Onsite Graywater Treatment By Decoupled Electro-Peroxone Process with Recycled Effluent

Abstract

This study investigates the efficacy of a decoupled electro-peroxone (E-peroxone) process for the lab-scale treatment of synthetic graywater. The E-peroxone process generally integrates conventional ozonation with in situ production of hydrogen peroxide (H2O2) in a single reactor for the transformation of ozone (O3) to hydroxyl radicals (*OH). In this study, however, the electrolysis of H2O2 generation via cathodic oxygen reduction was performed separately in order to finely control the H2O2 utilization for the E-peroxone process and to prevent the degradation of polytetrafluoroethylene (PTFE) coated carbon cathodes by highly reactive *OH. The dosage of the electro-generated H2O2 into a main reactor was optimized to enhance the performance of synthetic graywater treatment by facilitating the *OH formation. Under the optimal condition, the decoupled E-peroxone system treated synthetic graywater with initial chemical oxygen demand (COD) of 358 mg O2/L, total organic carbon (TOC) of 96.9 ppm, biochemical oxygen demand (BOD) of 162 mg O2/L, and turbidity of 11.2 NTU; the system consistently achieved removal of 89% COD, 86% TOC, 91% BOD, and 95% turbidity after 90-minute treatment, producing an effluent acceptable for discharge and non-potable applications such as toilet flushing. Part of the effluent was also recycled back into the system for H2O2 generation to minimize water consumption. This recycling process was successfully repeated consecutively for four cycles. Although the duration to reach the desirable concentration of H2O2 slightly increased from cycle to cycle, the system maintained comparable treatment performance with COD and TOC removal above 85% and 73%, respectively. Given these promising results in single-pass treatment and closed-loop recycling of graywater, the decoupled E-peroxone system can provide effective decentralized wastewater treatment for remote or water-sensitive areas. Figure 1