The use of simultaneous chemical precipitation in modified activated sludge systems exhibiting biological excess phosphate removal Part 1: Literature review

Abstract

Simultaneous chemical precipitation of phosphate (P) is commonly used in activated sludge systems to supplement biological excess P removal (BEPR). This paper briefly reviews the use of metal salts (typically iron or aluminium) for this purpose and focuses on the question of possible interference with the BEPR mechanism arising from the addition of chemical precipitant. Some evidence of weakened BEPR has emerged in activated sludge systems in South Africa, based partly on observations from full-scale plants in which controlled studies were not satisfactorily carried out. In some cases, extrapolations have been made either from laboratoryscale systems in which unrealistically large doses of metal precipitant were used, or from systems which were not operated close to steady-state conditions over extended periods. In other cases where simultaneous precipitation has been applied, the systems studied were not designed for BEPR. It was concluded that there is room for further investigation of the reported negative effect of simultaneous chemical precipitation on BEPR.

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