USE OF PH AS CONTROL PARAMETER FOR AEROBIC ANOXIC SLUDGE-DIGESTION/

Alternating aerobic/anoxic (A/A) digestion of waste activated sludge o ffers many advantages over traditional (aerobic or anaerobic digestion ) methods. However, one of the main concerns in AIA digestion is the d evelopment of an on-line control strategy for alternating aerobic and anoxic cycles. Computerized pH monitoring has revealed two well-define d control points that correspond to complete nitrification (ammonia va lley) and denitrification (nitrate apex). The pH control points were c onsistent with those previously identified using the oxidation reducti on potential. Based on these findings, two real-time control strategie s were developed and tested. First, pH was allowed to increase (anoxic ) and decrease (aerobic) within preset limits to control A/A cycling. A second approach detected the points of complete nitrification and de nitrification using the differential of the pH signal. Comparison of t he A/A digestion results with aerobic digesters indicated similar mixe d-liquor volatile suspended solids and fecal coliform destruction with aerobic digestion but with better total nitrogen removal and superior dewatering characteristics.