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 16.d. The variations of oxidation reduction potential ( E _h) and pH were continuously monitored during the A/A digestion and the conversions of ammonium and nitrate were investigated. Important features on both E _hand pH profiles were identified to develop process control strategy. Since the feature point on E _hprofile where d ² E _h/d t ²0 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/d t0. A real-time control strategy of A/A digestion of sludge was developed and tested with pH and E _has 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(7.75.d for a 20.d period).