The Study On The Degradation Mechanism Of Trichlorophenol By Intimate Coupling Of Photocatalysis And Microbial Fuel Cells

2,4,6-trichlorophenol（TCP）is a common"mutagenesis,carcinogenesis,teratoeenesis"refractory organic pollutant,which is often found in papermaking wastewater and printing wastewater.However,traditional biological methods are not suitable for TCP wastewater treatment due to its high biological toxicity.Microbial fuel cells（MFC）are renewable technologies utilizing microorganisms as catalyst to degrade organic pollutants for wastewater treatment with simultaneous electricity generation.However,electrogenic microorganisms in microbial fuel cells are more inclined to utilize easily biodegradable organics as electron donors,and their ability to process bio-refractory organic pollutants is limited.Here in this study,we proposed a strategy of intimate coupling of photocatalysis and microbial fuel cells,by using photocatalysis to initiate the transformation of the refractory organics to readily biodegradable products that could be sequentially utilized by electrogenic microorganisms.The study includes the following sections:（1）In this study,mpg-C₃N₄ photocatalytic materials with different template ratios were prepared by the hard template method.The degradation efficiency of TCP reached 65.4%,which is the highest when the mass ratio of the template agent silica to the precursor ammonium thiocyanate was 0.4.The stability of mpg-C₃N₄ photocatalyst was confirmed with cycling stability test and XRD analysis.Two degradation pathways were revealed and determined with the intermediate products and DFT calculations:（a）2,4-Dichlorophenol,4-chlorophenol,phenol and benzoquinone,which were obtained by the attack of·OH via a series of dechlorination reactions,were eventually oxidized to CO₂ and H₂O;（b）-Cl on the benzene ring of TCP was replaced with-OH to generate the 2,6-dichlorohydroquinone,and then dechlorinated to produce phenylhydrazine,which was eventually degraded to CO₂ and H₂O.（2）The mpg-C₃N₄ photocatalyst was coupled to the carbon felt electrode to prepare the MFC photo-anode,which was used in photocatalysis-MFC to degrade TCP of different concentrations.MFCs with the illuminated photo-anode（closed circuit）,bio-anode（closed circuit）,photo-anode（non-illuminated,open circuit）and bio-anode（open circuit）achieved TCP degradation efficiencies of 80.2%,66.5%,56.7%and 47.3%respectively with an original concentration of 200 mg L^-1,with the photo-anode（illuminated,closed circuit）in MFC achieved the best performance.In addition,the output voltage of the illuminated photo-anode increased by 54 mV and the power density by the photo-anode(19.8 W m^-3)was¹3%higher than that of a bio-anode(17.6 W m^-3).The degradation pathway of TCP in the photocatalysis-MFC coupled system could be identified as the photocatalytic pathway and the MFC pathway.Dechlorination reaction was mianly involved in the photocatalytic pathway,while it was revealed in the MFC pathway that-Cl on the benzene ring of TCP was replaced with-OH and then oxidized by·OH to destroy the phenyl structure to produce ketoadipic acid,which was eventually oxidized to CO₂ and H₂O.（3）The community structure on the anode and cathode in different MFC systems were analyzed by the high-throughput sequencing method.When sodium acetate was used as the substrate,the anodic microorganisms in the MFC were mainly electricigens Geobacter,whereas when using TCP as the substrate,the anodic microorganisms in the MFC were mainly electricigens Pseudomonas which had a strong tolerance on pollutants;Extracellular electrobacterium in the anodic microorganisms showed the highest abundance,while Rhodococcus dominated in the cathode microorganisms,which might be responsible for the degradation of aromatic organic compounds.