In Situ Microscale Analyses of Activated Sludge Flocs in the Enhanced Biological Phosphate Removal Process by the Use of Microelectrodes and Fluorescent In Situ Hybridization

Abstract

Phosphate concentration microprofiles were measured within activated sludge flocs in the enhanced biological phosphate removal EBPR process, and a fluorescent in situ hybridization and clone library analysis were conducted to indentify polyphosphate accumulating organisms PAOs. The center of the flocs had the highest phosphate concentrations, and the stratification of the flocs found by microprofiling indicated that the PAOs were probably distributed evenly throughout the flocs. Under the assumption that the phosphate, which was generated because of phosphate release by microbial activity, was not consumed by microbes and was only transferred from the flocs to the bulk by diffusion during anaerobic conditions, the effective diffusion coefficient Df for phosphate release within the flocs was calculated to be 3.3310 7 cm 2 /s at the end of the anaerobic phase of the EBPR process. These results provide a better under- standing of the phosphate removal mechanism, and this understanding of the internal function of flocs can lead to improvement in the modeling, design, and operation of the biological phosphorus removal process.