Effect of operating conditions on biological phosphorus removal

Abstract

Biological phosphorus‐removal processes incorporate a sequence of anaerobic and aerobic contact tanks to select for phosphorus‐storing bacteria and provide them with necessary substrates. Acetate consumption and phosphorus release during anaerobic contacting is followed by phosphorus uptake and storage during aerobic contacting. Bench‐scale studies were conducted in this research to examine the transient effects of longer anaerobic contact time, longer aerobic contact time, and decreased influent chemical oxygen demand (COD) feed concentration on phosphorus release, phosphorus uptake rate, and net phosphorus removal in a sequencing batch reactor (SBR) system enriched for biological phosphorus removal. Batch tests were also performed with sludge from a continuous‐flow anaerobic–anoxic–aerobic biological phosphorus‐removal system to determine the effect of increased anaerobic contact time on phosphorus release and uptake. Both systems were fed a complex synthetic feed, but the SBR system was fed only acetate as its carbon source during the transient effects study. During steady‐state operation of the SBR, the ratio of acetate COD consumed to phosphorus removed averaged 16.5:1, and the molar ratio of acetate used to phosphorus released in the anaerobic period was 0.75:1. In all cases when anaerobic contacting occurred without acetate consumption, phosphorus release rates were lower than normal. Only 40 to 60% of the phosphorus released under acetate‐deficient conditions was taken up under subsequent aeration. Transient effects of longer aeration time and lower influent feed acetate concentration in the SBR experiments resulted in lower phosphorus release and a significant decrease in phosphorus‐removal efficiency in the SBR cycle following the transient change.