Investigation On Improving Methane Production Efficiency In Anaerobic Digestion Of Several Typical Agricultural Wastes

As methane yields of agricultural wastes in anaerobic digestion are generally low,different methods were investigated on improving methane production efficiency.According to the outputs and characteristics,several typical agricultural wastes,including corn straw,chicken manure and cow manure,were used to explore how to improve methane production efficiency in this study,and the following results have been achieved.The methane yields of corn straw and cow manure were low due to their high lignocellulose content.Enzyme experiments showed that the enzyme pretreatment improved methane production efficiency through increasing reducing sugar content and oligosaccharide content,and breaking up lignocellulosic structure.Pretreated by cellulase at pH of 5.5 and temperature of 55 ? for 18 h,the methane yields of corn straw and cow manure were 188.8 mL·CH4/g·VS and 179.1 mL CH4/g·VS,increasing 28%and 12%compared with the controls respectively.However,the methane yield of corn straw only increased by 8%through hemi-cellulase pretreatment.The direct addition of amylase in anaerobic digester was easier to operate,and could increase 12%of methane yield in anaerobic digestion of corn straw.In anaerobic digestion of chicken manure,ammonia inhibition is a crucial problem on methanogens growth due to its high ammonia/ammonium content.A modified process of pre-hydrolysis-ammonia removal through membrane contactor-methanization was proposed in this study.In the pre-hydrolysis process,70%of organic nitrogen could be transformed to ammonia/ammonium.The free ammonia was removed through membrane contactor subsequently.When the total ammonia/ammonium concentration was reduced to 2 g/L,the methane yield of chicken manure was up to 437.0 mL·CH4/g·VS.The modified process was proved to be a straight forward approach to employ efficient anaerobic digestion of chicken manure which avoided ammonia inhibition,enhanced efficiency of the methanization,and recovered nitrogen as ammonium sulfate.When multiple feedstocks are available,anaerobic co-digestion might be the most economical method to utilize agricultural wastes.Anaerobic co-digestion of chicken manure and corn straw,and cow manure and corn straw were investigated,the experimental results showed that the highest methane yields were achieved at the TS ratio of 3:1.The methane yields were increased by 40%and 15%,respectively.For further improving anaerobic co-digestion efficiency of cow manure and corn straw,cellulase pretreatment of corn straw and amylase addition in digester were performed,the methane yields were up to 364.0 mL·CH4/g·VS and 377.6 mL·CH4/g·VS,increasing 103%and 111%respectively.The enzyme enhancement and co-digestion had synergistic effect on impoving methane production efficiency in anaerobic digestion.Besides,adding fruit and vegetable wastes with a ratio of 5%in the anaerobic co-digestion of cow manure and corn straw,the start-up process was more efficient and the methane yield increased by 22%.In this study,it was shown that methane production efficiency in anaerobic digestion of different agricultural waste could be improved through different methods regarding to the specific condition,in consequence,bringing in higher economic efficiency and better development of biogas project.