Enhancing electrochemical treatment of nitrogen-containing organic wastewater by iron filings: Performance, inhibition of organochlorine by-products accumulation and cost-effectiveness

Low current efficiency and the formation of organochlorine by-products were the critical bottlenecks in the practical applicability of electrochemical oxidation technology for nitrogen-containing organic wastewater (NCOW) treatment. In this study, a filled-bed electrochemical system with waste iron filings (IFES) was constructed to enhance the removal efficiency of total nitrogen (TN) and chemical oxygen demand (COD) as well as inhibition of the accumulation of the organochlorine by-products. Biologically treated landfill leachate (BTLL) was selected as a typical NCOW source to evaluate the performance of IFES. Cyclic voltammetry, X-ray photoelectron spectroscopy, and potentiometric analysis showed that due to the polarization effect of iron filings and the environment with low redox potential was created by the evolution of iron compounds, IFES could significantly improve the current efficiency of TN removal. Electron paramagnetic resonance analysis revealed that the reaction of low binding energy iron compounds dissolved from the polarization process of iron filings with available chlorine could promote the formation of hydroxyl radicals and can enhance the removal efficiency of COD. It was also proved that the accumulation of organochlorine could also be reduced by the reduction process of Fe-0/Fe2+, and by the iron filings polarized cathode. Besides, compared with the traditional electrochemical oxidation process, IFES can significantly decrease the energy consumption of BTLL treatment under the same treatment effect, which was conducive to reducing the engineering costs caused by the power loss. The IFES was proved to be a feasible alternative for the modification of existing electrochemical oxidation practical engineering.