after opening of commercial pools. Samples should be taken at various locations to ensure even distribution. Residual levels are generally kept between 1-2 mg/L or ppm.* PooLPRo V.4.03 and later features the ability to measure ppm free chlorine in pools and spas sanitized by chlorine only. With this feature PoolPro can measure a dynamic range of chlorine concentrations wider than that of a colorimetric test kit with a greater degree of accuracy.

ORP stands for Oxidation Reduction Potential (or REDOX ) of the water and is measured in millivolts (mV). The higher the ORP, the greater the killing power of all sanitizers, not just free chlorine, in the water. ORP is the only practical method available to monitor sanitizer effectiveness. Thus, every true system of automatic chemical control depends on ORP to work.

The required ORP for disinfection will vary slightly between disinfecting systems and is also dependent on the basic water supply potential, which must be assessed and taken into account when the control system is initialized. 650 mV to 700 – 750 mV is generally considered ideal.*

Electronic controllers can  be inaccurate and inconsistent when confronted with certain unique water qualities, so it is critical to perform manual testing with separate instrumentation. For automatic control dosing, it is generally recommended that you manually test pH and ORP prior to opening and then once during the day to confirm automatic readings.*

Samples for confirming automatic control dosing should be taken from a sample tap strategically located on the return line as close as possible to the probes in accordance with the manufacturer’s instructions. If manual and automatic readings consistently move further apart or closer together, you should investigate the reason for the difference.*

ORP readings can only be obtained with an electronic instrument. PoolPro provides the fastest, most precise, easy-to-use method of obtaining ORP readings to check the effectiveness of the sanitizer in any pool or spa. This is the best way to determine how safe your water is at any given moment.

SALTWATER SANITATION

A relatively new development, saltwater pools use regular salt, sodium chloride, to form chlorine with an electrical current much in the same way liquid bleach is made. As chlorine – the sanitizer – is made from the salt in the water, it is critical to maintain the salt concentration at the appropriate levels to produce an adequate level of sanitizer. It is even more important to test water parameters frequently in these types of pools and spas, as saltwater does not have the ability to respond adequately to shock loadings (superchlorination treatments).

Most saltwater chlorinators require a 2,500 – 3,000 ppm salt concentration in the water (though some may require as high as 5,000-7,000 ppm).* This can barely be tasted, but provides enough salt for the system to produce the chlorine needed to sanitize the water.

(It is important to have a good stabilizer level – 30 – 50 ppm* – in the pool, or the sunlight will burn up the chlorine. Without it, the saltwater system may not be able to keep up with the demand regardless of salt concentration.)

Taste and salt shortages are of little concern to seawater systems that maintain an average of 32,000 ppm. In these high-salt environments, you need to beware of corrosion to system components that can distort salt level and other parameter readings.

Additionally, incorrect salt concentration readings can occur in any saltwater system. The monitoring/controlling components can and do fail or become scaled— sometimes giving a false low salt reading. Thus, you must test manually for salt concentration with separate instrumentation before adding salt.

You must also test salt concentration manually with separate instrumentation to re-calibrate your system. This is critical to system functioning and production of required chlorine. Both the PoolPro and PT1 conveniently test for salt concentration at the press of a button as a check against automatic controller systems that may have disabled equipment or need to be re-calibrated.

Though no one instrument or method can be used to determine ALL of the factors that affect the comfort and sanitation of pool and spa water, PoolPro is a comprehensive water testing instrument that is reliable durable, easy-to-use and easy-to-maintain and calibrate. As a pool professional, a PoolPro will not only simplify your life, it will save you time and money.

 RECORD KEEPING – WHAT TO DO WITH ALL THOSE MEASUREMENTS …

Data handling should be done objectively, and data recorded in a common format in the most accurate way. Also, data should be stored in more than one permanent location and made available for future analysis. Most municipalities require commercial aquatic facilities to keep permanent records on site and available for inspection at any time.

