Influence Of Sulfamethoxazole On Anaerobic Digestion And The Characterization Of Biochar Regulation

Since the introduction of penicillin,various types of antibiotics have been used in clinical medicine,livestock farming and the aquaculture industry,and subsequently enter the natural environment in the form of human and animal waste.Anaerobic digestion,the most typical wastewater treatment technology,is widely used as it can reduce the concentration of antibiotics while treating wastewater.However,the residual antibiotics in faeces and urine not only inhibit the toxicity of microorganisms,but may also cause environmental risk problems during treatment and disposal.To address this problem,this study investigated the toxic inhibition of anaerobic fermentation by the typical antibiotic sulfamethoxazole(SMX),and investigated the mediating effect of biochar on the anaerobic fermentation system under the inhibition of SMX and its regulatory principles.The main contents and results are as follows:(1)To investigate the effects of different concentrations of SMX on the anaerobic fermentation system,and to analyse the feasibility of 500°C pyrolysis of wood-chip biochar for enhancing the methanogenic efficiency of the anaerobic fermentation system under SMX toxicity stress and the multivariate response of microorganisms in the anaerobic digestion system.It was found that,for one,the toxic inhibition effect of SMX at different concentrations(0.5-50 mg/L)on the anaerobic fermentation system increased with its concentration,and the cumulative methane production of the system decreased by 9.63% and the maximum specific methane production rate decreased by38.66% when the SMX concentration reached 50 mg/L.The addition of wood chip biochar was able to increase the cumulative methane production of the system by15.40% and the methanogenic potential by 15.40%.Secondly,the system showed serious accumulation of propionic acid at high SMX concentrations up to 1073 mg/L.The addition of wood-chip biochar reduced the propionic acid content of the anaerobic digestion system by 90.79%,effectively alleviating the excessive accumulation of volatile fatty acids(VFA)caused by SMX.Thirdly,the secretion of protein and polysaccharide components of the sludge extracellular polymer(EPS)increased with increasing SMX concentration.Wood chip biochar was also able to increase the activity of the microbial electron transfer system in the system by 0.28-0.43 INTF/(g TSS-h)under SMX inhibition,which inferred that wood chip biochar could enhance the efficiency of mutualistic oxidation and methane production by promoting microbial intermediate electron transfer.Fourthly,the addition of wood chip biochar not only increased the degradation efficiency of SMX by 6.7 times in the early stage of the reaction,but also significantly reduced the degradation time of SMX in the system.(2)To investigate the mitigation of the toxic effect of biochar on the anaerobic fermentation system under the continuous stress of high SMX concentration,the regulation of SMX migration and transformation,and the multidimensional response of microorganisms in the anaerobic fermentation system before and after biochar-mediated SMX toxicity.First,the inhibition of SMX toxicity increased with increasing SMX concentration,but the system could improve its tolerance to SMX toxicity through microbial domestication.300 mg/L SMX inhibition decreased the cumulative methane production by 13.00% and the maximum specific methane production rate by10.56%,while 700 °C biochar and GAC injection increased the cumulative methane production by The addition of 700°C biochar and GAC increased the cumulative methane production by 2.90-11.48% and increased the maximum specific methane production rate by 1.85-5.57%,but could not completely alleviate the inhibition of the system by the high SMX concentration.In addition,the accumulation of VFAs dominated by acetic acid and propionic acid occurred in the system under the toxic inhibition of 300mg/L SMX.Both 700°C biochar and GAC accelerated the conversion of acetic acid and propionic acid,effectively alleviating the accumulation of acid in the system.Secondly,the secretion of protein-like fractions in microbial EPS was increased by22.02-95.39%under 300 mg/L SMX stimulation,and biochar was able to reduce it by 1.44-57.29%.(3)The effect of biochar injection on the degradation efficiency and migration transformation pathway of SMX in anaerobic fermentation system under 300 mg/L SMX toxicity inhibition was investigated.The results showed that although the microorganisms were able to degrade SMX through their own growth and metabolism after two cycles of domestication,the addition of biochar increased the degradation efficiency of SMX by 13.0-40.4% overall and doubled the reaction time.On the other hand,the intermediates and metabolic pathways of SMX degradation were changed to a certain extent before and after biochar mediation.Combined with the prediction results of ECOSAR model,it was found that biochar was able to regulate the degradation pathways of SMX by inducing the production of some low molecular weight and low biotoxic compounds.(4)The changes in microbial populations in the anaerobic fermentation system before and after biochar-mediated SMX toxicity were analyzed.The results showed that the addition of biochar induced a shift from Firmicutes to Chloroflexi,which may facilitate VFA mutualistic metabolism;elevated the abundance of propionate oxidizing bacteria Candidatus＿Cloacamonas,which alleviated propionate accumulation in the system;elevated the relative abundance of Anaerolineaceae and Methanothrix in relative abundance,mediating direct interspecific electron transfer between bacteria and archaea.