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

Highlights: • The mechanism of GF modification by EQA was studied. • The surface crystal of the prepared PbO₂ is denser. • The advanced treatment mechanism of livestock wastewater treatment was studied. • The produced ^.OH was captured successfully by electron paramagnetic resonance (EPR). • The novel electrolysis system increases the biodegradability of wastewater by 400%. -- 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/COD_Cr 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 (BOD_5/COD_Cr < 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/COD_Cr ratio was increased from 0.084 to 0.42 with 71.5% COD_Cr 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).