Fine particulate matter that escapes the sedimentation process is removed by the filtration process. In addition to trapping solids, the filters provide the capacity to remove dissolved organic compounds through the process of biological degradation.
The plant is equipped with 12 filters, each consisting of a large concrete box containing four feet of biologically active carbon over sand and gravel. Water quality is continuously monitored to meet turbidity standards.
The filters must be periodically backwashed, or cleaned, by reversing the direction of water. During the backwash cycle, compressed air followed by clean water is forced backwards through the filter bed, thereby removing the particles that have been trapped in the media. The backwash water with the removed particles is sent to the residual solids processing facility.