Effect of sludge retention time and phosphorus to carbon ratio on biological phosphorus removal in HS-SBR process

Sludge retention time (SRT) and phosphorus to carbon ratio (P/C) in the feed are important control parameters in biological phosphorus removal. In this study, humus soil sequencing batch reactor (HS-SBR) process was operated with different SRTs (five, 10 and 15 days) and P/C feeding (0.0125 and 0.1) to evaluate their phosphorus removal efficiencies. The HS-SBR was composed of a humus soil reactor (HSR) and a conventional SBR (designated as hsSBR to differentiate from the conventional SBR used as a control). The results showed that the phosphorus removal efficiency was 82.7%, 97.3% and 97.3% at SRTs of five, 10 and 15 days respectively and acetate utilization efficiency for phosphorus release with SRTs of 10 and 15 days was much higher than that with an SRT of five days. In addition, a high P/C feeding (0.1) could promote the growth of the phosphate accumulating organisms in the hsSBR; however, the efficiency of phosphorus removal was lower than a low P/C feeding (0.0125) at an SRT of 15 days. All these observations suggested that a relatively long SRT and low P/C feeding exert a useful effect on the phosphorus removal in the hsSBR.