启动模式对水稻秸秆厌氧发酵稳定性及产气效率的影响

Effects of Startup Modes on Stability and Biogas Production During Anaerobic Mesophilic Fermentation of Rice Straw

秸秆厌氧发酵是实现农业废弃物能源化利用,支撑农业固碳减排的重要途径。但是,秸秆的高负荷发酵通常会导致系统酸化,影响发酵稳定性。研究以驯化的厌氧污泥为接种物,在不同物料浓度(5%、7%和9%TS)下,研究了一步启动(OSS, one-step startup)和逐级提升启动(SIS, stepwise-increasing startup)两种模式对秸秆中温(35℃)厌氧发酵效率及稳定性的影响。结果表明,两种启动模式均可正常启动秸秆厌氧发酵过程,水解阶段OSS组趋向于丙酸型发酵,但SIS组可维持稳定的乙酸型发酵,丙酸和乙酸降解效率高,挥发性脂肪酸最高累积浓度仅为OSS组的18.4%~40.3%。56 d发酵过程中,所有实验组均稳定产甲烷;与OSS组相比,逐级提升启动对较低物料浓度(5%和7%TS)的产气率无显著影响,但9%TS实验组的TS产气率显著提升。高通量测序结果显示,Sphaerochaeta,Proteiniphilum和Bacteroidales是OSS组中的优势细菌,vadinBC27 wastewater-sludge group和Synergistaceae是SIS组的优势细菌;氢营养型产甲烷菌Methanoculleus秸秆厌氧消化过程中的优势古菌,SIS组存在较高丰度的的脂肪酸互营氧化菌和氢营养型产甲烷菌Methanobacterium,有利于促进VFAs降解产甲烷。因此,启动方式对秸秆发酵性能和微生物群落结构具有明显的影响,逐级提升启动可以有效缓解高浓度秸秆发酵过程中的VFAs累积,有利于预防厌氧消化系统酸化,维持系统稳定并提高产气率。

Straw anaerobic digestion is an important way to achieve the energy utilization of agricultural wastes and support agricultural carbon sequestration and emission reduction. However, high-load fermentation of straw often leads to acidification, which would affect fermentation stability of anaerobic fermentation process. In this study, we analyzed the effects of one-step startup(OSS) and stepwise-increasing startup(SIS) on the efficiency and stability of mesophilic(35℃) anaerobic digestion of rice straw, with different total solids concentrations(5%, 7% and 9% TS). The domesticated anaerobic sludge was used as inoculum. Results showed that both modes could start the anaerobic digestion of rice straw normally. In the hydrolysis stage, the OSS group tended to propionate-type fermentation, while the SIS group could maintain stable acetate-type fermentation with a higher propionate degradation rate, and the highest cumulative concentration of volatile fatty acids was only 18.4%~40.3% of the OSS group. During the 56-day fermentation, all groups produced methane stably. Compared with the OSS group, the SIS had no significant effect on the biogas yield of lower TS groups(5% and 7% TS), but had a significant improvement on TS biogas yield of 9% TS group. High-throughput sequencing results showed that Sphaerochaeta, Proteiniphilum and Bacteroidales were the dominant bacteria of OSS groups, while vadinBC27 wastewater-sludge group and Synergistaceae dominated in the bacterial communities of SIS groups. In addition, hydrogenotrophic methanogen Methanoculleus was the most dominant archaea during the anaerobic digestion of rice straws. In SIS group, the presence of relatively abundant syntrophic VFA-oxidizing bacteria and hydrogenotrophic methanogen Metanobacterium was beneficial to promote the degradation of VFA and methanogenesis. Therefore, the startup mode had a significant impact on performance and microbial community structure of anaerobic digestion of rice straws. The stepwise-increasing startup could effectively alleviate the accumulation of VFAs in the process of high load anaerobic digestion of rice straws, which was conducive to preventing acidification, maintaining process stability and improving biogas production rate.