Microbial Pretreatment Of Giant Grass For Methane Production By Anaerobic Digestion

With the consumption of traditional fossil fuels,biomass energy has gained widely attention owing to the environmental benefits.Except for the organic waste,more countries focused on the energy plants to develop biomass energy.In this paper,the anaerobic digestion?AD?and methane production performance of giant grass,an energy crop,was studied.First,the effects of harvest time on the properties and AD performance of giant grasses were studied.Second,the microbial pretreatment method was used to develop AD performance of giant grass.The impacts of pretreatment agents and oxygen amount on methane production was studied.The mechanism of pretreatment was analyzed and clarified by high-throughput 16S rRNA gene sequencing combined with the variation of parameters before and after pretreatment.The main results are as follows:Giant grasses harvested in July and December are rich in organic matter,cellulose,hemicellulose content and has a suitable C/N ratio,which are favorable conditions for AD.It was found that the giant grass harvested in July had better biochemical methane potential,and the accumulated methane yield of 267.9mL/g-VS was obtained at the organic loading of 15g-VS/L.The effects of five pretreatment agents?cow dung,sheep dung,liquid compound agent,solid agent,biogas slurry?and five oxygen flux of 0,5,10,20,40 mL/g-VS on methanogenic production of giant grass were investigated.Results are as follows:The microbial pretreatment could advance the peak of daily methane production by 1-3 day.The peak value of daily methane yield could be improved by 14.4%-75.6%?except for liquid compound agent?.The type of pretreatment agents and the amount of oxygen in the pretreatment process are important factors influencing the final pretreatment effect.In the scope of this experiment,different pretreatment agents have different responses to oxygen concentration,and the methane production can be improved well without oxygen supply during the pretreatment process.In this experiment,solid agent and liquid compound agent have better pretreatment effects,and the accumulated methane yield increasing rates range from 15.9%to 25.0%and 4.0%to 24.5%,respectively;After 25 days of digestion,the cumulative methane yield increasing rates range from 22.9%to 33.3%and26.1%to 51.1%,respectively.The relative abundance of each flora was related to the pretreatment agent type and whether oxygen was supplied during the pretreatment process.The aerobic pretreatment improved the relative abundance of aerobic bacteria,such as Acinetobacter,Pseudomonas and Citrobacter,during pretreatment process.The anaerobic pretreatment improved the relative abundance of facultative anaerobic bacteria,such as Bacillus,Lactococcus and Enterobacter,during digestion process.The relative abundance of anaerobic bacteria,such as vadinBC27 wastewater-sludge_group and Clostridium sensu stricto₁,were also improved during digestion process.The optimum concentrations of CaO,Ca?OH?2,HCl,H2SO4,NH3 and H2O2 were 2%,2%,3%,3%,4%and 5%,with the methane production increased 6.0%,8.1%,9.0%,10.4%,12.8%and 3.7%,respectively.Compared with these chemical pretreatment results,microbial pretreatment had better pretreatment effect.In this paper,the methane production of Giant grass by AD was systematically investigated,which provided a theoretical basis for the future research and application of this resource.