外源添加剂对黄贮小麦秸秆产甲烷潜力及微生物群落的影响

Effects of yellow silage additives on methane production and microbial community dynamics during anaerobic digestion of wheat straw

为探讨添加不同外源添加剂对黄贮小麦秸秆产甲烷潜力和微生物群落结构的影响,该研究以小麦秸秆为黄贮原料,添加乙酸(3‰ACE组)和异型发酵乳酸菌复合系(3‰MI1组,6‰MI2组),调整含水率至50%,黄贮65 d后,以黄贮小麦秸秆为厌氧发酵原料,探究发酵过程中的指标性质和微生物群落结构。研究发现黄贮预处理后,发酵系统中的初始挥发性有机酸中的乳酸和乙酸增加、甲烷含量增加、可溶性化学需氧量(sCOD)增加。添加了外源添加剂的ACE组、MI1组、MI2组的累积甲烷产量较干黄小麦秸秆(WS组)提高了4.7%~10.6%,而未添加添加剂的CK组的累积甲烷产量较WS组降低了9%。发酵系统中的主要优势细菌为Bacteroidetes、Firmicutes和Proteobacteria,优势古菌为甲烷鬃菌属Methanosaeta,黄贮预处理改变了发酵系统微生物的群落结构,促进了小麦秸秆的甲烷转化,为木质纤维素的沼气转化提供参考。

Straw-biogas-fertilizer has become one of the promoted utilization modes for the agricultural waste,particularly on large amount of crop straw that produced annually in China.However,a long-term storage of straw has posed a great problem on a straw biogas plant.A commonly used method,the yellow silage,can be expected to preserve nutrient,while reduce the dry matter loss of straw during storage.This study aims to explore the effects of yellow silage additives on methane production and microbial community dynamics during anaerobic digestion of wheat straw.The experiment was divided into two parts:yellow silage and anaerobic digestion.Yellow silage treatments were inoculated additives into the dry yellow wheat straw with a moisture content of 50%for 65 days,including CK group(without additives),ACE group(acetic acid addition of 3‰),MI1 group(lactic acid bacteria community addition of 3‰),MI2 group(lactic acid bacteria community addition of 6‰).The results showed that the pH of four groups below 4.7,indicating excellent fermentation quality.Hemicellulose and cellulose decreased during yellow silage,especially CK group only 22.2%and 31.8%,respectively.In the treatment with additives,the hemicellulose and cellulose content were significantly higher than that in the CK group,indicating that the addition of additives was helpful to preserve available nutrients.In the anaerobic digestion experiment,the raw materials were the yellow silage wheat straw(CK,ACE,MI1,MI2 group)and dry yellow wheat straw(WS group).The batch tests were conducted for up to 20 days at(36±2)℃.The working volume of each reactor was 300 mL,consisting of 12 g(TS)inoculum and 3 g(TS)substrate,with a TS content of 5%and the remaining space filled with nitrogen gas.Inoculum without any added feedstock was used as a blank.Triplicate reactors were run for each treatment.The biogas production and methane composition were measured every day,whereas,the pH value,volatile fatty acids(VFA),soluble chemical oxygen demand(s COD)were measured during anaerobic digestion.High-throughput sequencing was used to determine the microbial community structure on the twentieth day of anaerobic digestion,in order to detect the effect of yellow silage pretreatment on the bacteria and archaea community in anaerobic fermentation system.The results from the anaerobic experiment showed that the VFA concentration and s COD increased significantly in yellow silage group at the initial stage,where mainly VFA in the fermentation system were lactic acid and acetic acid.As the fermentation time increased,the VFA concentration and s COD decreased after 2 days fermentation,where the propionic acid was the main component of VFA.The cumulative methane yield of ACE group,MI1 group,MI2 group were 213.7,202.2,207.9 mL/g,increased by 10.6%,4.7%and 7.6%,respectively,compared with WS group(193.2 mL/g),while CK group were 175.8 mL/g,decreased by 9.0%compared with WS group.After anaerobic digestion,the main bacteria were Bacteroidetes,Firmicutes,Proteobacteria,while the main archaea were Methanosaeta,indicating that the yellow silage can affect the microbial structure in the fermentation system.This finding can provide an important theoretical and technical support for energy conversion of crop straw in large-scale biogas production.