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

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.