Submerged Aerated Filters is designed to reduce the amount of BOD and ammonia nitrogen in settled sewage and industrial effluents. Aerated effluent is made to flow through submerged media, which acts as a physical support for the growth of micro organisms. The media may be high void age corrugated cross flow PVC, coarse sand, expanded shale, pozzolanic material, buoyant plastic or graded blast furnace slag. These filters can be seeded with bacterial cultures to accelerate start-up.