Effect And Mechanisms Of Dechlorane Plus On The Production Of Short-chain Fatty Acids From Anaerpbic Fermentation Of Waste Activated Sludge

Anaerobic fermentation technology,as a mature energy technology of solid waste,is widely used these years,because of its low cost and low combustion pollution.In the process of anaerobic fermentation,the organic matter in the sludge can be biologically converted into organic energy substances such as H₂,short-chain fatty acids（SCFAs）,CH₄,etc..Among them,short-chain fatty acids can not only be used as a high-quality carbon source to enhance biological nutrient removal（EBNR）performance,but also can be used as raw materials to synthesize degradable bioplastics,as well as short-chain fatty acids can be directly entered into the microbial electrochemical system（MES）for biological electricity generation.Based on the wide application prospects of short-chain fatty acids,acid production during anaerobic fermentation of sludge has attracted more and more attention.With the rapid development of social economy and urbanization,emerging organic contaminants（ECs）are produced in large quantities,which are toxic and harmful and difficult to degrade.Dechlorane Plus,an organochlorine aliphatic flame retardant,has excellent characteristics such as low toxicity and high ignition point,which currently become one of the most widely used and studied flame retardant substances.However,DPs will be transferred to the sludge through adsorption,etc.due to high degree of hydrophobicity and lipophilicity.In addition,DPs have good stability which are difficult to be degraded by organisms and natural light,they can exist stably in the environment for a long time,thus DPs pose a potential threat to the further resource utilization of sludge.This project is based on the"Three Principles"of solid waste（harmless,reduction,and resource utilization）and"3R Principles"（Reduce,Reuse,Recycle）,and the main purpose of this study is to explore the potential impact of an emerging contaminants Dechlorane Plus on the anaerobic fermentation of waste activated sludge.First of all,the optimal p H value condition of the DPs for anaerobic fermentation of sludge to produce SCFA was initially determined,which provided a basis for subsequent research.The study found that adjusting the p H value can effectively effect the amount of SCFA produced,and the amount of SCFA production in the alkaline environment is significantly higher than that in the neutral and acidic environment.In addition,soluble chemical oxygen demand（SCOD）,soluble protein and soluble polysaccharide in the alkaline environment in the waste activated sludge are higher than that in the acidic environment and the neutral environment,so when the p H value is 10,it is the best environment to produce SCFA.After that,the effect of different doses of Dechlorane Plus on the production of short-chain fatty acids during the anaerobic fermentation of sludge was studied,shown that the presence of DPs will affect the acid production of waste activated sludge by anaerobic fermentation,and the higher the content of DPs,the stronger the inhibitory effect and the less the amount of SCFA produced,as well as the SCFA component analysis shows that the presence of DPs inhibits acid production mainly by reducing the amount of acetic acid.Then,the mechanism of Dechlorane Plus on the anaerobic fermentation of sludge was studied,including its effects on the various processes during anaerobic fermentation,the research results show that under the influence of DPs,the physical characteristics of sludge particles will be promoted,but the presence of DPs has an inhibitory effect on the content of soluble organic matters in waste activated sludge,and the higher the content of DPs,the lower the content of soluble organic matters.The presence of DPs will also reduce the content of EPS in waste activated sludge,and the higher the content of DPs,the more obvious the reduction of EPS content,and it mainly affects the content of EPS in the fermentation system by reducing the content of S-EPS.It through 3D-EEM,FT-IR measurements shows that the addition of DPs inhibited the production of humic acid and fulvic acid,which inhibited the anaerobic acidification process to a certain extent.In addition,high doses of DPs would lead to more release of NH₄⁺-N and PO₄^3--P in waste activated sludge.Finally,when the Dechlorane Plus appeared,the enzyme activity related to acid production in the fermentation system and the change of the microbial community were analyzed.Through high-throughput Illumina Miseq sequencing and community analysis,it is shown that high content of DPs will affect the abundance of bacterial communities.DPs reduces the levels of Firmicutes and Actinobacteria at the phylum level,which is also one of the important reasons for the reduction of SCFA.In addition,at the genus level,the presence of the DPs reduces the relative abundance of the typical acid-producing microorganism Proteiniclasticum produced by SCFA.What is more,in the analysis of the population structure of archaea,at the genus level the presence of DPs can inhibit the activity of the acetic acid-trophic archaea Methanocorpusculum,Methanosaeta,and the only methanogenic microbe Methanosarcina which can utilize 3different methane biosynthesis pathways,and slow down the speed to consume SCFA during anaerobic fermentation process,but the presence of DPs has little effect on hydrogen-trophic methanogens such as Methanobrevibacter and Methanospirillum,and Methanomethylovorans which belong to methyl methanogens.During the later fermentation stage,the influence of DPs on the activities of protease,α-glucosidase and acetate kinase shows an inhibitory effect as the concentration of DPs increases,but the activity of butyrate kinase is promoted with the increase of DPs content,as well as different dosage of DPs concentration has little effect on the co-enzyme F420 in the methanation stage and the enzyme CODH which related to microbial activity.The research results of this paper effectively fill the gap in the research on the interaction between sludge anaerobic fermentation and emerging contaminants,which in line with the principles of harmlessness,reduction and resource utilization of solid waste treatment in my country,and have important reference significance for the future sludge treatment and resource utilization.