Parallel Bench-Scale Digestion Studies

Two, 2-L bench-scale digesters were operated for 30 days in Phase I and 32 days in Phase II to evaluate the effectiveness of oxygen and ozone on sludge stabilization. Each digester contained waste activated sludge generated from the Rocky Creek Wastewater Treatment Plant (WWTP) in Macon, Georgia. One digester was sparged with air and the other digester was sparged with ozone. The following parameters were measured frequently during the bench-scale study: pH, total and soluble chemical oxygen demand (COD), temperature, total and volatile solids, and total suspended and volatile suspended solids. The kinetics of total solids (TS) reduction was determined and first order degradation coefficients (K_D) for the aerobic and ozonated digesters were 0.0073 days^–1 and 0.0278 days^–1 respectively in Phase I and 0.0049 days^–1 and 0.0186 days^–1 in Phase II; indicating that ozone was more effective at destroying TS than oxygen. Total chemical oxygen demand (COD) removals averaged 34.8% and 57.5% respectively, for the aerobic versus ozonated digesters. Soluble COD (SCOD) production per gram of total solids (TS) destroyed was 9.5 and 4.2 respectively, for the Phase I and Phase II aerobic digester and 146 and 120 respectively, for the Phase I and Phase II ozonated digester. Approximately 1.89 mg of oxygen equivalents in terms of COD was required per mg of total volatile solids (TVS) destroyed in the aerobic digester in Phase I versus 1.96 mg oxygen equivalents per mg TVS destroyed in Phase II. Average ozone dosages observed in this study were 2.6 and 0.57 mg of O₃ per mg of total solids (TS) destroyed for ozonated digesters in Phase I and II, respectively.