Filter Selection Data
REMOVAL Application

Silica Sand

Suspended Solids




Iron & Manganese

Manganese Dioxide

Iron & Manganese

Manganese Green Sand

Iron & Manganese

Activated Carbon

taste, odour, colour, chlorine, organics

Typical Application The following are types of filters and their usage: Dual Media Sand Filter : This filter is used to remove turbidity and suspended solids from raw water. Media implemented is Silica Sand & Anthracite with standard filtration rate of 10m³/hr/m² Iron/Manganese Removal Filter : This filter is used to remove iron and manganese from the raw water with different feed water pH at standard filtration rate of 10-12m³/hr/m². Activated Carbon Filter : This filter is specially designed for the absorption of soluble organic impurities found in water. SAND FILTER DESCRIPTION Sand filters have proven effective in removing several common pollutants from storm water runoff. Sand filters generally control storm water quality, providing very limited flow rate control. A typical sand filter system consists of two or three chambers or basins. The first is the sedimentation chamber, which removes floatables and heavy sediments. The second is the filtration chamber, which removes additional pollutants by filtering the runoff through a sand bed. The third is the discharge chamber. The treated filtrate normally is then discharged through an underdrain system either to a storm drainage system or directly to surface waters. Sand filters take up little space and can be used on highly developed sites and sites with steep slopes. They can be added to retrofit existing sites. Sand filters are able to achieve high removal efficiencies for sediment, biochemical oxygen demand (BOD), and fecal coliform bacteria. Total metal removal, however, is moderate, and nutrient removal is often low. APPLICABILITY Sand filters are intended primarily for water quality enhancement. In general, sand filters are preferred over infiltration practices, such as infiltration trenches, when contamination of groundwater with conventional pollutants – BOD, suspended solids, and fecal coliform – is of concern. This usually occurs in areas where underlying soils alone cannot treat runoff adequately – or ground water tables are high. In most cases, sand filters can be constructed with impermeable basin or chamber bottoms, which help to collect, treat, and release runoff to a storm drainage system or directly to surface water with no contact between contaminated runoff and groundwater. In general, sand filters can be used as alternatives for water quality inlets. They are more frequently used to treat runoff contaminated with oil and grease from drainage areas with heavy vehicle usage. In regions where evaporation exceeds rainfall and a wet pond would be unlikely to maintain the required permanent pool, the filtration system can be used. ADVANTAGES AND DISADVANTAGES Sand filters can be highly effective storm water best management practices. Sand filters achieve high removal rates for sediment, BOD, and fecal coliform bacteria. The filter media is periodically removed from the filter unit, thus also permanently removing trapped contaminants. Waste media from the filters does not appear to be toxic and is environmentally safe for landfill disposal. If they are designed with an impermeable basin liner, sand filters can also reduce the potential for groundwater contamination. Finally sand filters also generally require less land than other best management practices, such as ponds or wetlands. The size and characteristics of the drainage area, as well as the pollutant loading, will greatly influence the effectiveness of the sand filter system. For example, sand filters may be of limited value in some applications because of they are designed to handle runoff from relatively small drainage areas and they have low nutrient removal and metal removal capabilities. In these cases, other best management such as wet ponds, may be less costly and/or more effective. The system also requires routine maintenance to prevent sediment from clogging the filter. In some cases, filter media may need to be replaced 3 to 5 years. Lastly, sand filters generally do not control storm water flow, and consequently, they do not prevent downstream stream bank and channel erosion. Climatic conditions may also limit the filters performance. For example, it is not yet known how well sand filters will operate in colder climates or in freezing conditions excess flow. OPERATION AND MAINTENANCE All filter system designs must provide adequate access to the for inspection and maintenance. The sand filters should be inspected after all storm events to verify that they are working as intended. Sand filter systems can be deep, designated as confined spaces and require compliance with confined space entry safety procedures. Sand filters begin to experience clogging problems within 3 to 5 years. Accumulated trash, paper and debris should be removed from the sand filters every 6 months or as necessary to keep the filter clean. A record should be kept of the dewatering times for all sand filters to determine if maintenance is necessary. Corrective maintenance of the filtration chamber includes removal and replacement of the top layers of sand, gravel and/or filter fabric that has become clogged. The removed media may usually be disposed in a landfill. The City of tests their waste media before disposal. Results thus far indicate that the waste media is not toxic and can be safely land filled. Sand filter systems may also require the periodic removal of vegetative growth. Duel Media Filter In many cases, multiple types of media are layered within the filter. Typically, the layers (starting at the bottom of the filter and advancing upward) are garnet and sand. The picture below shows a cross-section through a dual media filter. The media in a dual or multi-media filter are arranged so that the water moves through media with progressively smaller pores. The largest particles are strained out by the sand. Then the sand and garnet trap the rest of the particulate matter though a combination of adhesion and straining. Since the particles in the water are filtered out at various depths in a dual or multi-media filter, the filter does not clog as quickly as if all of the particles were all caught by the top layer. The media in a dual or multi-media filter must have varying density as well as varying pore size so that they will sort back into the correct layering arrangement after backwashing. Garnet is a very dense sand which will settle quickly to the bottom of the filter. Activated Carbon Filter Activated carbon filtration is most effective in removing organic contaminants from