Enhanced Anaerobic Digestion Of Straw Lignocellulose Via Ruminal Microbiota And Digestate Post-treatment

China is a country that generates a large amount of agricultural straw each year.At the moment,crop residue burning is one of the main disposal methods.The irrational disposal methods not only waste resources,but also cause serious environmental pollution.Anaerobic digestion can convert straw into biogas energy and organic fertilizer.However,the unique physical and chemical structure of straw makes lignocellulosic hydrolysis difficult,which is also the main technical barrier to anaerobic digestion.Firstly,the ruminal microbiota was used to improve the anaerobic digestion of straw lignocellulose in this study.Studied by the biogas yield,methane yield,degradation efficiencies of lignocellulose,high-throughput sequencing and quantitative real time polymerase chain reaction,the ruminal microbiota can enhance the anaerobic efficiency during the process of increasing the organic loading in horizontal reactor,but the biogas residue still contains some lignocellulose which has the potential of methane.Then the methane potential of biogas residue was improved by Phanerochaete chrysosporium and thermal-alkaline post-treatment.Finally,straw and biogas residue were used as substrates for cooperative digestion.To achieve deep utilization of straw and biogas residue,the study analysed anaerobic parameters,humic acid and metal ion was by gradually increasing the organic loading in horizontal reactor.The research results were as follows:(1)Straw was used as a substrate for anaerobic digestion in the co-inoculated system of ruminal microbiota and anaerobic sludge.The efficiency of anaerobic digestion was stable and the biogas yield and methane yield were maintained at about 450 and 245 m L/g VS when the organic loading was 1.29～4.31 g VS/(L·d).The degradation efficiencies of cellulose,hemicellulose and lignin were 71.4%,92.8% and 14.8%,respectively.Under high organic loading(5.61 g VS/(L·d)),the degradation efficiencies of cellulose and hemicellulose decreased by 23.8% and 36.7% which might be due to the inhibition of hydrolase activity by the accumulation of humic acid.The relative abundance of Ruminococcus,Fibrobacter,Prevotella,Syntrophomonas and Marinilabiliaceae increased during the stable operation stage,as does the gene copy variation of the GH5,GH48,GH10,and GH11.The results of high-throughput sequencing of archaea showed that Methanosarcina became the main methanogens with the increase of organic loading.(2)Phanerochaete chrysosporium and thermal-alkaline post-treatment were used to improve methane potential of biogas residue.During the process of Phanerochaete chrysosporium post-treatment,the degradation of lignocellulose occurred primarily between14 and 21 days and the degradation efficiencies of cellulose was higher than lignin.However,the degradation efficiencies of cellulose by thermal-alkaline post-treatment was lower than lignin.The experiment of biochemical methane potential showed that the highest methane yield(116.2 m L/g VS)of Phanerochaete chrysosporium was achieved when the inoculation amount was 10% and the time was 14 days.The optimal methane yield(134.7 m L/g VS)was achieved in the experimental group with the alkaline dosage of 60 mg/g which was 1.45 times higher than the blank group(substrate without post-treatment).Furthermore,thermal-alkaline post-treatment also can improve the methane production intensity of the entire straw anaerobic process.(3)The biogas residue and straw were co-digested in a system with ruminal microbiota and anaerobic sludge.The anaerobic efficiency of the co-digestion system was improved under the same straw organic loading.When compared to single digestion,biogas and methane production increased by 33% and 35% under high organic loading(5.61 g VS/(L·d)).Available metal ions brought by biogas residue after thermal-alkaline post-treatment bind to carboxyl on humic acid preferentially and reduce the adsorbability and complexation of humic acid.Under high organic loading,the composition of dominant microorganism was similar between co-digested and single-digested system,but the relative abundance of microorganism changed.