The Mechanism Of The Effect Of Sulfoxaflor On The Process Of Anaerobic Digestion

As a new sulfoximine insecticide,sulfoxaflor has been used in the world since its introduction.However,studies have shown that the residues of sulfoxaflor can still be detected in brown rice,rice straw and paddy water after field application,and it has certain toxicity to many non-target organisms such as earthworms and bumblebees,which attracts people’s attention.A large amount of waste water will be produced by sulfoxaflor in the production process or after it is applied in the field,which will eventually enter the sewage treatment plant.and sulfoxaflor will inevitably accumulate in anaerobic sludge.Anaerobic digestion,as a biotechnology that can stabilize,harmless,reduce and recycle organic matter,is driven by a series of biochemical processes and functional microorganisms,and the existence of sulfoxaflor may have a certain impact on the microbial activities in it.However,up to now,the influence of sulfoxaflor on anaerobic digestion of sludge has not been systematically analyzed.Therefore,this study focused on the above problems and the shortcomings of current research,and made a preliminary exploration from the aspects of the interaction between sulfoxaflor and anaerobic granular sludge,the influence of sulfoxaflor on anaerobic digestion process,and the influence on methanogens.The main research results are as follows:(1)The interaction between anaerobic granular sludge and sulfoxaflor was studied.Adsorption experiments were carried out on anaerobic granular sludge before and after removal of extracellular polymer substances(EPS).It was found that the adsorption effect of original anaerobic granular sludge was obviously better than that of granular sludge after removal of EPS,which indicated that EPS played a very important role in the adsorption process of anaerobic granular sludge.Compared with the blank control group,the concentration of protein and polysaccharide in the experimental group added with sulfoxaflor increased.In addition,FTIR,3D-EEM,XPS and other methods were used to analyze the changes of extracellular polymers.The results showed that sulfoxaflor changed or destroyed the secondary structure of EPS protein,thus improving the biological flocculation ability of sludge.In addition,sulfoxaflor mainly reacts with amide groups,carbonyl groups,side chains of amino acids or lipids in EPS.In addition,the adsorption kinetics of sulfoxaflor by anaerobic granular sludge accords with quasi-second-order kinetic equation,and the thermodynamic process accords with Freundlich isothermal adsorption model.Adsorption of sulfoxaflor on sludge is an endothermic process.With the increase of temperature,the adsorption capacity increases,while the adsorption capacity decreases with the increase of pH value.Metal ions Ca2+ and Cu2+can promote the adsorption of sulfoxaflor on sludge to a certain extent.(2)The effect of sulfoxaflor on anaerobic digestion system was studied.With the increase of the concentration of sulfoxaflor,the methane yield and total volatile fatty acids(VFAs)content in the system gradually decreased.By analyzing the microbial community in anaerobic digestion system,it was found that the addition of sulfoxaflor would change the microbial community structure in anaerobic granular sludge.At the gate level,with the increase of the concentration of sulfoxaflor,the dominant population of the community changed,and Chloroflexi gradually replaced Bacteroidota as the richest gate,and its relative abundance increased from 22.3%to 29.4%.At the genus level,with the increase of the concentration of sulfoxaflor,the relative abundance of acid-producing fermentation bacteria(Macellibacteria,Trichococcus and Enterococcus)decreased significantly,reaching a maximum of 12.6%.The relative abundance of bacteria(such as norank-Anaerolineae and involved in the degradation of complex organic matter has increased to a maximum of 7.2%.On the other hand,for the archaea community in anaerobic digestion system,the relative abundance of methanogens will not change significantly with the addition of sulfoxaflor.(3)Based on the acute toxicity of sulfoxaflor to M.acetivorans C2A,the effect of sulfoxaflor on methanogenic bacteria was explored,and the mechanism of its influence on methane production in anaerobic digestion was revealed.The results showed that although sulfoxaflor did not significantly inhibit the growth of M.acetivorans C2A,with the increase of sulfoxaflor concentration,the methane yield decreased and the CH4/OD600 value decreased from 50.05 to 10.24 mL;Compared with the blank group,214 differentially expressed genes,including 198 up-regulated genes and 16 down-regulated genes,were obtained from the transcriptome of the strain M.acetivorans C2A exposed by sulfoxaflor.Sulfoxaflor can enter the cell and affect its methane production function by increasing the permeability of cell membrane and enhancing the transport function of multi-drug ABC transporter and MFS transporter.The quantitative analysis of functional genes and qRT-PCR showed that sulfoxaflor may affect the conversion of methanol to methane by inhibiting the expression of mcrA and MtaA genes in the metabolic pathway of methane production in M.acetivorans C2A,thus reducing its methane production.