FERMENTATION OF RAW SLUDGE AND ELUTRIATION OF RESULTANT FATTY-ACIDS TO PROMOTE EXCESS BIOLOGICAL PHOSPHORUS REMOVAL

Research in South Africa has highlighted the dependence of biological phosphate removal mechanisms on the presence of certain minimum concentrations of some readily biodegradable materials including inter alia volatile fatty acids. Generation of these compounds was achieved on an experimental basis at the Johannesburg Northern Works by the fermentation of primary sludge either in primary settling tanks or off-line in high rate "acid" digesters. Elutriation of the volatile fatty acids from the sludge was achieved by recycling the sludge to the influent sewage stream. Significant improvements in phosphate removal were observed and it was decided to design primary sludge treatment facilities to specifically generate the volatile fatty acids. This paper describes the design philosophy adopted and discusses the preliminary results obtained from the recently commissioned plant at the Johannesburg Northern Works and Bushkoppie plants.