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UV System WHAT IS UV DISINFECTION SYSTEM AND HOW DOES IT WORK? UV Disinfection System is an extremely effective way to combat microbial contamination in water. However, microbes have to be exposed to UV-C light in the proper amount in order to effectively disinfect the water. UV Disinfection Systems are used in many different applications ranging from the purification of drinking water in individual homes to disinfecting water supply of entire townships. UV treatment for water is recognized as the safer and more cost-effective way to disinfect water for industrial applications. UV sanitization is useful in almost any application where microbial free, safe and pure water is required; and where there is a chance of the water being contaminated before it reaches the final point of use. How Does UV Disinfection System Work? UV light disinfects by penetrating microorganisms and destroying their DNA. DNA plays an important role in organisms’ functions and reproduction hence destroying the DNA prevents the organism from being active and multiplying. This UV energy (wavelength of 240-280 nm) is also naturally found in sunlight in very small quantities. The same energy is produced in stronger intensities with help of high mercury discharge lamps, commonly known as UV lamps. No bacteria, viruses, molds or their spores can survive when exposed to the correct dose of UV light. Therefore UV is considered as the best solution for water sterilization. Industrial Applications of UV Disinfection System Ultraviolet disinfection system is not simply a lamp inside a pipe. The UV Reactor must be designed to ensure that all microbes receive sufficient exposure to the UV light (dose).Based on the hydraulic properties of water; the reactor needs to be optimized to guide the flow in a manner so as to maximize residence time and boost turbulence. Well designed UV systems are producing consistently exceptional results in the industrial applications. Few Examples : Food and Beverage – UV disinfection system can help to achieve quality of water as per specifications laid down by the FDA ( Food and Drug Administration ) Bio- Pharmaceutical – Water used in Pharmaceutical and healthcare products and for CIP (Cleaning in Place) must be free of chemicals like chlorine, ozone, and pathogens. Most pharmaceutical companies depend on UV systems for water disinfection. Cosmetics – Water that is free of microorganisms and toxins ensure quality and enhance the shelf life of cosmetics. UV Sterilization is the preferred choice for the cosmetic industry across the globe. Centralized Drinking Water – A UV system is an easy, affordable solution to ensure pure water in each and every tap of your home or office. Waste Water Disinfection and Reuse – To combat the problems of water scarcity and rising cost of fresh water, UV Disinfection can help by treating the waste water in the tertiary stage. UV systems that are specially designed for wastewater can thus disinfect wastewater so that the water can be reused for secondary purposes such as flushing and gardening. Swimming Pools – Traditionally, chlorine has been in use to ensure clean water in swimming pools. However, it is increasingly being known that with chemical disinfection, chemical reacts with many other organic matters to form hundreds of new chemicals which are harmful. While UV is recognized as safer and more cost effective way to disinfect swimming pools. Benefits of UV Disinfection System Natural – UV is nature’s way of purification. Environmentally Friendly – No Toxic by-products are formed during UV disinfection process Effective – All known microorganisms are susceptible to UV light Economical – Lowest operating cost amongst disinfection systems Safe& Chemical Free – No addition of chemicals hence no danger of overdosing Fast – It is In-contact purification therefore Instant Easy to Manage – Well designed systems like the Alfaa UV systems come with many advanced features like CFD (Computational Fluid Dynamics), high-efficiency electronic ballasts, and extremely precise UV intensity monitors which make them highly effective and hence easy to manage. Does a UV Disinfection System need periodic maintenance? There can be some cases where the water is not adequately pre-treated and turbidity levels are low. In such cases, routine inspection and cleaning can be carried out every 6 months. In the case of high turbidity and hardness, the cleaning frequency might need to be increased. Finally, the UV lamp has a limited life and must be replaced once it is exhausted. In the unlikely event of premature failure of the lamp, the monitoring circuit will provide the signal to advise replacement.
