Bench-Scale Digestion Studies

Four, 1-L bench-scale digesters were operated for 25 days 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. Two of the digesters were sparged with air and the remaining two digesters were 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 volatile suspended solids (VSS) reduction was determined and average first order degradation constants (K_D) for the aerobic and ozonated digesters were 0.0824 days^–1 and 0.108 days^–1 respectively, indicating that ozone was more effective at destroying VSS than oxygen. Total chemical oxygen demand (COD) removals averaged 37% and 64%, respectively for the aerobic versus ozonated digesters. Soluble COD (SCOD) concentrations in the digesters increased from 0 to 15.5 mg/L in the aerobic digesters and from 0 to 293.5 mg/L in the ozonated digesters due to solubilization of the biological sludge solids. Approximately 1.82 mg of oxygen was required per mg of total volatile solids (TVS) destroyed. Average ozone dosages observed in this study were 2.6 and 2.8 mg of O₃ per mg of total solids (TS) destroyed for ozonated digesters 1 and 2, respectively.