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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.
Water Filter Media Glass media and Sand Glass is aluminosilicate manufactured from silica sand or from the re-melt of glass bottles. It has a similar chemical composition to sand, but may contain metal oxides such as aluminium, or ferric to make amber glass or manganese and chromium for green glass. Glass as a filter media was used in 1984 by Dr Howard Dryden as an alternative to the zeolite clinoptilolite as a means of filtering water in a RAS (Recirculating Aquaculture System) for eels and Atlantic salmon. The glass was initially used as a feedstock for the manufacture of synthetic zeolites. the glass was subsequently used as a substrate and the surface of the glass was changed by a solgel process to give it a bydrohilic high surface area to avoid bio fouling while still acting as a molecular sieve similar to clinoptilolite for the adsorption of organics. The manufacturer of filter media provides an opportunity to make a filter media with a specific tailored performance. The performance then can be quantified and compared against other filter media. Such an investigation has never been conducted for sand. Given that sand is used to treat more than 99 percentage of our drinking water supply, it is rather surprising that there has been no detailed comparison of sand media performance from different deposits or different countries.
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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.
Water Filter Media Green Water Concepts India Pvt Ltd is one of the largest supplier of different kind of superior quality water filter media. Filter Sands: Different kind of pebbles and filter sand are available at Green Water Concepts India Pvt Ltd. Activated Carbon: Granular Activated Carbon (IV range, 900 - 1200), of reputable manufactures are available at GWC . Iron Removal Media Superior quality Manganese dioxide with high manganese content is also available at GWC. Katalox Light, Purolite MZ Plus, BIRM etc are also available at GWC. Softener Resin, Indion 220Na is also avaliable at GWC.