Enhanced Treatment of Wastewater Effluent with Ozonation for Micropollutant Abatement: Feasibility and Process Optimization

Abstract

Numerous chemicals in modern society are released into sewage and flow into the surface water and become organic micropollutants (OMPs). Some OMPs negatively affect the aquatic ecosystem and drinking water quality. Since OMPs are not entirely removed in conventional wastewater treatment, enhanced treatment of wastewater effluent has been considered for the OMP removal. Oxidative water treatment such as ozonation has been widely used in drinking water treatment for chemical oxidation and disinfection. As the process efficiency of ozonation is significantly affected by water matrix components, feasibility assessment and optimization are required for successful ozone application to enhanced wastewater treatment. This thesis aims to evaluate the feasibility of ozonation as an enhanced wastewater treatment option in South Korea and to optimize the ozonation conditions. For this, twelve wastewater treatment plants (WWTPs) in Korea were assessed for the ozone applicability by considering the oxidation efficiency of OMPs, toxic byproduct formation, and toxicity change. Ozonation was feasible to most WWTPs in terms of the oxidant stability and bromate formation, while high levels of N-nitrosodimethylamine (NDMA) were formed in some WWTPs. Moreover, ozone alone and ozone with hydrogen peroxide (Peroxone) were compared in oxidation efficiency of OMPs, microbial inactivation, and toxic byproduct formation. The Peroxone process showed less bromate formation and similar OMP elimination efficiency than the ozone while decreased microbial inactivation efficiency, indicating that the trade-off between disinfection vs bromate formation should be considered. Pre-chlorination was also investigated as an option to remove N,N-dimethylhydrazines, potent NDMA precursors. Chlorination effectively removed N,N-dimethylhydrazines and their NDMA formation potential during ozonation without forming NDMA. Overall, the feasibility evaluation of ozonation provides information on ozonation suitability as well as optimized ozonation to WWTPs. Optimized processes should be selected and designed in consideration of the water quality components of wastewater effluents and the expected treatment effects. Moreover, newfound byproducts and toxicity changes during ozonation should also be considered for the application of optimized ozonations to WWTPs.