Effects of Ozone Dose and Contact Time on Ozonation Process Performance for Treatment of High Rate Activated Sludge Process Effluent

In recent years, there has been an increase in the interest on organic compounds originating from anthropogenic activities. The presence of these micropollutants in waterbodies can be detrimental for the aquatic organisms even at their trace concentrations. Removal of micropollutants from wastewater by conventional treatment methods is quite limited, thereby existing wastewater treatment plants are not capable of removing these micropollutants. This study investigated the removal of 27 micropollutants and conventional pollution parameters by ozonation of the effluent from a pilot-scale high-rate activated sludge system treating municipal wastewater. Different ozone dosages and contact times were tested during the study. Results revealed that 7 out of 27 micropollutants were detected in the effluent. Over 45% chemical oxygen demand (COD) removal and over 65% total suspended solids (TSS) removal were achieved by the ozonation process. Among the various ozone dosage and contact time combinations investigated in the study; 6 mg/L ozone dosage-20 min contact time, and 9 mg/L ozone dosage-10 min contact time alternatives resulted with the best treatment performance in terms of the removal of micropollutants, COD, TSS, and turbidity. A feasibility analysis was conducted to evaluate the best operational conditions from a techno-economic perspective and the results revealed that the unit cost for ozonation process ranged between 0.033 $/m³ and 0.043 $/m³. Additionally, considering the feasibility, 6 mg/L ozone dose–20 min contact time combination was found as the optimum alternative. Based on the promising results obtained in this study, ozonation can be offered as a polishing step for the effluents of high-rate activated sludge systems for the improving of the effluent quality.