| Title |
Alternative Aerobic - Anoxic Sludge Digestion with pH Control |
| Abstract |
The results have established pH as a viable process control parameter for the AAA (Alternative Aerobic-Anoxic) process. During the course of aerobic-anoxic alternation, important features appear on both the ORP and pH profiles. Newly identified pH features applicable to the AAA process control include the ammonia valley, a well defined point for terminating aerobic cycles, and the nitrate apex which can be used to terminate anoxic cycles and initiate aerobic cycles. Such feature provide valuable insights into the respiratory state of the system, which is constantly changing between nitrification and denitrification. The reproducibility of the ORP and pH curves enables the use of these features to determine the aerobic and anoxic periods in the AAA process on a real-time basis. In addition, it has been shown that pH control processes certain advantages over ORP control. Two real-time AAA control strategies, namely fixed pH set points and dynamic pH variation, were briefly presented and discussed. Both strategies were found to be feasible for the real-time control of the AAA process. Results from labortory scale AAA sludge digestion using fixed pH set points(6-8) indicated that 36% MLVSS reduction, 39% TN reduction and almost 48% saving in aeration energy was achieved after 300 hrs of digestion. |