Real-time control of aerobic/anoxic digestion for waste activated sludge

Experiments were conducted to study the performance characters of aerobic/anoxic(A/A)digestion of sludge at 30±1℃,while the sludge retention time(SRT)was kept 16d.The variations of oxidation reduction potential(Eh)and pH were continuously monitored during the A/A digestion and the conversions of ammonium and nitrate were investigated.Important features on both Eh and pH profiles were identified to develop process control strategy.Since the feature point on Eh profile where d2 Eh /dt2=0 is very stable during anoxic cycle,it can be used to determine the end of denitrification.The end of nitrification can be identified according to dpH/dt=0.A real-time control strategy of A/A digestion of sludge was developed and tested with pH and Eh as control parameters.It is shown that the performance of the real-time control strategy is better than that of a fixed-time control strategy.While the real-time controlled A/A digestion system can achieve a similar volatile suspended solids(VSS)destruction efficiency of 35.2% as a continuously aerated system,it improves the supernatant quality in a shorter aeration time(7.75d for a 20d period).