Effects of oxidation–reduction potential control and sequential use of biological treatment on the electrochemical Fenton-type process

[Display omitted] •The ORP control was introduced into the electrochemical Fenton-type (EFT) process.•The ORP control could improve the current efficiency from 16.9% to around 80%.•The EFT process was applied to an actual wastewater contaminated with 1,4-dioxane.•The EFT process with a biological process effectively removed COD and 1,4-dioxane. This paper reports on the effects of an oxidation–reduction potential (ORP) control on the electrochemical Fenton-type process (EFT process) and the efficacy of a combined approach, namely, the EFT process with an ORP control together with an activated sludge process, on the treatment of wastewater contaminated with 1,4-dioxane. The EFT process with an ORP control was able to improve the current efficiency from 16.9% to 73.6–81.9%. A superior performance for both the current efficiency and the treated water quality was recorded by the EFT process with an ORP control of 1000mV. This superior result was ascribed to the approach preventing an excessive accumulation of hypochlorous acid. Two combined processes, namely, an activated sludge process followed by the EFT process with an ORP control (AS-EFT process) and the EFT process with an ORP control followed by an activated sludge process (EFT-AS process), were examined by using 1,4-dioxane contaminated municipal wastewater. As a result, the AS-EFT process was superior to the EFT-AS process in respects of both energy consumption and the performance of chemical oxygen demand (COD) removal, as well as the removal of 1,4-dioxane, due to the smaller COD loading onto the EFT reactor in the AS-EFT process.