Optimization of Ozonation Pretreatment Combined with Aerobic Biological Treatment for Enhanced Removal of Organic Pollutants in Industrial Wastewater

Industrial wastewater from organic acid production contains a complex mixture of biodegradable and recalcitrant organic compounds, making treatment challenging. This study investigated the role of ozone pretreatment at various power levels (600–800 W) and contact times (40–120 min) prior to aerobic biological treatment. The wastewater was adjusted to neutral pH before ozonation to ensure stability and to simulate practical operating conditions. Ozonation effectively reduced COD and BOD, while also altering the BOD/COD ratio, a key indicator of biodegradability. Moderate ozonation (600 W, 80 min) increased the BOD/COD ratio to ~ 0.38, indicating improved biodegradability and facilitating faster microbial degradation. In contrast, excessive ozonation (800 W–120 min) lowered the BOD/COD ratio (~0.16), suggesting reduced biodegradability despite greater initial organic removal. Energy analysis further confirmed that 600 W for 80 min provided the most favorable balance, with an EEO of 161 kWh·m−3·order−1. In contrast, longer contact times or higher power levels only marginally improved COD removal but significantly increased energy demand. These findings emphasize the trade-off between reducing overall organic load and preserving biodegradability, highlighting that carefully optimized ozonation not only lowers pollutant levels but also enhances the effectiveness of subsequent biological treatment. The insights gained provide practical guidance for designing sustainable hybrid ozonation–biological treatment strategies for industrial effluents.