How to select the right water purifier When it comes to caring for your family, you need to avoid taking impulsive decisions. One of the important decisions that you need to make is buying the right water purifier. Though it may seem quite easy to buy a water purifier, there are a number of factors that you need to consider. The water purifier that you choose depends on the quality of water you receive in the area. In addition, you need to consider the technologies used and read the water purifier reviews before making the final decision. If you too are planning to buy the best water purifier here are some important factors you need to consider. How to choose the best water purifier for home You should consider the below mentioned points whilst purchasing a water purifier. Water Quality As already mentioned, you need to check the water quality before buying a purifier. If water in your area has a high TDS level, hardness and salinity, you need to opt for an RO water purifier. RO water purifiers come with a semi-permeable membrane which can remove the dissolved salts, metals and impurities. Types of Water Purifier There are different water purification technologies available in the market. Understanding the various water purifier technologies is very important in order to make the right decision. Depending on the water quality and budget, you can choose among RO, UV, and UF (gravity based) water purifiers. Here are some more details about the various technologies. RO Water Purifiers Reverse Osmosis Purifiers are ideal for areas that have high TDS level. RO water purifiers can remove heavy metals, Fluoride, Arsenic, and other toxic impurities from water. However, RO purifiers also remove some of the essential minerals from water which can be supplemented by mineral addition system. Gravity Based Water Purifiers UF Water Purifier for low TDS water Gravity based water purifiers are budget-friendly and don’t require power to operate. You can use gravity based water purifiers if the TDS level in your area is low. The water purifiers are ideal for removing bacteria, dust, chlorine and cysts from water. UV Water Purifiers UV Water Purifier UV water purifiers use a high power UV lamp to disinfect the water, the UV purifier does not remove other physical or chemical impurities from the water. Contamination Contaminants Present in Water Bacteria, nitrate, dissolved pesticides, and lead are some of the common contaminants present in water. The amount of contaminants present in water can be tested in any laboratory. If water supplied to your home is high in microbes and contaminants, you need to install a RO+UV+UF filtration as an intelligent choice. The UV effects irradiate the water and penetrate the cells of bacteria and viruses, destroying their ability to reproduce. These organisms fail to multiply and eventually die. The RO membrane removes these dead germs and contaminants from water and makes it fit for consumption. Storage Capacity When buying a water purifier, it is very important to take into account the storage capacity. If you live in an area which is prone to power cuts, you need a water purifier which has a higher storage capacity. The automated water purifiers start the purification process as soon as the water level in the purifier declines. Certifications Another important factor that you need to check in water purifier reviews is the certifications received by the brand. Certified water purifiers ensure that the brand is authentic and trustworthy. ISI and WQIA (Water Quality Association of India) the Indian certification bodies, NSF, WQA, IBWA etc. are International certification bodies. Maintenance and After Sales Services Lastly, before making the final decision, ensure that you get all the necessary information about maintenance and after-sales services of water purifiers. A water purifier that needs frequent maintenance services is not worth the money you invest. In addition, you also need to check the after sales services provided by the company. Poor after sales services lead to a lot of problems if something goes wrong with the water purifier.
Green Water Concepts India Pvt Ltd has signed an agreement with Kottopadam Grama Panchayat for the supply, installation, and commissioning of UV water purifiers, 500LPH capacity. GWC has successfully installed 18 nos of UV water purifiers with auto cut off facility. The purifying units consists of 1. Sediment Filter - 5 micron, 20inch, with 20inch polypropylene cartridge 2. Carbon block filter (CTO, 20') 3. Sediment Filter - 1micron, 20inch, with PP Cartridge 4. Solenoid Valve 5. UV System 500LPH - alpha UV 6. Loft Tank, 150L capacity 7. SS Taps, for dispensing the water. The UV system will cut off when the loft tank is full. The school administrative already admired the quality of the job done.
