Effect Of Dibutyl Phthalate On Anaerobic Digestion Of Chicken Manure

Phthalate esters（PAEs）,commonly used as plasticizers in the market,have been detected in livestock feed and poultry feces in recent years.Anaerobic digestion is an important method for the resource utilization of chicken manure,but the effect of PAEs,specifically di-n-butyl phthalate（DBP）,on the anaerobic digestion of chicken manure remains unclear.In this study,chicken manure was used as the fermentation material,and DBP,a typical PAEs compound,was selected as the research object.Batch and continuous experiments were conducted to investigate the impact of DBP on the anaerobic digestion of chicken manure.The study aimed to elucidate the influence of different DBP concentrations on methane production during anaerobic digestion,clarify the removal pattern of DBP during anaerobic digestion,and reveal the microbiological mechanisms underlying the impact of DBP on methane production in chicken manure anaerobic digestion.The results of this study are summarized as follows:（1）Under batch experiment conditions,low concentrations of DBP(0-300 mg·L^-1)had no significant impact on the gas production characteristics of the anaerobic digestion of chicken manure.When the DBP concentration was 300 and 500 mg·L^-1,the methane inhibition rate of anaerobic digestion of chicken manure was 7.3%.Methanogenesis became the limiting step in anaerobic digestion,and the accumulation of large molecular organic acids was observed.Under continuous experiment conditions,as the DBP concentration increased,the methane production rate during anaerobic digestion gradually decreased,with the highest methane inhibition rate reaching 82.75%.（2）Under continuous experiment conditions,the total extracellular polymeric substances（EPS）concentration of anaerobic sludge increased by 16.86%to 96.63%when DBP was added at different operational stages.The proportion of bound EPS（T-EPS）increased,while soluble EPS（S-EPS）proportion decreased,and the content of EPS polysaccharides increased.Throughout the operational stages of S4 to S7,the ammonia nitrogen concentration in the anaerobic digestion system remained between 800±45.17 mg·L^-1 and 2712±35.81 mg·L^-1.There was no significant increase in the ammonia nitrogen concentration at different operational stages with DBP addition.This could be attributed to the enhanced activity of resistant microorganisms in the sludge under continuous experiment conditions,allowing the ammonia nitrogen generated from organic matter hydrolysis to be utilized by the resistant microbial synthesis process.（3）The dominant microbial groups in the anaerobic digestion of chicken manure were related to protein degradation,including the phyla Firmicutes,Proteobacteria,and Bacteroidota.As the DBP concentration increased,the relative abundance of Firmicutes and Bacteroidetes decreased,while Proteobacteria increased.Pseudomonas and Acinetobacter were identified as potential key DBP-degrading bacteria among the Proteobacteria.With the increasing DBP concentration,the dominant methane-producing archaea shifted from the acetoclastic Methanosaeta to the hydrogenotrophic Methanobacterium.（4）As the DBP concentration increased,the degradation rate of DBP ranged from 39.48%to 87.93%.Residual DBP in the anaerobic digestion system mainly existed in the solid phase through adsorption.The increased DBP degradation rate might be attributed to the domestication effect on anaerobic microorganisms as the DBP concentration gradually increased,leading to the dominance of DBP-degrading bacteria in the anaerobic digestion system.