Novel electrodes for cathode electro-Fenton oxidation coupled with anodic oxidation system for advanced treatment of livestock wastewater

Abstract

With the rapid development of livestock industry, a large amount of livestock wastewater generates in China in recent years. The conventional treatment process for livestock wastewater, including anaerobic digestion and anoxic-oxic treatment, is very common in China for the low operational cost. However, the very low BOD5/CODCr ratio (<0.1) in the associated effluent renders the further treatment process very difficult. In this study, a PbO2 anode coupled with a 2-ethylanthraquinone (EAQ)-modified graphite felt cathode was used to treat the livestock wastewater (BOD5/CODCr < 0.1) discharged from the conventional two-stage anoxic/oxic (A/O) process. The results of scan electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fourier transforminfrared spectroscopy (FTIR) show that the prepared PbO2 electrode has a smaller crystal size, higher oxygen evolution reaction (OER) potential and an excellent electro-catalytic performance compared to a purchased PbO2 electrode, and the EAQ-modified graphite felt cathode has a higher content of oxygen-containing functional groups and higher oxygen reduction reaction (ORR) electro-catalytic performance than pristine graphite felt. The results of the electrolysis experiment showed that the BOD5/CODCr ratio was increased from 0.084 to 0.42 with 71.5% CODCr removal after 80 min of electrolysis, when the Fe2+ concentration was 0.3 mM. The .OH produced in the electrolysis system was captured successfully by electron paramagnetic resonance (EPR).