Water Chemistry, pH The technical definition of pH is that it is a measure of the activity of the hydrogen ion H plus and is reported as the reciprocal of the logarithm of the hydrogen ion activity. Therefore, a water with a pH of 7 has 10-7 moles per liter of hydrogen ions, whereas, a pH of 6 is 10-6 moles per liter. The pH scale ranges from 0 to 14. 0 acidic 7 neutral 14 basic In general, a water with a pH less than 7 is considered acidic and with a pH more than 7 is considered basic. The normal range for pH in surface water systems is 6.5 to 8.5 and for groundwater systems 6 to 8.5. Alkalinity is a measure of the capacity of the water to resists a change in pH that would tend to make the water more acidic. The measurement of alkalinity and pH is needed to determine the corrosivity of the water. The pH of pure water is 7 at 25-degree Celsius, but when exposed to the carbon dioxide in the atmosphere this equilibrium results in a pH of approximately 5.2. Because of the association of pH with atmospheric gasses and temperature, it is strongly recommended that the water be tested as soon as possible. The pH of the water is not a measure of the strength of the acidic or basic solution and alone does not provide a full picture of the characteristics or limitations of the water supply. In general, a water with a low pH, less than 6.5, could be acidic, soft, and corrosive. Therefore, the water could leach metal ions such as iron, manganese, copper, lead, and zinc from the aquifer, plumbing fixtures, and piping. Therefore, a water with a low pH could contain elevated levels of toxic metals, cause premature damage to metal piping, and have associated aesthetic problems such as a metallic or sour taste, staining of laundry, and the characteristic blue-green staining of sinks and drains . The primary way to treat the problem of low pH water is with the use of a neutralizer. The neutralizer feeds a solution into the water to prevent the water from reacting with the house plumbing or contributing to electrolytic corrosion, a typical neutralizing chemical is soda ash. Neutralizing with soda ash increases the sodium content of the water. A water with a pH greater than 8.5 could indicate that the water is hard. Hard water does not pose a health risk but can cause aesthetic problems. These problems include: Formation of a scale or precipitate on piping and fixtures causing water pressures and interior diameter of piping to decrease; Causes an alkali taste to the water and can make coffee taste bitter, Formation of a scale or deposit on dishes, utensils, and laundry basins; Difficulty in getting soaps and detergents to foam and formation of insoluble precipitates on clothing, etc. and Decreases efficiency of electric water heaters. Typically these problems are encountered when the hardness exceeds 100 to 200 milligram CaCO3 per liter which is equivalent to 12 grains per gallon. Water can be softened through the use of ion-exchange or the addition of a lime-soda ash mixture, but both processes increase the sodium content of the water. Note: The ideal pH level of alkaline ionized water for long term human consumption is between 8.5 and 9.5 with the ideal ORP value around -200mV to -300mV, and in no way significantly greater than 400mV.
Green Water Concepts India Pvt Ltd is the authorized distributor of water dispensers of Conway Water Purifier Private Ltd. Conway Water Purifier is the first company in India introduces Customized stainless steel water purifier/ water cooler / water dispenser, which are designed and developed by a team of professionals based on their 3 decades of experience in the water purification industry. Conway Water Purifier has developed over 200 customized products in the past and those are working extremely well at customer’s site and getting us repeated orders. Some of the Conway products are 1) Stainless steel water cooler with Reverse osmosis RO / Ultraviolet UV / Ozone purifiers 2) Stainless steel water purifier with Reverse osmosis RO / Ultraviolet UV / Ozone purifiers 3) Stainless steel water dispenser with Reverse osmosis RO / Ultraviolet UV / Ozone purifiers.
Green Water Concepts India Pvt ltd has signed an agreementin February 2018 with Govt. Engineering College, Kozhikode for the supply and installation of 3 units of water dispensers with hot, cold and normal. The salient features of the supplied water purifier are 1. Stainless Steel Storage Tanks, total capacity - 80L 2. Cartridge Filters in SS housing 3. UV & Ozone system for disinfection of water 4. Auto cut off features 5. Dry run protection of UV lamp The units were installed in the month of February.
