A process in which settled sewage uniformly trickles downward through a bed of inert material such as slag, moulded plastics or clinker, thus permitting contact with the biological film with which the surfaces of the medium are coated so that oxidation and clarification take place.

The natural process of beneficial bacteria breaking down harmful ammonia to nitrite and then converting nitrite to less toxic nitrate.

The process of filtering water through a filter medium that has been allowed to develop a microbial biofilm that assists in the removal of fine particulate matter and dissolved organic materials. Also [..]