Onsite Graywater Treatment in a Two-Stage Electro-Peroxone Reactor with a Partial Recycle of Treated Effluent

[Image: see text] The efficacy of an uncoupled electro-peroxone (E-peroxone) prototype reactor system for the treatment of synthetic graywater is determined. The two-stage E-peroxone process integrates ozonation with the in situ production of hydrogen peroxide (H(2)O(2)) in a first stage reactor before ozone (O(3)) is converted via the peroxone reaction to a hydroxyl radical ((•)OH). The two-stage prototype reactor system allows for the generation of H(2)O(2) via cathodic oxygen reduction in the first-stage reactor before mixing with O(3) in the second-stage reactor. This approach prevents the degradation of polytetrafluoroethylene (PTFE) coated carbon cathodes by (•)OH that takes place in a single well-mixed reactor that combines electrochemical peroxide generation with O(3). The dosage of H(2)O(2) into the second-stage reactor is optimized to enhance graywater treatment. Under these conditions, the uncoupled E-peroxone system is capable of treating synthetic graywater with an initial chemical oxygen demand (COD(0)) of 358 mg O(2)/L, a total organic carbon (TOC(0)) of 96.9 mg/L, a biochemical oxygen demand (BOD(0)) of 162 mg O(2)/L, and a turbidity of 11.2 NTU. The two-stage electro-peroxone system can reduce the initial COD(0) by 89%, the TOC(0) by 91%, BOD(0) by 86%, and the turbidity by 95% after 90 min of treatment. At this performance level, the reactor effluent is acceptable for discharge and for use in nonpotable applications such as toilet-water flushing. A portion of the effluent is recycled back into the first-stage reactor to minimize water consumption. Recycling can be repeated consecutively for four or more cycles, although the time required to achieve the desired H(2)O(2) concentration increased slightly from one cycle to another. The two-stage E-peroxone system is shown to be potentially useful for onsite or decentralized graywater treatment suitable for arid water-sensitive areas.