Insight into the dual-cathode peroxi-coagulation process for cost-effective treatment of organic wastewater: Increase pH application range and reduce iron sludge

Abstract

An improved dual-cathode peroxi-coagulation (PC) process using natural air diffusion electrode (NADE) and HNO3 modified carbon felt (MCF) was first proposed to improve the removal efficiency of organic pollutants in neutral and alkaline wastewater and reduce the formation of iron sludge. The improved PC process does not require any additional oxidants or catalysts, nor does it need to adjust the pH of the wastewater in advance but can directly treat actual wastewater, achieving a target pollutant (C12H14N4O2S, sulfamethazine) removal of 87%-100% within 60 min and TOC removal of 46–76% within 240 min with the corresponding energy consumption below 0.02 kWh gTOC-1. Compared with the conventional PC process, this improved process could produce hydroxyl radical (•OH) and superoxide radical (O2•-) more efficiently, which greatly increased the SMT removal rate constant by 3–4 times and oxidative removal proportion of organic pollutants from 42 ∼ 47% to 85 ∼ 90%. Thanks to the Fe(II) regeneration capacity of MCF to promote iron circulation, the yield of •OH was 4.1 times higher while the iron sludge production was less than a quarter when compared with that of conventional PC. The improved PC process illustrated better purification performance and lower energy consumption for actual wastewaters such as pharmaceutical wastewater, surface water and rural decentralized domestic sewage than the conventional PC process. Our work elucidated the mechanism of promoting Fe(II) regeneration through MCF cathode under alkaline conditions to enhance •OH production and O2•- oxidation, showing a good environmental application prospect.