Study on specific strategies of controlling or preventing sludge bulking in S2EBPR process

Side-stream enhanced biological phosphorus removal (S2EBPR) process was regarded as a promising innovative modification and emerging alternative to EBPR configurations, and more attention should also be paid to controlling and preventing sludge bulking. In this study, a pair of lab-scale continuous flow anaerobic-anoxic-aerobic (A(2)/O) and S2EBPR reactors were synchronously started and operated for 150 days. After 54 days of adjustment and maintenance, the reactors were successfully started. However, considering that the sludge bulking problem in the reactors occurred successively, the desired phosphorus removal performance were not secured. The causes of the sludge bulking in A(2)/O and S2EBPR reactors were investigated by comparing the performance and stability, ex situ EBPR metabolic activity, extracellular polymeric substances (EPS), sludge settling characteristics, and microbial community under different operating conditions. The results of the experiment indicated that, under the same conditions (including influent characteristics, environmental and operational conditions, etc.), the stability of the system in regards to sludge bulking was ranked in the following order: side-stream ratio of 6.7 % S2EBPR > side-stream ratio of 10.0 % S2EBPR > A(2)/O > side-stream ratio of 13.3 % S2EBPR. The study of sludge bulking in the continuous flow reactors demonstrated that the side-stream ratio adjustment of S2EBPR could be used as an effective strategy to control or prevent sludge bulking.