Disinfectants Copper-silver ionization Metals such as copper and silver can be used for water disinfection, if they are ionized. Process history Archeological excavations show, that people have been using copper for more than 10000 years and have been using silver for more than 5000 years. Copper can be easily extracted and processed. More than 7000 years ago people developed a copper extraction mechanism for copper ores. The Roman empire gained most of its copper from Cyprus, the isle that gave copper its name. Nowadays copper is mainly extracted from ores, such as cuprite (CuO2), tenorite (CuO), malachite (CuO3•Cu(OH)2), chalcocite (Cu2S), covelite (CuS) and bornite (Cu6FeS4). Large deposits of copper ores have been found throughout the US, Chili, Zambia, Zaïre, Peru and Canada. Silver can be obtained from pure deposits, from silver ores such as argenite (Ag2S) and horn silver (AgCl) and combined with ore deposites that contain lead, gold or copper. Both copper and silver have been applied for centuries because of their biocidal mechanism. The Vickings used copper strings on their ships to prevent the growth of algae and shells. Modern ships still use the same technology. Most anti-fouling paints contain copper, reducing the number of marine species growing on the walls of ships. Because of this measure, ships can reach their destination faster. Nomads used silver coins to improve drinking water quality. Well water containing copper and silver coins is very bright, due to the biocidal effect of these metals. Since 1869 various publications have appeared on disinfection properties of silver. Some European and Russian villages have been using silver for drinking water treatment for many years. Copper-silver ionization was developed in both Europe and the United States in the 1950’s. Copper-silver ion - Process Copper-silver ionization is brought about by electrolysis. An electric current is created through copper-silver, causing positively charged copper and silver ions to form. Copper-silver ionization brings us back to basic chemistry: an ion; an electrically charged atom has a positive charge when it gives up an electron and a negative charge when it takes up an electron. A positively charged ion in called a cation and a negatively charged ion is called an anion. During ionization, atoms turn into cations or anions. When copper-silver ionization is applied, positively charged copper (Cu+ and Cu2+) and silver (Ag+) ions are formed. The electrodes are placed close together. The water that is disinfected flows past the electrodes. An electric current is created, causing the outer atoms of the electrodes to lose an electron and become positively charged. The larger part of the ions flows away through the water, before reaching the opposite electrode. Generally the amount of silver ions at a copper ion rate of 0, 15 to 0, 40 ppm lies between 5 and 50 ppb. The ion concentration is determined by the water flow. The number of ions that is released increases, when electric charges are higher. When copper ions (Cu+) dissolve in water, they are oxidized immediately to form Cu2+ ions. Copper can be found in the water in free form. It is commonly bond to water particles. Copper (Cu+) ions are unstable in water, unless a stabilizing ligand is present. Applications of copper-silver ionization Copper-silver ionization is suitable for a large number of applications. It became of interest when NASA used copper-silver ionization for drinking water production aboard Apollo space ships in 1960. The ion generator that was used was the size of a matchbox. Because of copper-silver ionization, drinking water could be produced safely in space without the use of chlorine. In England, copper-silver ionization is applied in about 120 hospitals successfully for the deactivation of Legionella bacteria. In the United States, copper-silver ionization is mainly used for swimming pool water disinfection. Copper-silver is often used to limit disinfection byproducts formation during chlorine disinfection. Because of its specific properties, copper-silver ionization is very suitable for fishpond disinfection. Copper-silver ionization is not dependent on temperatures. It is active in the entire water system. Copper-silver ionization is used by water bottling companies and companies that recycle water throughout the United States. The disinfection mechanism of copper-silver ionization Electrically charged copper ions (Cu2+) in the water search for particles of opposite polarity, such as bacteria, viruses and fungi. Positively charged copper ions form electrostatic compounds with negatively charged cell walls of microorganisms. These compounds disturb cell wall permeability and cause nutrient uptake to fail. Copper ions penetrate the cell wall and as a result they will create an entrance for silver ions (Ag+). These penetrate the core of the microorganism. Silver ions bond to various parts of the cell, such as the DNA and RNA, cellular proteins and respiratory enzymes, causing all life support systems in the cell to be immobilized. As a result, there is no more cellular growth or cell division, causing bacteria to no longer multiply and eventually die out. The ions remain active until they are absorbed by a microorganism. The disinfection applications of copper-silver ionization Swimming pools and copper-silver ionization In the United States, copper silver ionization is applied as an alternative for chlorine disinfection. Chlorine use can be reduced by 80 percent. However, another disinfectant should be added in addition to copper-silver. This is because copper-silver cannot remove organic matter, such as skin tissue, hairs, urine and skin flakes, from swimming pool water. Cooling towers and copper-silver ionization Cooling tower water requires disinfection, to prevent the growth of microorganisms. This can be brought about by a combination of copper-silver ionization and chlorine disinfection. Chlorine concentrations that are required are much lower. Copper-silver ionization can also be used to kill Legionella bacteria in cooling towers. Legionella in hospitals and nursing homes and copper-silver ionization Copper-silver ionization is applied in hospitals and nursing homes to prevent the distribution of Legionella bacteria. The main source of Legionella distribution is the warm water system. Circumstances in warm water systems are ideal for Legionella bacteria to grow and multiply. Contagion mainly takes place through shower steam. Copper-silver ionization can sufficiently kill Legionella bacteria. Copper-silver can actively deactivate Legionella, as well. Drinking water and copper-silver ionization