Comparative study of electrochemical water treatment processes for a tannery wastewater effluent

• Comparison of tannery wastewater treatment by EC, EOx, EF and PEF processes.
• Efficiency increased in the order EOx < EC ∼ EF < PEF after 180 min.
• EC/PEF gave higher organic removal being able to yield 90% TOC reduction.

Comparison of tannery wastewater treatment results of electrocoagulation (EC), electro-oxidation (EOx), electro-Fenton (EF) and photoelectro-Fenton (PEF) processes using two current densities was performed and employed no only to assess the best electrochemical approach but also to have elements to suggest a combined and cost effective process. In this way, iron plates were used as the anode and cathode in the EC tests. For the EOx process, a boron-doped diamond (BDD) thin-film electrode was used as the anode, and an iron plate was employed as the cathode. For the EF and PEF treatments, both electrodes were of BDD and H2O2 was produced by O2 reduction at the cathode surface. Electrolytic trials were carried out in stirred open tank reactors containing 250 mL of wastewater applying either 65 or 111 mA cm−2. In PEF trials, the wastewater was irradiated using a 6 W UVA light source. The characterization of the sludge generated in the EC process showed that it was not dangerous for the environment. Total Organic Carbon (TOC) removal values were larger at the highest density. Higher mineralization on the other hand, was found in EF and PEF when the concentration of Fe2+ was 3.0 instead 1.0 mM. Comparison of the methods revealed that their efficiency to remove the organic pollutant increased in the order EOx < EC ∼ EF < PEF after 180 min of electrolysis. Furthermore, the information obtained from the study, also allowed designing a combined strategy aimed to produce an effluent suitable for discharge. The combination of EC followed by PEF was also studied. The results showed that the EC/PEF treatment gave higher organic removal than EC and was more economic than PEF, being able to yield 90% TOC reduction of the tannery wastewater.