Filtration
Filtration is the process of reducing water turbidity after it has passed through the stage of coagulation and flocculation. The filtration step removes the floc and precipitates that have formed in addition any other microorganisms that are present. The water is passed through a filter to remove these impurities. As particles pass through the filter, they adsorb (stick) to the filter medium.
Types of Filters
Gravity Filters
Gravity filters rely on gravity to pass the water through the filter media. Common media include sand, granular activated carbon, and anthracite coal. In many cases, a combination of materials are employed in the filter (EPA, 2013).
Types of Gravity Filters:
slow sand
rapid sand
high rate
deep bed, monomedium
Gravity filters rely on gravity to pass the water through the filter media. Common media include sand, granular activated carbon, and anthracite coal. In many cases, a combination of materials are employed in the filter (EPA, 2013).
Types of Gravity Filters:
slow sand
rapid sand
high rate
deep bed, monomedium
Pressure Filters
Pressure filters are similar to gravity filters, but instead of gravity they use a pump or high pressure water source to force water through a steel column that contains the filter. Sand and activated carbon are often used as the filtration media (EPA, 2013).
Pressure filters are similar to gravity filters, but instead of gravity they use a pump or high pressure water source to force water through a steel column that contains the filter. Sand and activated carbon are often used as the filtration media (EPA, 2013).
Backwash
During the filtration process, the spaces between the sand and other filtration media becomes clogged with floc, reducing the efficiency of the filter. In order to remove the particles and clean the media, the water is reversed back over the filter with increased velocity, dislodging the material (EPA, 2013).
During the filtration process, the spaces between the sand and other filtration media becomes clogged with floc, reducing the efficiency of the filter. In order to remove the particles and clean the media, the water is reversed back over the filter with increased velocity, dislodging the material (EPA, 2013).