A sludge characterization assay for aerobic and denitrifying phosphorus removing sludge

It was recently recognized that denitrifying bacteria, as well as aerobic bacteria, contribute to the biological phosphorus removal process. For evaluation of the phosphorus removal process it is necessary to have tests enabling a proper characterization of the microbial population in the activated sludge. In this study we evaluated the possibility of anoxic phosphorus release or aerobic/anoxic phosphorus uptake tests for sludge characterization. Hereto we employed sludge mixtures of enrichment cultures from laboratory sequencing batch reactor (SBR) systems operated under aanaerobic-aerobic (A/O) or anaerobic-anoxic (A2) conditions. It is shown that interpretation of phosphorus release tests, with or without nitrate present, is difficult. On the other hand a comparison of phosphorus uptake under aerobic and anoxic conditions leads to a straightforward characterization of the microbial population in the phosphorus removing organisms, with respect to their phosphorus removal activity under aerobic and anoxic conditions.