PoolPro makes it easy to comply with record keeping requirements. The PoolPro is an objective means to test free chlorine, ORP, pH, TDS, temperature and the mineral/salt content of any pool or spa. You just rinse and fill the cell cup by submerging the waterproof unit and press the button of the parameter you wish to measure. You immediately get a standard, numerical digital readout –  no interpretation required – eliminating all subjectivity. And model PS9TK features the added ability to perform in-cell conductometric titrations for Alkalinity, Hardness and LSI on the spot. Up to 100 date-time-stamped readings can be stored in memory and then later transferred directly to a computer wirelessly using the bluDock™ accessory package. Simply pair the bluDock with your computer, then open the U2CI software application to download data. The user never touches the data, reducing the potential for human error in transcription. The data can then be imported into any program necessary for record-keeping and analysis. The bluDock is a quick and easy way to keep records that comply with governing standards.*

*Consult your governing bodies for specific testing, chemical concentrations, and all other guidelines and requirements. The ranges and methods suggested here are meant as general examples.

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Categories : Case Studies & Application Stories, Product 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.



WIKIPEDIA AND MATERIAL FROM IWA WATER WIKI BY HTTP://WWW.IWAWATERWIKI.ORG IS LICENSED UNDER A CREATIVE COMMONS ATTRIBUTION-SHARE ALIKE 3.0 UNPORTED LICENSE.
Categories : Science and Industry Updates

Frequently Asked Questions – MyronLMeters.com

Posted by 28 Jan, 2013

TweetHow long will my Standard Solutions and Buffers last? The warranty on all standards and buffers is one year from the date it is manufactured (see the label on the bottle). If the standards and buffers become contaminated by the user pouring test samples back into the bottle or inserting the probe into the bottle […]

How long will my Standard Solutions and Buffers last?

The warranty on all standards and buffers is one year from the date it is manufactured (see the label on the bottle). If the standards and buffers become contaminated by the user pouring test samples back into the bottle or inserting the probe into the bottle the solution will not be accurate and should be discarded. The life of standards and buffers can exceed 1 year if the bottle is stored tightly capped and is not exposed to direct sunlight or freezing temperatures. If the solution becomes frozen, do not remove the cap – allow the standard or buffer solution to thaw completely and shake the bottle vigorously before opening.

How do I clean the conductivity cell cup on the handheld units?

With everyday sampling, the cell cup may build up a residue or film on the cell walls that may cause the readings to become erratic. Use a 50/50 mixture of a common household cleaner (i.e. Lime-A-Way, CLR, Tilex, etc) and DI water. Pour into conductivity cell cup and scrub with a q-tip. Be sure to get around all the electrodes and the thermistor probe. On the DS handheld unit, use an acid brush to scrub the cell cup. Let it set for about 10 minutes. Rinse the cell cup thoroughly with tap water, then a final rinse with DI water.

The display on my Ultrameter II 6P reads “Error 1″. What does that mean?

This is possibly caused by contamination to the circuit board. One or more of the traces on the PCB have been jumped/bridged and there is a contamination. Possible moisture, condensation, dirt, dried salts or other condensation inside is a potential cause for this display.

Where can I get an operations manual for my meter?

Go to MyronLMeters.com. Click on Manuals and Literature at the top of the page. Once on the Manuals and Literature page, you’ll find application bulletins, operations manuals, material safety data sheets, and product datasheets.  All are free, downloadable pdf files.

How do I pick the correct range module for my Monitor or Monitor/Controller?

Pick a range module that covers 2/3 of your operating range. If you pick a range module that is too broad, then your accuracy will suffer or it will not show a number on the display. For example, if your operating range is 100-150 microsiemens, a range module of 0-200 microsiemens (-115) would be a good choice. A range module of 0- 5,000 microsiemens (-123) would not be a good choice for this application

Got questions? Visit us at MyronLMeters.com and Ask An Expert.

 

 

 

 

Categories : Application Advice, Care and Maintenance, Product Updates, Technical Tips

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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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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