| Co-digestion of municipal wastewater sludge with fats,oils and greases(FOG)can greatly enhance biomethane recovery in wastewater treatment facilities,but the microbial community structure of anaerobic digestion reactors is still poorly understood.High transient fat loading can lead to the accumulation of long-chain fatty acids(LCFAs)and anaerobic digestion reactor disturbances.In this study,different LCFAs additions and species were investigated to determine the optimal and inhibitory concentration levels and species,focusing on the utilization of unsaturated LCFAs in AD;in addition,the improvement effects of different process enzyme additions and species on the anaerobic digestion system that had produced inhibition were investigated,and methane yield model fitting analysis and microbial populations were performed to analyze their effects on biomethane production.The main findings were as follows:In this paper,a series of anaerobic digestion experiments comparing methane production and its fitted parameters determined that a single C18:1 prolonged the hysteresis period and ultimately showed complete inhibition.Anaerobic digestion systems operating at LCFAs levels in the concentration range of 0.5%-1.5%(v/v)increased biomethane production by up to a factor of three.The highest biomethane production was observed at 1.5% LCFAs with an extended lag period.Biomethane production was inhibited at 2% addition,and increasing the addition to 3% or would permanently inhibit biomethane production.The current study recommends running AD at approximately 1.5%(v/v)loading of LCFAs to achieve maximum yield.Comparative analysis of fitted models showed that the Modified Gompertz model is more suitable for simulating methanogenic processes with anaerobic digestion containing LCFAs with a delay period.Firmicutes,Bacteroidetes,Synergistetes,and Proteobacteria bacterial phylum were involved in the degradation of LCFA in the anaerobic reaction.At the genus level of bacteria Saccharibacteria,Anaerofilum,Syntrophomonas,Cloacibacillus play a synergistic role in promoting methane production.To avoid inhibition of the anaerobic digestion reaction during high LCFAs loading(>1.5%),microbial adaptation or addition of promoters are required to lift the inhibition.In this study,a comparative analysis between the addition of lipid hydrolase and PECI enzyme revealed that PECI enzyme could effectively alleviate the inhibition of high unsaturated LCFA concentrations.The cumulative methane production reached 1600 m L/g VS at 1.0% addition of PECIase.lipid hydrolase also had a facilitative effect but slightly less effective.the concentration of ECIase showed an increase at higher daily methane production,and the concentration of ECIase reflected the smooth proceeding of β-oxidation of LCFA.sedimentibacter Petrimonas,Clostridium XI,Cloacibacillus,and Syntrophomonas all had relative abundance in the substrate and were responsible for the hydrolysis and conversion of LCFA and VFA to methane in the substrate.The abundance of Proteobacteria and Bacteroidia can be used as indicator microbial assays to characterize the amount of VFA in the substrate by correlating the ECI enzyme concentration and methane production with the bacteriophage analysis.It is because the smooth utilization of the products after LCFA decarbonization did not cause feedback inhibition due to the accumulation of products.To compensate for the high cost of PECIase,the use of brewer’s yeast addition instead of PECIase could improve to some extent the adverse environment in the reactor caused by the accumulation of unsaturated LCFA to produce biomethane.0.5% brewer’s yeast addition was not significantly different from the effect of PECIase biomethane yield,and 0.1% was slightly less effective than PECIase.However,at 1.0% addition,brewer’s yeast did not achieve the expected promotion effect.Among them,the abundance of Phascolarctobacterium faecium and Candidatus Cloacamonas in 1.0% brewer’s yeast was associated with a significant accumulation of propionic acid. |