water. Organic substances are composed of two basic elements, carbon and hydrogen. Because organic chemicals are often responsible for taste, odor, and color problems, activated carbon filtration can generally be used to improve aesthetically objectional water. Activated carbon filtration will also remove chlorine. Activated carbon filtration is recognized by the Water Quality Association as an acceptable method to maintain certain drinking water contaminants within the limits. Activated carbon filtration does remove some organic chemicals that can be harmful if present in quantities. The Safe Drinking Water Act mandates EPA to strictly regulate contaminants in community drinking water systems. As a result, organic chemical contamination of municipal drinking water is not likely to be a health problem. Contamination is more likely to go undetected and untreated in unregulated private water systems. AC filtration is a viable alternative to protect private drinking water systems from organic chemical contamination. Activated Carbon Filtration Process AC works by attracting and holding certain chemicals as water passes through it. AC is a highly porous material; therefore, it has an extremely high surface area for contaminant adsorption. The equivalent surface area of 1 pound of AC ranges from 60 to 150 acres. AC is made of tiny clusters of carbon atoms stacked upon one another. The carbon source is a variety of materials, such as peanut shells or coal. The raw carbon source is slowly heated in the absence of air to produce a high carbon material. The carbon is activated by passing oxidizing gases through the material at extremely high temperatures. The activation process produces the pores that result in such high adsorptive properties. The adsorption process depends on the following factors: 1) physical properties of the AC, such as pore size distribution and surface area; 2) the chemical nature of the carbon source, or the amount of oxygen and hydrogen associated with it; 3) chemical composition and concentration of the contaminant; 4) the temperature and pH of the water; and 5) the flow rate or time exposure of water to AC. Physical Properties Forces of physical attraction or adsorption of contaminants to the pore walls is the most important AC filtration process. The amount and distribution of pores play key roles in determining how well contaminants are filtered. The best filtration occurs when pores are barely large enough to admit the contaminant molecule. Because contaminants come in all different sizes, they are attracted differently depending on pore size of the filter. In general AC filters are most effective in removing contaminants that have relatively large molecules. Type of raw carbon material and its method of activation will affect types of contaminants that are adsorbed. This is largely due to the influence that raw material and activation have on pore size and distribution. Chemical Properties Processes other than physical attraction also affect AC filtration. The filter surface may actually interact chemically with organic molecules. Also electrical forces between the AC surface and some contaminants may result in adsorption or ion exchange. Adsorption, then, is also affected by the chemical nature of the adsorbing surface. The chemical properties of the adsorbing surface are determined to a large extent by the activation process. AC materials formed from different activation processes will have chemical properties that make them more or less attractive to various contaminants. For example chloroform is adsorbed best by AC that has the least amount of oxygen associated with the pore surfaces. The consumer can’t possibly determine the chemical nature of an AC filter. However, this does point out the fact that different types of AC filters will have varying levels of effectiveness in treating different chemicals. The manufacturer should be consulted to determine if their filter will adequately treat the consumer’s specific water problem. Contaminant Properties Large organic molecules are most effectively adsorbed by AC. A general rule of thumb is that similar materials tend to associate. Organic molecules and activated carbon are similar materials; therefore there is a stronger tendency for most organic chemicals to associate with the activated carbon in the filter rather than staying dissolved in a dissimilar material like water. Generally, the least soluble organic molecules are most strongly adsorbed. Often the smaller organic molecules are held the tightest, because they fit into the smaller pores. Concentration of organic contaminants can affect the adsorption process. A given AC filter may be more effective than another type of AC filter at low contaminant concentrations, but may be less effective than the other filter at high concentrations. This type of behavior has been observed with chloroform removal. The filter manufacturer should be consulted to determine how the filter will perform for specific chemicals at different levels of contamination. Iron And Manganese Contamination Sources, Adverse Effects and Control Methods The presence of iron and manganese in water causes serious commercial and health problems. Various treatment methods are available to treat water contaminated with these elements. However catalytic media is an excellent choice particularly. BIRM media is the most popularly used synthetically manufactured catalytic media. Iron and manganese are common metallic elements found in natures. Water percolating through soil and rocks dissolves iron and manganese, which then enters ground water supplies. In deep wells and springs, where both the oxygen content and PH tend to be low, water containing dissolved iron and manganese appears colourless. When the same water is exposed to air, these dissolved elements react with atmospheric oxygen and are converted to yellow coloured suspended particles, finally forming a reddish-brown residue that settles in water. Larger iron particles that do not settle remain suspended (colloidal iron) giving the water a reddish tint. Manganese usually dissolves in water, although some shallow wells contain colloidal manganese (black tint). These sediments and precipitates are responsible for the staining properties of water containing high concentrations of iron and manganese, which may be severe enough to plug water pipes. The following types of iron can be found in potable water supplies: • Sequestering Iron • Ferric Hydroxide or Red Water Iron • Ferrous Bicarbonate or Clear Water Iron As one can see, iron can be found in many different forms. This creates a problem for the removal of iron from water, since treatment methods differ for each type of iron.