In the United States, several drinking water production companies use copper-silver ionization as an alternative for chlorine disinfection and to prevent the formation of disinfection byproducts. The standard for trihalomethanes was decreased by EPA from 100 to 80 microgram per litre. When copper-silver ionization is combined with chlorine disinfection, it is an excellent disinfection mechanism to deactivate viruses and bacteria. What are the terms of copper-silver ionization? The affectivity of copper-silver disinfection depends on a number of factors: Firstly, the concentration of copper and silver ions in the water should be sufficient. The required concentration is determined by the water flow, the volume of water in the system, the conductivity of the water and the present concentration of microorganisms. Secondly, the electrodes should be in good condition. When the water is hard or fouling takes place as a consequence of water hardness and quality, there will be a decrease in electrode release and the additional effect will decrease. By using pure silver and pure copper, the supply of copper and silver ions can be regulated separately. These electrodes suffer from less limestone formation and fouling. Thirdly, the affectivity of copper-silver ionization depends on the pH value of the water. When pH values are high, copper ions are less effective. When the pH value exceeds 6, insoluble copper complexes will precipitate. When the pH value is 5, copper ions mainly exist as Cu(HCO3)+; when the pH value is 7 as Cu(CO3) and when the pH values is 9 as Cu(CO3)22-. Fourthly, copper-silver ionization affectivity is determined by the presence of chlorine. Chlorine causes silver chlorine complex formation. When this occurs, silver ions are no longer available for disinfection. How effective is copper-silver ionization? Copper-silver ionization can deactivate Legionella bacteria and other microorganisms in slow-running water and still water. Legionella bacteria are very susceptive to copper-silver ionization. Copper-silver ionization also takes care of bio film. Copper remains within the bio film, causing a residual effect. It appears that copper-silver ionization addition causes the number of Legionella bacteria to diminish. After a short period of time, however, the number of Legionella bacteria will rise again because they can also be found in the bio film. Copper that stays behind in the bio film takes care of these bacteria. When copper and silver ions are added to water constantly, the concentration of Legionella bacteria remains low. The deactivation rate of copper-silver ionization is lower than that of ozone or UV. A benefit of copper-silver ionization is that ions remain in the water for a long period of time. This causes long-term disinfection and protection from recontaminations. Copper and silver ions remain in the water until they precipitate or absorb to bacteria or algae, and are removed from water by filtration after that. The benefits and drawbacks of copper-silver ionization Benefits Copper-silver ionization affectively deactivates Legionella bacteria and bio film and it improves water quality. Copper-silver ionization has a larger residual effect than most other disinfectants. Copper and silver ions remain in the water for a long period of time. Because of its local affectivity, the effect is larger than that of UV. Copper-silver is effective throughout the entire water system, even in dead-end points and parts of the system that contain slow-running water. Copper-silver use affectivity does not depend on water temperature. When copper-silver is used, less maintenance to the water system is required. Copper-silver is non-corrosive; it causes less strain on the distribution system. Because of a decrease in the use of chemicals, the lids and pumps are not affected. Furthermore, shower heads, tanks and taps are not contaminated. When copper-silver ionization is applied, there are no transport and storage difficulties. Drawbacks Copper-silver affectivity depends on the pH value of the water. At a pH value of 9, only one tenth of all Legionella bacteria are removed. When dissolved solid concentrations are high, silver will precipitate. This means silver ions are no longer available for disinfection. Silver ions easily react with chlorines and nitrates that are present in the water, causing them to no longer be effective. Some species of microorganisms can become resistant to silver ions. They can remove metal from their systems or convert it to a less toxic product. These microorganisms can become resistant to copper-silver ionization. Although it is suggested that Legionella bacteria can develop resistance to copper-silver ionization, this disinfectant still appears to be effective for Legionella deactivation. To affectively kill pathogenic microorganisms, copper and silver ions should be present in the entire water system. When the system is used little and the water flow is quite slow, or when there are dead-end points in the system, this can causes problems for disinfection. The health effects of copper-silver ionization Insufficient evidence have been found on the possible health effects of long-term exposure to copper-silver ionization. Little is known on the general health effects of copper-silver ionization. Legislation for copper-silver ionization EU The European Union does not dictate any standards considering silver concentrations in the water. Copper, however, has a maximum value of 20 μg/L, because it corrodes waterworks. Copper concentrations should be measured in taps. (EU Drinking water directive 98/83/EC, 1998) WHO The WHO does not dictate any standards considering the concentration of silver as a drinking water disinfectant, because the organization found the available data to be insufficient to recommend a health standard. (WHO, Guidelines drinking water quality, 3e editie) USA The United States dictate a maximum value of 1 mg/L of copper and a maximum value of 0, 1 mg/L of silver. (EPA, National Secondary Drinking Water regulations, 2002) How is copper-silver ionization controlled? When copper-silver ionization is applied, a log of the entire system must be kept. Water analysis and tests must be conducted to prove system affectivity, because this concerns an alternative disinfectant. The first analysis round takes place before the application of copper-silver ionization. Copper and silver concentrations in the water are measured and the amount of Legionella bacteria and the aerobic growth number at 22 ˚C and at 37 ˚C are determined. When the system is placed, the outcome of water analysis should be checked and reported monthly.
