| Due to the dramatic social-economic growth,rapid urbanization and especially waste classification in China,the amount of food waste(FW)production has increased rapidly,which urgently needs proper treatment and disposal.Anaerobic digestion(AD)can achieve reduction and stabilization of FW and simultaneously recover sustainalble energy.However,on the one hand,anaerobic mono-digestion of FW may cause imbalance of nutrients in the system,which leads to low efficiency of methane production.On the other hand,when the organic content in the system is too high,it may cause acid inhibition,which leads to poor stability.In addition,FW has been considered as one of the important sources and hotspots of ARGs.However,the occurrence and dissemination characteristics of ARGs during the anaerobic biological treatment of FW are still unclear.Hence,enhanced strategies of anaerobic methanogenesis based on synergistic anaerobic co-digestion and activated carbon supplementation and the fate of ARGs during the process were studied.The objectives are to solve the problems of the low methanogenic efficiency,poor system stability and unclear ARGs transformation regularity in AD of FW.It is carried out in three aspects:(1)to explore the synergistic effect of methane production in FW and fruit vegetable waste(FVW)anaerobic co-digestion and its microbial mechanism;(2)to study the effects of different oil content on methanogenic efficiency and ARGs dynamics in codigestion of FW and oil and its microbial mechanism;(3)to explore the effects of activated carbon with different particle sizes on methane productivity and ARGs dynamics and its microbial mechanism under the high organic content system.The main research conclusions are as follows:1)Co-digestion of FW and FVW was employed to explore the effects of different ratios of FW: FVW on methane production and organic degradation,and the microbial community shifts were further investigated to reveal the microbial mechanism.Results showed that the FW: FVW ratio of 0.5: 0.5 showed the highest methane yield(411.2 ± 26.5 m L/g-VS),increasing by 1.2 times compared to the lowest methane yield group(FW mono-digestion).The synergistic impact of FW and FVW co-digestion caused by the continuous dissolution of organics and the continuous generation and conversion of volatile fatty acids(VFAs)was the key to the increased methane yield.The enrichment of functional bacteria involved in VFAs generation such as Proteiniphilum provided the substrates for methanogenesis continuously,thereby enhancing methane yiled.2)Co-digestion of FW and oil was conducted to investigate the impacts of different oil content on methanogenic efficiency and ARGs dynamics.The microbial community succession was further investigated to reveal the microbial mechanism.Results showed that systems with high oil content(Oil: FW 0.3: 0.7 and 0.5: 0.5)obtained higher methane yield,increasing by 3.5% and 8.0% respectively compared to the mono-digestion;but significantly prolonged the lag time of methane production(P < 0.05),extending by 9.1% and 25.3%,respectively.The microbial community structure was significantly altered in the early and final stages of AD.LCFAs-β-oxidizing bacteria(Syntrophomonas)and VFAs-degrading bacteria(Gelria)were enriched under high oil content systems,thereby enhancing the lipid degradation and methane production.Additionally,compared to the initial stage of AD,mono-digestion of FW and co-digestion of FW with oil both contributed to the elimination of ARGs.Furthermore,high lipid content significantly facilitated the reduction of ARGs(P < 0.05).The reduction of potential host bacteria was possibly responsible for the elimination of several specific ARGs,thereby affecting total ARGs profiles under high oil content systems.Therefore,potential host bacteria was the main driving factor for the transformation of ARGs.3)Two activated carbon of different particle sizes were supplemented to explore the impacts of activated carbon addition on methanogenic efficiency,system stability and ARGs dynamics under the high oraganic content system.The microbial community,functional genes and methane metabolism were analyzed to reveal the microbial mechanism.Results showed that at the ealy stage of AD,VFAs accumulated rapidly in the systems with or without activated carbon,and the total VFAs reached 8900.2-11412.8 mg/L.At that time,serious acidification occurred,which inhibited the activity of methanogen and led to the stagnation of methane production.Both granular activated carbon(GAC)and powdered activated carbon(PAC)could promote the VFAs consumption and alleviate acidification,thereby accelerating the start-up of methanogenesis and enhancing methane output.Moreover,PAC performed better than GAC.Specifically,the highest cumulative methane yield(508.1 ± 27.1 m L/g-VS)and shortest lag time(17.8 d)were observed in 5g/L PAC and 10g/L PAC group,22.0% higher and 62.5% shorter than that without activated carbon supplementation,respectively.The microbial community was remarkably altered with PAC addition.Additionally,syntrophic VFAs oxidizing bacteria(Gelria and Syntrophomonas)and direct interspecies electron transfer related microorganisms(Geobacter and Methanosarcina)were remarkably enriched by PAC.Metagenomic analysis showed that both PAC and GAC might facilitate the energy and electron transfer between microbes by acting as the electrical bridge and enhance both hydrogenotrophic and aceticlastic pathways,thus enhancing the VFAs degradation and methane production.Furthermore,the total relative abundances of ARGs were reduced during AD process.At the final stage of AD,total relative abundances of ARGs in PAC groups were significantly higher than that in control group(P < 0.05).The supplementation of PAC significantly inhibited the reductions of ARGs.Network analysis suggested that the main potential host bacteria of ARGs were Firmicutes,Bacteroidetes and Synergistetes.Moreover,the enrichment of host microorganisms with PAC addition resulted in the increased several target genes.In summary,synergistic co-digestion of FW with FVW and oil could enhance methane yield;PAC addition could effectively alleviate acidification inhibition and enhance system stability,thereby promoting methanogenesis.AD process could attribute to the elimination of ARGs.However,high lipid content and activated carbon addition could affect the ARGs dynamics.In addition,the microbial community dynamic was the main driving force affecting methane production and ARGs dynamics.This study can provide theoretical basis for enhancing the anaerobic biological treatment of FW for methane production and learning the fate of ARGs during AD process. |
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