Efficacy of a two-compartment electrochemical flow cell introduced into a reagent-free UV/chlorine advanced oxidation process

[Display omitted] •A reagent-free UV/chlorine process was established using an flow cell.•The flow cell can concentrate Cl− from wastewater to the UV reactor.•The flow cell can acidify the solution in the UV photochemical reactor.•The Cl− condensation and the acidification enhanced the process performance.•The EEO observed was superior to that of other UV/electro-chlorine systems. As the advanced oxidation process of ultraviolet photolysis of chlorine (UV/chlorine) is more effective under an acidic condition than under a basic one, it requires reagent addition to keep the solution pH acidic and to supply free chlorine. In this study, a two-compartment electrochemical flow cell with an anion exchange membrane as a diaphragm was introduced into a UV/chlorine reactor for realizing a reagent-free operation using anodically produced protons and free chlorine. As a result, wastewater in the anodic compartment was successfully acidified by the protons generated through the water discharge at the anode, by the hydrolysis of electrochemically generated chlorine, and by the inhibition of the hydroxide ion supply from the cathodic compartment by the diaphragm. Furthermore, the electrochemical chlorine production was enhanced by increasing the chloride ion concentration in the anodic compartment through the electrodialysis effect. As the acidic effluent from the reactor was finally neutralized by hydroxide ions generated by the water discharge at the cathode, it was demonstrated that the proposed UV/electro-chlorine advanced oxidation process could work well without reagent addition. The electrical energy per order (EEO) of the process was estimated to be 15.7 kWh/(m3 order), which was comparable to that of the conventional advanced oxidation processes.