Bench-scale ozonation study of waste activated sludge

Abstract

A bench-scale ozonation study was conducted on waste activated sludge (WAS) in a 10-L, clear PVC, semi-batch, bubble column reactor. Two separate runs were performed on 5-L samples of WAS obtained from the Rocky Creek Wastewater Treatment Plant (WWTP) in Macon, Georgia. The Rocky Creek facility uses the extended aeration activated sludge process to treat domestic wastewater. Ozone was sparged through a porous diffuser at an application rate of 0.0525 mg O3 min− 1 at contact times of 9 days and 12 days, respectively, during Runs #1 and #2. Parameters that were monitored during the study included: alkalinity, ammonia, conductivity, nitrite, nitrate, pH, phosphate, solids degradation rate coefficient (KD), soluble chemical oxygen demand (SCOD), total chemical oxygen demand (TCOD), total dissolved solids (TDS), total solids (TS), total volatile solids (TVS), turbidity, and unstirred sludge volume index (SVIu). Ozone was very effective at removing TCOD and TS. TCOD removals were 43% and 99% respectively for Runs #1 and #2. Total solids removal during Runs #1 and #2 was 50% and 95%, respectively. The degradation rate coefficient (KD) based on VSS was 0.17 days− 1 and 0.54 days− 1 for Runs #1 and #2. Both the nitrate and phosphate concentrations increased as ozone contact time increased during each run. The unstirred SVI decreased with an increase in ozone contact time, however, extended ozonation caused the SVI to increase. Actual ozone dosages for Runs #1 and #2 were 0.0036 and 0.011 mg O3 per mg TS removed.