Dual strategies to enhance mineralization efficiency in innovative electrochemical advanced oxidation processes using natural air diffusion electrode: Improving both H2O2 production and utilization efficiency

High mineralization efficiency and low energy consumption are the core requirements for the application of electrochemical advanced oxidation processes (EAOPs) for organic pollutants degradation. Herein we reported innovative EAOPs using natural air diffusion electrode (NADE) to improve H2O2 production and enhanced utilization efficiency by combination with electro-Fenton and photoelectro-Fenton (EF-PEF) for the degradation of 2,4-dichlorophenoxyacetic acid. At 0.2 and 1.2 A, the H2O2 production on NADE possessed 158% and 188% of that on normal aeration electrode (AE) with the total energy consumption only 7.2% and 25.4% of that on AE, respectively. Such excellent H2O2 production performance on NADE was attributed to ultra-high oxygen mass transfer efficiency and the feature of not requiring aeration, which reduced energy consumption greatly. A new H2O2 utilization efficiency (HUE) evaluation index including decomposition ratio, conversion efficiency and total utilization efficiency of H2O2 was proposed, demonstrating that PEF had a higher HUE than EF but not costeffective due to a higher energy consumption. EF-PEF was thus proposed to upgrade the traditional PEF, which reduced energy consumption while maintained high mineralization efficiency. The HUE in EF-PEF process was greatly improved and superior to most reported EAOPs in literatures, which explained the high mineralization efficiency (78%?87%) with an extremely low energy consumption (0.065?0.167 kWh (g TOC)-1) even an order of magnitude lower than that in the literatures. This work enlightened the importance of two strategies of improving both H2O2 production and utilization efficiency to maintain high mineralization efficiency in H2O2 based EAOPs.