Water filtration is a physical process of separating suspended and colloidal particles from waste by passing the water through a granular material. The process of filtration involves straining, settling, and adsorption. As floc passes into the filter, the spaces between the filter grains become clogged, reducing this opening and increasing removal. Some material is removed merely because it settles on a media grain. One of the most important processes is adsorption of the floc onto the surface of individual filter grains. In addition to removing silt and sediment, flock, algae, insect larvae, and any other large elements, filtration also contributes to the removal of bacteria and protozoans such as Giardia lamblia and Cryptosporidium . Some filtration processes are also used for iron and manganese removal.
The surface water treatment rule (SWTR) specifies four filtration technologies, although SWTR also allows the use of alternate filtration technologies (e.g., cartridge filters). These include slow sand filtration see Figure, rapid sand filtration, pressure filtration, diatomaceous earth filtration, and direct filtration. Of these, all but rapid sand filtration is commonly employed in small water systems that use filtration. Each type of filtration system has advantages and disadvantages. Regardless of the type of filter, however, filtration involves the processes of straining (where particles are captured in the small spaces between filter media grains), sedimentation (where the particles land on top of the grains and stay there), and adsorption (where a chemical attraction occurs between the particles and the surface of the media grains).
FLOW RATE THROUGH A FILTER (gpm)
Flow rate in gpm through a filter can be determined by simply converting the gpd flow rate indicated on the flow meter. The flow rate (gpm) can be calculated by taking the meter flow rate (gpd) and dividing by 1440 min/day, as shown in Equation.
Flow rate gpm=flow rate (gpd) / 1440 min/day
- gpm:gallon per minute
- gpd:gallon per day