Full Scale Phosphate Removal Experiences in the Umhlatuzana Works at Different Sludge Ages

Abstract

This paper describes full-scale phosphate removal at 69, 38 and 8 day sludge ages. The results of operation at 20 days are also mentioned, but were not monitored intensively. Exceptionally good results were obtained treating an unsettled domestic wastewater in a simple activated sludge plant, under optimum operating conditions in a soft water region. At sludge ages of 69 and 38 days, more than 92% of the influent carbon, nitrogen and phosphorus were removed simultaneously and consistently without chemical addition or tertiary treatment. The Authors attribute the extra-ordinarily high efficiency of phosphate removal to the functioning of two mechanisms which complement one another. There is sufficient practical evidence to suggest that the low concentration of residual phosphate is governed by the equilibrium kinetics of a solid phosphate phase and not by micro-organisms. Major findings have been that restricted oxygen input is associated with efficient phosphate removal and that it is possible to condition activated sludge anaerobically so that its behaviour changes gradually from the anaerobic phosphate release regime associated with luxury uptake by Acinetobacter to a regime of insignificant phosphate release associated with the most efficient phosphate removal.