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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.
Iron Removal Plants Iron removal plants can be based on different filtration media, depending on the iron and manganese concentration, the oxygen level, CO2 content and hardness of the water. Plant principle: First, air is injected in order to oxidize the iron. The oxidized iron will then precipitate on a sand filter. An MnO2 layer in the sand bed will catalyze the oxidation of residual iron. Backwash will be done by water and by air. More on iron removal principles Iron removal plant flow diagram:
Water borne diseases are caused by the pathogenic microorganisms that are transmitted in the contaminated fresh water. Waterborne infection can be caused by drinking polluted water and even by consuming the food that is infected with pathogens. It has been reported that half of India’s mortality is caused due to waterborne diseases. Amongst the water-related diseases in India, diarrhea is the most prevalent and top on the list. Malaria and cholera are the waterborne diseases that thousands of people fall prey to it. Different Types of Waterborne Diseases and their Symptoms There are numerous harmful bacteria, virus, chemical pollutants and dissolved impurities that are present in the contaminated water. Such pathogens are not even visible to us through naked eyes and thus, when we drink the impure water we fall sick. There are many cities that do not have water treatment facilities and in this concern, people are knowingly or unknowingly consuming polluted water that is supplied to their home. It is the water-related diseases and the scarcity of the clean water that are the main cause of deaths in both the urban and rural areas. Cholera: Cholera is a waterborne disease and is diarrhoeal in nature. A person can get affected by Cholera by drinking water or eating food contaminated with the cholera bacterium. Thousands of people fall prey to this disease every year and many lose their lives as well. It can happen to both children and adults and some of the symptoms of cholera include vomiting, abdominal cramps, watery bowels, and fever. Typhoid: It is another disease that gets transmitted by drinking contaminated water that carries ‘Salmonellae Typhi bacteria’. Some of the symptoms through which you can understand that you are being affected by Typhoid are prolonged fever, loss of appetite, headache, constipation, exhaustion, sleepiness, and nausea. It can also be transmitted by close contact with the infected person. Diarrhoea: Diarrhoea is one of the most common waterborne diseases that mostly affects children under the age of 5. The infection of diarrhea spreads through eating contaminated food and impure water. Some of the symptoms of diarrhea include dehydration, severe dizziness, loss of consciousness, pale skin and bloody stool, little or no urination. The attack of diarrhea can last up to 2 weeks by leaving the person dehydrated and if kept untreated the infected person can lose his/her life as well. Hepatitis A: Another type of waterborne diseases is Hepatitis A and it is caused by Hepatitis A virus, which affects the liver. It is normally spread by the fecal-oral route, by direct contact with the infected person or by ingestion of the contaminated food or water. Some of the symptoms that you can find in the infected person are nausea, vomiting, and fever. Amebiasis: Amebiasis is a kind of parasitic infection in the intestine that is caused by the protozoan Entamoeba histolytica, or E. histolytica. The single-celled protozoan usually enters the human body when the person swallows cysts through food or water. Cysts are an inactive form of parasite that stays alive for several months in the soil or environment, especially in the feces. So, you can say that the parasite can also enter the body through direct contact with fecal matter. Some of the symptoms of amebiasis are the loose stool, stomach pain, and abdominal cramping. Campylobacteriosis: Under the list of waterborne diseases, Campylobacteriosis is another infection, which is caused by the Campylobacter bacterium, most commonly known as C. jejuni. Campylobacteriosis is the most common bacterial infections produces an inflammatory in the body. It can sometimes cause bloody diarrhea or dysentery syndrome like fever and pain. Giardiasis: Giardiasis is another kind of infection that is caused in the small intestine. It is mainly caused by a microscopic parasite that is called as Giardia lamblia. Giardiasis infection gets mainly spread through the contact with the infected people and even by eating contaminated food or drinking contaminated water. Some of the symptoms of Giardiasis are Fatigue, Nausea, Vomiting, excessive gas, abdominal pain, and headaches. Viral Gastroenteritis: Viral Gastroenteritis is a kind of inflammation of the stomach and intestines, which can be caused by any number of viruses. It is a kind of contagious illness that is spread when you stay close with people who are infected with it. It can be spread by eating contaminated food or by drinking impure water. Some of the symptoms of Viral Gastroenteritis include watery diarrhea, fever, chills, headache, nausea, vomiting, abdominal pain and etc. Anyone can get affected by these water-borne diseases especially young children and pregnant women are more susceptible to them. Prevention of water-borne diseases requires many necessary precautions which include removal of impurities from water, avoiding consumption of unhygienic water, drink filtered water and much more.
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.