[Feasibility study for limited filamentous bulking under low dissolved oxygen at different operation regimes]

Limited filamentous bulking under low dissolved oxygen (DO) is a new technology for energy saving and high quality effluent. In order to investigate the feasibility of this technology, four sequence batch reactors (SBRs) were occupied to operate at different regimes to stimulate different processes under low DO (0.5 mg/L). Sludge settleability, floc structure, pollutant removal and aerated energy consumption were investigated. The results showed that limited filamentous bulking under low DO was hard to realize in the single-stage aerobic reactors for they were prone to bulking severely, while it could be achieved stably in the pre-denitrification reactors when the feed length was between 60 and 90 minutes. Compared with normal sludge at the same DO, limited filamentous bulking sludge acquired by low DO displayed its high energy-saving effect. In addition, the specific ammonia consumption rate of limited filamentous bulking sludge was about 2 times higher than the one of normal sludge. On the contrary, the total nitrogen removal efficiency was lower. Further analysis indicated that stable limited sludge bulking could be achieved in a good alternative anoxic/anaerobic/aerobic condition without too high organic loading.