初始发酵pH对秸秆酒精醪液沼气发酵及其系统内微生物群落的影响

目的]探究初始pH对秸秆酒精醪液厌氧发酵产甲烷的影响。方法]利用秸秆酒精醪液作为唯一发酵底物,并将初始发酵pH分别设置为4.0、5.0、6.0、6.5、7.0、7.5、8.0,8.5,采用序批式厌氧发酵30 d。结果]在150 mL的发酵体积下最终的甲烷积累量依次为17、24、227、289、246、257、234和143 mL。当初始发酵pH升高时,发酵液中残留的挥发性脂肪酸(VFA)中的乙酸所占比例逐渐升高,pH为5.0时乙酸占12.8%,pH为8.5时乙酸占43.9%。通过比较初始pH为4.0、6.5和8.5时,VFAs在发酵过程中的动态变化,发现初始pH为6.5时,乙酸的含量在第1.5天达到峰值,为3 753.6 mg/L占总量71.6%,最终乙酸被减少了72.4%;初始pH为8.5时,乙酸的含量在第10天时增至峰值,为1 322.9 mg/L(53.8%),最终乙酸减少了36.0%。初始pH为4.0时,VFAs的总量和组成都没有明显的变化。当初始发酵pH为6.0、6.5、7.0、7.5时,发酵系统内的优势细菌为梭菌属(Clostridium),相对丰度为40%~47%;优势古菌为甲烷八叠球菌属(Methanosarcina)和甲烷鬃毛菌属(Methanosaeta),其相对丰度之和为85%~88%。当初始pH为8.5时,系统内的优势细菌为普雷沃式菌(Prevotella)和互养单胞菌属(Syntrophomonas),相对丰度分别为36.8%和14.7%;优势古菌为甲烷杆菌属(Methanobacterium)和甲烷热杆菌属(Methanothermobacter),在其全古菌序列中分别占62.3%和11.4%。结论]当初始发酵pH为6.5时,甲烷的产气积累量最高;当初始发酵pH为6.0、6.5、7.0、7.5时,为乙酸营养型型甲烷发酵;当初始pH为8.0和8.5时,为氢营养型甲烷发酵。

Effect of Initial pH on Methane Production from Waste Liquor of Alcohol from Stalk and Microbial Community

Objective]Exploring the impact of initial pH on anaerobic fermentative production of methane from waste liquor of alcohol from stalk.Method]As the waste liquor of alcohol from stalk was the only fermentation substrate, sequencing batch reactor was utilized for 30 days when the initial pH was 4.0,5.0,6.0,6.5,7.0,7.5,8.0,8.5 respectively.Result]In the fermentation volume of 150 mL, the final methane accumulates to 17,24,227,289,246,257,234 and 143 mL respectively.When the initial pH was rising, the proportion of acetic acid in VFAs-volatile fatty acids remaining fermentation liquor was also increasing.Acetic acid was 12.8% in proportion when pH was 5.0 and acetic acid is 43.9% in proportion when pH was 8.5.Comparing the dynamic changes of VFAs during fermentation when the initial pH was 4.0,6.5 and 8.5, it turned out that the content of acetic acid reaches to the peak-3 753.6 mg/L (71.6% of the total amount) 1.5 days later,and the final consumption of acetic acid was 72.4% when the initial pH was 6.5.Moreover, when the initial pH was 8.5, content of acetic acid reaches to the peak-1 322.9 mg/L (53.8% of the total amount) 10 days later,and the final consumption of acetic acid was 36%.There was no obvious change of the total amount or composition of VFAs when the initial pH was 4.0.When the initial pH was 6.0,6.5,7.0,7.5, the dominant bacteria was Clostridium in fermentation system, and the relative abundance was 40%-47%;dominant archaeal was Methanosarcina and Methanosaeta, and the relative abundance was 85%-88%.However, the dominant bacteria was Prevotella and Syntrophomonas in fermentation system, and the relative abundance was 36.8% and 14.7% respectively;dominant archaeal was Methanobacterium and Methanothermobacter, and the relative abundance was 62.3% and 11.4% respectively when the initial pH was 8.5.Conclusion]The gas from methane accumulates to the highest when the initial pH is 6.5;the dominating methanogenic substrates are acetate when the initial pH is 6.0,6.5,7.0 and 7.5;the dominating methanogenic substrates are H2-CO2 when the initial pH is 8.0 and 8.5.