Preparation of CeO-doped carbon nanotubes cathode and its mechanism for advanced treatment of pig farm wastewater.

The effluent from conventional treatment process (including anaerobic digestion and anoxic-oxic treatment) for pig farm wastewater was difficult to treat due to its low ratio of biochemical oxygen demand to chemical oxygen demand (BOD/COD) (<0.1). In the present study, electro-Fenton (EF) was used to improve the biodegradability of the mentioned effluent and the properties of self-prepared CeO-doped multi-wall carbon nanotubes (MWCNTs) electrodes were also studied. An excellent HO production (165 mg L) was recorded, after an 80-min electrolysis, when the mass ratio of MWCNTs, CeO and pore-forming agent (NHHCO) was 6:1:1. Results of scanning electron microscopy (SEM), transmission electron microscope (TEM) and x-ray photoelectron spectroscopy (XPS) showed that addition of NHHCO and the doping of CeO could increase the superficial area of the electrode as well as the oxygen reduction reaction (ORR) electro-catalytic performance. The BOD/COD of the wastewater from the first stage AO process increased from 0.08 to 0.45 and COD reduced 71.5% after an 80-min electrolysis, with 0.3 mM Fe solution. The non-biodegradable chemical pollutants from the first stage AO process were degraded by EF. The non-biodegradable pollutants identified by LC-MS/MS in the effluent from AO process including aminopyrine, oxadixyl and 3-methyl-2-quinoxalinecarboxylic acid could be degraded by EF process, with the removal rates of 81.86%, 34.39% and 7.13% in 80 min, and oxytetracycline with the removal rate of 100% in 20 min. Therefore, electro-Fenton with the new CeO-doped MWCNTs cathode electrode will be a promising supplement for advanced treatment of pig farm wastewater.