Pretreatment-anaerobic Digestion Process Enhances Fecal Sludge Treatment And Mechanism Of Microbiome Response

Fecal sludge indicates the human feces that haven’t entered the drainage system and are stored in the initial position of sanitary system,including septic tanks and household toilets.Untreated fecal sludge will not only pollute the natural water,but also has the risk of transmission of pathogenic microorganisms.Therefore,to stabilize and sanitate the fecal sludge is of great significance.The traditional septic tank fecal sludge treatment process can not only initially complete the separation process between solid and liquid,but also decompose organic matter and kill various pathogenic microorganisms through anaerobic digestion.However,there is a large amount of non-soluble organic matter during the process of organic matter decomposition of fecal sludge,which often leads to a slow hydrolysis rate of organic matter in system and a low efficiency of fecal sludge reduction.Therefore,septic tanks shall be cleaned regularly to reserve the room for normal operation at this moment.The sludge reduction and disposal problem is an urgent research subject in post-pandemic era.In addition,fecal sludge is also an important infectious medium for some diseases of human.The acceleration on hydrolysis rate of sludge and inactivating pathogenic microorganisms in sludge have become the core issues of fecal sludge disposal.The subject investigates the effects of chemical pretreatment on hydrolysis of fecal sludge,solid reduction and subsequent anaerobic digestion efficiency,and removes the tetracycline through connecting the pretreated and anaerobic digested fecal sludge into the soil microbial electrochemical system.In addition,based on the microbiome technology,the subject revealed the succession law of microbial（bacteria and viruses）community structure of fecal sludge in different pretreatment methods and anaerobic digestion processes,and the response mechanism of functional microorganisms in Soil Microbial Fuel Cell（SMFC）to fermentation products.Meanwhile,combining the macro transcriptomic sequencing technology,the subject clarifies metabolic regulatory mechanism of functional microorganisms during pretreatment and anaerobic digestion.The subject constructs a“Pretreatment-Anaerobic Digestion-Microbial Electrochemistry”composite process,which realizes the whole process of reducing and harmlessness of human fecal sludge.First,the subject studies the effect of Potassium Ferrate（PF）and Peroxymonosulfate（PMS）pretreatment on the release of soluble organic matter and solid reduction of fecal sludge.The results show that PF pretreatment realizes the best performance on the release of soluble organic matter and solid reduction in fecal sludge.After being pretreated with PF for 120 min,Soluble Chemical Oxygen Demand（SCOD）increases by 3117.0 mg/L,and Volatile Solid（VS）decreases by 79.2%.Then,through comparing the effects of different pretreatment methods on anaerobic digestion efficiency of subsequent fecal sludge,we find that PF pretreatment is capable of better promoting the acid production and gas production of fecal sludge,and there are 38.2ml methane and 7355mg/L volatile fatty acids are produced respectively within 9 days.Finally,the common removal of fecal sludge and tetracycline can be enhanced by the microbial electrochemistry system during the process of advanced treatment and recycling of fecal sludge after anaerobic digestion.The results show that the electrochemistry efficiency of reactor is greatly improved by adding the fecal sludge with pretreatment of PF and anaerobic digestion.SCOD degradation rate of fecal sludge in SMFC reaches 95.27%within 25 days.The removal rate of Tetracycline（TC）in the leaching solution at the electrode（64.5%）is higher than that of the unmixed pre-oxidized fecal sludge reactor（25.2%）.The results of 16S r RNA gene high-throughput sequencing show that different pretreatment methods and anaerobic digestion processes reshaped the community structure of fecal sludge.All pretreatment methods,excluding alkaline（ALK）,show an inactivation effect on E.coli and worm eggs.For PF pretreatment group,the dominant genera of microorganisms in fecal sludge before and after anaerobic digestion are Bacteroides and Macellibacteroides respectively;for ALK and NaClO pretreatment groups,the dominant genus is Romboutsia.After anaerobic digestion,the dominant genera of ALK-AD and NaClO-AD fecal sludge are transformed into Escherichia and Salipaludibacillus.Through the evaluation on virus inactivation during the process of fecal sludge pretreatment and anaerobic digestion by viromics,the subject finds that the main virus in all samples is phage.ALK,PF and NaClO pretreatment and anaerobic digestion change the composition of phage in fecal sludge.E.coli phages belong to Inoviridae family,whose relative abundances in ALK and PF pretreatment reach 88.42%and 67.26%respectively,and decrease by 86.27%and 67.11%respectively after anaerobic digestion.Meanwhile,the subject evaluates the influence of pretreated fecal sludge fermentation broth and biogas residue on the microbial community structure of the anode of the microbial electrochemical system,and finds that the main electroactive bacteria of anode of reactor pretreated with PF and anaerobic digested fecal sludge are Desulfuromonas,and the dominant species of cathode biofilm is Pseudomonas.Meanwhile,the subject explores the response of microbial functional genes in fecal sludge to pretreatment and anaerobic digestion.The highly expressed genes of carbohydrate metabolism,energy metabolism and ribosome metabolism of microorganisms in pretreated and anaerobic digested fecal sludge indicates that anaerobic digestion enhances the growth and metabolism of microorganisms.In ALK-AD and PF-AD samples,the Differentially Expressed Genes（DEGs）of glycolysis,pyruvate metabolism,and lactate metabolism are expressed upward,of which the representative genes include the gene encoding ferredoxin（korA and vorB）.korA,vorB and gapA,the genes related to glycolysis pathway,are expressed upward in PF-AD vs UP-AD.These three genes are all involved in regulating the production of short chain volatile fatty acids,and are mainly exist in the species of Clostridium.Therefore,the anaerobic digested fecal sludge produces the most VFAs after PF pretreatment(total VFAs in 7355 mg/L are produced on 9^th day of anaerobic digestion).In addition,double component system,ABC transmembrane transport system and ribosome synthesis related genes（glnA,cydA,cydB and ompC）are also expressed upward in ALK-AD and PF-AD,which indicates that microbial cell signaling system produced stress responses to pretreatment and anaerobic digestion.Partial microorganisms adapt to selective pressure and become the dominant species in pretreatment stage and anaerobic digestion stage.In conclusion,the research constructs a complete and whole-process fecal sludge safe disposal process,and studies the microbial response mechanism in the disposal process through applying microbiome,providing a theoretical basis for the safe reduction and harmless disposal of fecal sludge.