Abstract
Polyphosphate-accumulating organisms (PAOs) indicators in enhanced biological phosphorus removal (EBPR) process evaluated by conventional analyses and that by microautoradiography- fluorescence in situ hybridization (MAR-FISH) analysis were compared and discussed. Two types of activated sludge, EBPR sludge and non-EBPR sludge, were mixed in the different ratios and operated in the acetate-fed sequencing batch reactors (SBRs). During the start-up phase, three conventional indicators, the phosphorus content in biomass, the population density of Rhodocyclus-related PAO (RPAO) and the anaerobic phosphorus release, were analyzed. The increase of the population density of RPAO and the phosphorus content exhibited different behavior. This difference might be derived from the change in physiology of RPAO. The anaerobic phosphorus release also showed different result from the other two indicators. It might result from the low acetate assimilation activity of PAOs and from the acetate assimilation by other bacteria. Both the acetate assimilation by α-Proteobacterial G-bacteria and no acetate assimilation by some RPAO were visualized by MAR-FISH analysis whereas the acetate assimilation by most of RPAO was also visualized. Conventional indicators evaluated in this study gave the different results because 1) each indicator is based on each activity of PAOs, such as acetate assimilation, phosphorus uptake and growth activity, and 2) the activities of other organisms should affect each indicator. MAR-FISH analysis is more appropriate for the determination of the actual substrate uptake activities, but the further identification of their phylogenetic affiliation and the determination of the biochemistry of PAOs and glycogen-accumulating organisms (GAOs)/G-bacteria are also still needed.
