分层接种对猪粪厌氧干发酵产气性能及微生物群落结构的影响

为避免厌氧干发酵酸抑制,提高产气效率,以猪粪和玉米秸秆为发酵原料,采用中温批式试验,在总固体(Total Solid,TS)为20%、接种比为25%的条件下研究分层接种和混合接种对猪粪干发酵厌氧消化性能的影响。结果表明:2种接种方式下的发酵体系内挥发性脂肪酸(Volatile Fatty Acids, VFAs)均发生明显积累,其中,分层接种在第15天的TVFAs质量浓度达到33.0mg/g,之后明显降低,至发酵结束时VFAs消耗殆尽。混合接种从第15天至发酵结束,TVFAs质量浓度维持在29.2～38.5 mg/g高水平范围内。分层接种的累积挥发性固体甲烷产率为211.5 mL/g。高通量测序结果显示,氢营养型产甲烷途径在2种接种方式下均占主导,但分层接种增加了发酵体系中微生物的丰富度和多样性,且群落结构更加稳定。进一步分析表明,乙酸和pH值是影响厌氧干发酵中微生态结构的主要环境因子。该研究结果为解除畜禽养殖废弃物酸抑制、提高产气效率提供理论依据与有益借鉴。

Influences of layer inoculation on biogas production and microbial community in solid-state anaerobic fermentation of pig manure

China is a large agricultural country, livestock manure is both agricultural waste and resources. Among the many treatment processes, solid-state anaerobic digestion (SS-AD) to produce biogas is one of the effective measures to realize its resource utilization and solve environmental pollution. While high total solid (TS) content causing a reduction of methane yields or failure of digestion process because the accumulation of volatile fatty acids (VFAs) resulted in the inhibition of methanogens. At present, the research on volatile fatty acids (VFAs) mainly focuses on the aspects of co-substrate for digestion, leachate recirculation and external buffer material to increase biogas production. The inoculum has an important impact on the tolerance of intermediate metabolites and the start-up time of anaerobic fermentation. Previous research mainly focuses on microbial acclimation and feedstock/inoculum (F/I) ratio under the premixing inoculation method (fermentation after mixing the inoculum and substrate), while the exploration of different inoculation methods for SS-AD and the correlation between the dynamic changes of microbial community structure and metabolites (such as VFAs) need to be studied in depth. In this paper, the biogas production performance and micro-ecological succession law of pig manure and maize straw in layer inoculation and premixing inoculation fermentation were compared. A pilot-scale laboratory experiment was performed in a self-made vertical plexiglass reactor with a total volume of 11 L under feedstock/inoculum ratio=25% in SS-AD process (TS=20%). The result showed that, the first peak of TVFAs mass concentration in layer inoculation system reached 33.0 mg/g on the day 15, and had a greater decline until the end of fermentation. The mass concentration of TVFAs in premixing inoculation system was varied in the range of 29.2-38.5 mg/g on days 15-78. The cumulative specific methane yield (SMY) of layer inoculation fermentation reached 211.5 mL/g is the highest. CH4 yield in layer inoculation system was mucher higher than in premixing inoculation even with the same substrate, which indicated that layer inoculation can lead to the comsuption of VFAs over time, make the process run effectively, and reduce the startup time. The SMY of premixing inoculation was under 1.0 mL/g-VS during the whole experiment. In layer inoculation system, the biogas CH4 content ranged from 54.0% to 66.0% after day 20. The CH4 content in premixing inoculation fermentation showed a rapid increase after 52 days of digestion and reached 58.1% on day 78. High-throughput sequencing results showed that hydrogenotrophic methanogen was the dominant methane production pathway during SS-AD of different inoculation methods. Layer inoculation can increase the richness and diversity of microorganisms in the fermentation system, and the community structure is more stable than premixing inoculation. The results of cluster analysis on microbial diversity showed that the difference both layer inoculation and premixing inoculation system showed good similarity in the bacteria and archaea samples of stage I~II and stage III~IV. Further analysis showed that the main environmental factor affecting layer inoculation and premixing inoculation are acetic acid and pH, respectively. The results of this study provide a scientific basis for alleviating the VFAs inhibition of SS-AD of livestock and poultry farming waste and increasing methane yield.