Denitrification behaviour in biological excess phosphorus removal activated sludge systems

A literature review of denitrification behaviour in biological excess phosphorus removal (BEPR) activated sludge systems was performed. Wentzel et al. (1989a,b) (Wat. S.A. 15, 71-88; Wat. S.A. 15, 89-102) excluded denitrification by polyP organisms in modelling the BEPR process as observations indicated that minimal denitrification ocurred in laboratory systems comprised mainly of polyP organisms. In contrast, results of microbiological studies and many continuous and batch reactor experimental studies reviewed here indicate that a significant fraction of the polyP organisms can use nitrate as an electron acceptor in the absence of oxygen for oxidation of stored PHB and simultaneous uptake of phosphorus. Quantifying the extent of denitrification by polyP organisms in a particular system requires further information on factors determining the fraction of organisms capable of denitrification and the stoichiometry of the process.