Influence of sludge retention time on phosphorus removal fficiency in an anaerobic - oxic bioreactor

Abstract

Sludge retention time (SRT) is an operational important parameter for biological phosphorus (TP) removal. This study was carried out to examine the influence of SRT (varied from 5 to 20 days) on TP removal efficiency in an anaerobic-oxic bioreactor. The obtained results showed that the food/microorganism ratio was reduced (from 0.58 to 0.29 mg COD/mg MLVSS/d) when SRT was increased. The mixed liquor suspended solids (MLSS) and mixed-liquor volatile suspended solids (MLVSS) were both increased when SRT was increased. However, the ratio of MLVSS/MLSS was reduced from 83.9% down to 76.2%. When SRT was increased the TP content in sludge was increased from 3.82% to 6.09%. SRT increased from 5 to 10 days resulted in TP removal efficiency increasing from 77.3% to 87.8%. However, TP removal efficiency was decreased from 87.8% to 81.2%, when SRT was increased from 10 to 20 days respectively. Themore SRT was increased the more total nitrogen removal was achieved. SRT almost did not affect the process of organic removal.