Chemistry of Iron Removal Iron is one of the most abundant metals of the Earth's crust. It occurs naturally in water in soluble form as the ferrous iron or complexed form like the ferric iron (trivalent iron: Fe3+ or precipitated as Fe(OH)3). The occurrence of iron in water can also have an industrial origin ; mining, iron and steel industry, metals corrosion, etc. In general, iron does not present a danger to human health or the environment, but it brings unpleasantness of an aesthetic and organoleptic nature. Indeed, iron gives a rust color to the water, which can stain linen, sanitary facilities or even food industry products. Iron also gives a metallic taste to water, making it unpleasant for consumption. It can also be at the origin of corrosion in drains sewers, due to the development of microorganisms, the ferro-bacteries. In aerated water, the redox potential of the water is such as it allows an oxidation of the ferrous iron in ferric iron which precipitates then in iron hydroxide, Fe(OH)3, thus allowing a natural removal of dissolved iron. 4 Fe2+ 3 O2 --> 2 Fe2O3 Fe2O3 + 3 H2O --> 2Fe(OH)3 The form of iron in water depends on the water pH and redox potential. Usually groundwater has a low oxygen content, thus a low redox potential and low pH (5.0- 6.5) Pourbaix diagram of Iron However ground waters are naturally anaerobic: so iron remains in solution and therefore it is important to remove it for a water use. The elimination of the ferrous iron, by physical-chemical way, is obtained by raising the water redox potential by oxidation thanks and this by simple ventilation. In the case of acid water, the treatment could be supplemented by a correction of the pH. Thus, the ferrous iron is oxidized in ferric iron, which precipitates in iron hydroxide, Fe (OH)3. The precipitate is then separated from water by turbidity removal filter or decantation. The stage of precipitation by chemical oxidation can also be carried out with the stronger oxidants such as sodium hypochlorite (NaOCl), chlorine dioxide (ClO2), ozone (O3) or the potassium permanganate (KMnO4). This elimination can be carried out by cascade or spraying open-air systems (for an acceptable maximum content of Fe2+ of 7mg.L-1) known as gravitating systems. Those systems require a significant place on the ground, but, in addition to an easy and a cheap exploitation cost, they also make possible aggressive CO2 and hydrogen sulfide (H2S) removal. There are also pressure systems, which in addition to their compactness, make possible to treat water whose Fe2+ concentrations between 7 and 10mg.L-1. Iron removal system schema Iron is often found in water in complexed forms. In order to be eliminated, iron complexed requests a coagulation stage, which comes in between oxidation and filtration. Remark : It is possible to remove iron from water by biological way. Indeed, there are many bacteria, whose metabolism and thus their survival, are related to the oxidation of iron. However this biological removal requires conditions specific for the pH, the temperature, the redox potential, etc.
