ABSTRACT
The filtration process involves wastewater being passed through a filter media of sand, anthracite, or a layer of each to remove suspended and/or colloidal material.
Filtration is used as a form of tertiary treatment following secondary biological treatment or after physical chemical treatment (coagulation/flocculation/sedimentation).
Filtration effectively reduces turbidity and improves chlorine disinfection by reducing chlorine demand.
Filtration may be provided by open, gravity filters or in enclosed, pressure filters.
Wastewater is passed downward through the filter media. With time, the filter media becomes plugged with material removed from the wastewater and must be cleaned by reversing the flow (backwashing). This upward backwash flow rate must be sufficient to fluidize the media particles, scrub and resuspend the collected particles, and wash them from the bed. The backwash wastewaters are usually recycled back to the head of the plant.
