Multi-Media Gravity Filters

Filtration is a physical process where the organic and inorganic suspended solids left in the process are removed. The filter consists of six filter cells each with a 4-foot bed of media consisting of anthracite coal, silica sand, ilmenite sand, and different sizes and densities of gravel.

As the wastewater passes through the filter media, suspended solids are filtered out. As the filter run progresses, the available pore space in the media decreases as more solids are trapped. When the pressure loss through the bed becomes excessive, the filters must be cleaned by backwashing. All six filters are backwashed on a daily basis. The filters are backwashed using our final effluent water at a flow rate of approximately 8,000 gallons per minute. This slowly lifts the filter media flushing out the trapped solids which are then discharged to the backwash storage tank as spent backwash water. From the backwash storage tank the spent backwash wastewater gets pumped to the sludge thickeners as dilution water. The spent backwash water can also be sent to the process drain and ultimately pumped back to the head end of the plant.