AFM, Glass Media and Sand Filtration Systems, a Comparison of Technologies and Optimization of Performance. Media Bed mechanical sand filtration systems comprise of, gravity flow, pressure, and moving bed continuous backwash filtration systems. In all cases, the most common mechanical filtration media is quartz silica sand. The quality of quartz sand is a variable depending upon the country and the location of the deposit. There is a requirement for a consistent quality of filter media for all industries using media bed filtration in order to standardize and optimize the filtration process. This aspect becomes more important for filters, that have a pressure gradient across the bed such as horizontal filters, or filters that have not been installed on a perfectly level base. The performances of seven different types of filtration media were physically evaluated by IFTS (1) one of the leading independent accredited laboratories in Europe for the evaluation of products used by the water industry. History Sand has been used for over 200 years in Europe as a means of filtering Drinking water. A company in Scotland in 1804 was the first documented report of a company using sand in a slow bed sand filter (2). Slow bed sand filters typically operate at water flow velocity of 0.1m/hr and use a coarse grade of sand and gravel. The filters depend on the maturation of the sand as a biological filter before they provide adequate mechanical water filtration. Slow bed sand filters provide excellent water quality and are still used for the treatment of drinking water. Approximately 15 percent of all water supplies in the UK currently use slow bed filters, but they are being phased out in favor of RGF (Rapid Gravity Filters) and pressure sand filters in order to save space. RGF filters for drinking water operate at water flow velocity of 6m/hr whereas pressure filters typically operate at 12m/hr. The water flow velocities of RGF and pressure filters are therefore 60 to 120 times faster than slow bed filters. The higher water velocities change the bio-dynamics of the filtration process which impacts on filter performance leading to bio-instability and transient wormhole channeling of unfiltered water through the filter bed. The performance of any media bed will be inversely proportional to the flow velocity, which is a function of the filter diameter, its surface area and bed depth. The bar graph compares the performance of AFM and Leighton Buzzard sand from England. The slower the filter flow velocity the higher the performance, the relationship is exponential but the coefficient depends on the media characteristics and particle size used for performance evaluation. One of the key issues in the drinking water industry is the ability to remove a parasite called Cryptosporidium, which is almost completely resistant to chlorine and only measures 4 micron in size. If sand filters are operated at water flows in excess of 12m/hr it becomes increasingly difficult to ensure adequate water quality and the removal of parasite. Water treatment system tend to operate at the highest possible water flow rates in order to save space and reduce capital cost. AFM has been shown to provide performance advantages over sand, which permits higher water flow rates and reduced capital cost of illustrations. Typically 50% higher water flow rates can be used with AFM over sand while still maintaining good performance. Filtration performance also depends upon filter configuration; horizontal filters save space and maximize surface area. Bed depth is shallower which reduces absorption capacity for small particles. Also, a differential pressure gradient across the bed reduces performance when compared to vertical filters that have a consistent pressure gradient and a deep bed. The differential pressure promotes biofouling of sand, biodynamic instability and transient wormhole channeling; the problems are largely resolved by using AFM which does not suffer from biofouling. Pressure Differential During the run-phase large solids will accumulate on the top of the filter bed and small solids will penetrate the bed. Small particles attracted by electrical (Van Der Waals) forces may become trapped on the surface of the media. Sand and most media carry a negative charge on Zeta Potential. In water treatment, coagulants and flocculants such as; Lanthanum chloride, aluminium chloride, ferric chloride, PAC (polyaluminium chloride) or polyelectrolytes may be applied to drop the zeta potential, increase coagulation and flocculation as well as increasing electrical attraction. In some industries including pre-treatment prior to membranes or the aquarium industry, the use of chemicals would not be advisable. Reduction of the zeta potential and coagulation can nevertheless be achieved by the rapid movement of water, cavitating static mixers. In addition to mechanical and electrical attraction, there will also be some degree of molecular sieve filtration. This will be the case with activated carbon, and to a lesser extent with new sand. The ability of sand to adsorb is a function of the silicon to aluminium ratio and how the molecules are configured. An example of natural ion exchange molecular sieve sand is the zeolitic sand clinoptilolite. Zeolites are used in water treatment as a mechanical filtration media and also as an ion exchange mineral for the selective removal of ammonium and radioactive nuleotides from freshwater. Zeolites cannot be used for marine systems or water with a high TDS because the competing cation will prevent ion exchange. In freshwater systems zeolites provide a good substrate for the growth of autotrophic nitrifying bacteria, a characteristic that is likely due to the adsorption of ammonium into the mineral and its availability to be metabolized by autotrophic species such as Nitrosomonas spp.
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