ABSTRACT
A precise defi nition of secondary treatment is given by the Chartered Institution of Water and Environmental Management (IWEM) as:
the treatment of sewage, usually after the removal of suspended solids, by bacteria under aerobic conditions during which organic matter in solution is oxidized or incorporated into cells which may be removed by settlement. This may be achieved by biological fi ltration or by the activated sludge process. Sometimes termed aerobic biological treatment. ( IWEM, 1992 )
The Municipal Wastewater Treatment Directive (Section 8.3) defi nes secondary treatment more broadly as ‘ treatment of municipal wastewater by a process involving biological treatment with a secondary settlement ’ . So secondary treatment is a biological process where settled sewage enters a specially designed reactor where under aerobic conditions any remaining organic matter is utilized by micro-organisms.
