Study On Anaerobic Digestion Of Vegetable Waste Pretreated With A Microbial Consortium Of Degrading Lignocellulose

Vegetable from the process of harvest to final consumption,which will produce a large number of vegetable waste,and the characteristics of high moisture content and high organic matter content are suitable for anaerobic digestion.Vegetable waste contains some refractory lignocellulose,which will cause problems such as incomplete utilization of raw materials,difficult discharge and easy formation of scum during anaerobic digestion.Therefore,it is very important to pretreat vegetable waste.The physical and chemical methods have the problems of high energy consumption,easy to produce inhibitory substances and excessive pretreatment.But biological pretreatment can effectively avoid the above problems.In this study,the basic anaerobic digestion parameters of the vegetable waste that were not pretreated were first studied.The total solid was set to 4% and 8%,and three inoculation ratios of 0.8,1.0 and 1.2 were set at each solid content for batch anaerobic digestion.According to the results,the cumulative methane production increased with the increase of solid content and decreased with the increase of inoculation ratio.When the solid content was 8% and the inoculation ratio was 0.8,the cumulative methane production was the largest,reaching 253.81 m L·g-1VS.At the same time,it was found that the higher the inoculation ratio was,the shorter the anaerobic digestion time was,but the lower the cumulative methane production was.When the inoculation ratio was unchanged,the higher the solids content was,the longer the delay period was,and the higher the cumulative methane production was.The degradation rate of propionic acid was higher when the inoculation ratio was lower and the inoculation ratio was higher.After determining the basic process parameters of anaerobic digestion of vegetable waste,in order to further improve the energy conversion rate of raw materials,a microbial consortium of degrading lignocellulose were selected for pretreatment,and biochar and trace elements were added.The effects of pretreatment time(24 h?48 h?72 h),biochar addition ratio(5%?15%?20%)and trace element addition amount(10 m L·L-1?20 m L·L-1?40 m L·L-1)on methane production were studied by orthogonal experiment.And the optimum pretreatment time was 24 h.The optimum addition ratio of biochar was 20% of the total solid,and the optimum addition ratio of trace element solution was 40 m L·L-1(Fe Cl2·4H2O: 20 mg·L-1?Co Cl6·6H2O: 2 mg·L-1?Ni Cl6·6H2O: 2 mg·L-1).The biogas production increased with the increase of biochar addition ratio and with the increase of trace element addition,but with the increase of pretreatment time,the biogas production decreased.Finally,in order to determine the organic load suitable for continuous anaerobic digestion of vegetable waste and make the system run efficiently and stably under this load.The effects of adding biochar and trace elements on the continuous anaerobic digestion of pretreated vegetable waste were studied,and the microbial community structure during the continuous anaerobic digestion of vegetable waste was analyzed.The results showed that the pretreatment and addition of biochar significantly promoted methane production under OLR 1.5~3.0a g·VS·L-1·d-1 and 3.0b~3.25 g·VS·L-1·d-1.When the OLR was 3.0 g·VS·L-1·d-1,it is most suitable for the operation of continuous anaerobic digestion of vegetable waste.The addition of biochar reduced the accumulation rate of volatile fatty acids and improved the buffering capacity of the anaerobic digestive system.When the concentration of volatile fatty acids was below 4000 mg·L-1,the addition of trace elements can obviously promote the transformation of volatile fatty acids,but there is no obvious effect on the control of trace elements for a short time after the concentration of volatile fatty acids exceeded 7000 mg·L-1.Combined with the Shannon index of bacteria and archaea,it is concluded that the diversity of bacterial community structure was higher than that of archaea during anaerobic digestion.The pretreatment improved the archaea community structure diversity,and biochar significantly increased the bacterial and archaea community structure diversity.Bacteroidetes and Firmicutes were the dominant bacteria in the bacterial community throughout the anaerobic digestion process.Methanosaeta always dominated in the archaea community,and the relative abundance remained above 50%.At OLR 3.0a g·VS·L-1·d-1,pretreatment and biochar addition both promoted the production of Candidatus Methanofastidiosum.Under OLR 4.0 g·VS·L-1·d-1,biochar can induce the production of Methanosarcina.