Upgrade of the biggest catalytic ozonation wastewater treatment plant in China: From pollution control to carbon reduction.

Catalytic ozonation is a widely used effective technology in advanced treatment for the removal of refractory organics from wastewater. However, it is also a highly energy-consuming technology, usually accounting for 30%∼40% of the total electricity consumption of a wastewater treatment plant (WWTP). The O consumption per unit of COD removed (g-O/g-COD) is usually higher than 1.5 g-O/g-COD, and the total carbon emission from catalytic ozonation is usually higher than 393.12 kgCO e/m of wastewater. In this study, we investigated an energy reduction strategy for the biggest catalytic ozonation WWTP, from laboratory-scale experimentation to corresponding engineering application. Laboratory-scale experiments showed that the mass transfer rate of dissolved O to the catalyst surface is crucial for COD removal efficiency. To improve the efficiency of catalytic ozonation, adding effluent backflow is a simple method that can enhance the removal of extracellular polymeric substances (EPS) from the catalyst surface and promote surface exposure. In the pilot-scale experiment (48 m/d), when the backflow ratio increased from 0% to 100% (the optimal value), the proteins in EPS on the catalyst surface decreased significantly by 66.7%. The corresponding O consumption per unit of COD removed was reduced from 2.0 to 1.0 g-O/g-COD. Furthermore, in the engineering application (52,000 m/d) with a backflow ratio of 100%, the average effluent COD reduced from 52.0 to 43.3 mg/L, and the O consumption per unit of COD removed decreased from 0.98 to 0.69 g-O/g-COD. In terms of carbon reduction, the indirect carbon emission reduction was approximately 3.0 × 10 t CO e/a. This study demonstrates the advantages of catalytic ozonation improvement and provides an engineering model of energy conversation and carbon emission reduction for over 35 similar WWTPs in China.