Li Lei, He Qin, Ma Yao, Wang Xiaoming, Peng Xuya
Key Laboratory of Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing University, Chongqing, 400045, China.
Microb Cell Fact. 2016 Apr 25;15:65. doi: 10.1186/s12934-016-0466-y.
Anaerobic digesters become unstable when operated at a high organi c loading rate (OLR). Investigating the microbial community response to OLR disturbance is helpful for achieving efficient and stable process operation. However, previous studies have only focused on community succession during different process stages. How does community succession influence process stability? Is this kind of succession resilient? Are any key microbial indicator closely related to process stability? Such relationships between microbial communities and process stability are poorly understood.
In this study, a mesophilic anaerobic digester for treating food waste (FW) was operated to study the microbial diversity and dynamicity due to OLR disturbance. Overloading resulted in proliferation of acidogenic bacteria, and the resulting high volatile fatty acid (VFA) yield triggered an abundance of acetogenic bacteria. However, the abundance and metabolic efficiency of hydrogenotrophic methanogens decreased after disturbance, and as a consequence, methanogens and acetogenic bacteria could not efficiently complete the syntrophy. This stress induced the proliferation of homoacetogens as alternative hydrogenotrophs for converting excessive H2 to acetate. However, the susceptible Methanothrix species also failed to degrade the excessive acetate. This metabolic imbalance finally led to process deterioration. After process recovery, the digester gradually returned to its original operational conditions, reached close to its original performance, and the microbial community profile achieved a new steady-state. Interestingly, the abundance of Syntrophomonas and Treponema increased during the deteriorative stage and rebounded after disturbance, suggesting they were resilient groups.
Acidogenic bacteria showed high functional redundancy, rapidly adapted to the increased OLR, and shaped new microbial community profiles. The genera Syntrophomonas and Treponema were resilient groups. This observation provides insight into the key microbial indicator that are closely related to process stability. Moreover, the succession of methanogens during the disturbance phase was unsuitable for the metabolic function needed at high OLR. This contradiction resulted in process deterioration. Thus, methanogenesis is the main step that interferes with the stable operation of digesters at high OLR. Further studies on identifying and breeding high-efficiency methanogens may be helpful for breaking the technical bottleneck of process instability and achieving stable operation under high OLR.
厌氧消化器在高有机负荷率（OLR）下运行时会变得不稳定。研究微生物群落对OLR干扰的响应有助于实现高效稳定的工艺运行。然而，以往的研究仅关注不同工艺阶段的群落演替。群落演替如何影响工艺稳定性？这种演替具有恢复力吗？是否有任何关键微生物指标与工艺稳定性密切相关？微生物群落与工艺稳定性之间的这种关系尚不清楚。
在本研究中，运行一个中温厌氧消化器来处理食物垃圾（FW），以研究由于OLR干扰导致的微生物多样性和动态变化。过载导致产酸菌增殖，产生的高挥发性脂肪酸（VFA）产量引发了大量产乙酸菌的出现。然而，干扰后氢营养型产甲烷菌的丰度和代谢效率下降，结果，产甲烷菌和产乙酸菌无法有效地完成互营代谢。这种压力促使同型产乙酸菌增殖，作为将过量H2转化为乙酸盐的替代氢营养菌。然而，易受影响的甲烷丝状菌也未能降解过量的乙酸盐。这种代谢失衡最终导致工艺恶化。工艺恢复后，消化器逐渐恢复到原来的运行条件，接近其原来的性能，微生物群落概况达到一个新的稳态。有趣的是，互营单胞菌属和密螺旋体属的丰度在恶化阶段增加，并在干扰后反弹，表明它们是具有恢复力的菌群。
产酸菌表现出高度的功能冗余，能迅速适应增加的OLR，并形成新的微生物群落概况。互营单胞菌属和密螺旋体属是具有恢复力的菌群。这一观察结果为与工艺稳定性密切相关的关键微生物指标提供了见解。此外，在干扰阶段产甲烷菌的演替不适合高OLR下所需的代谢功能。这种矛盾导致了工艺恶化。因此，产甲烷作用是干扰消化器在高OLR下稳定运行的主要步骤。进一步研究鉴定和培育高效产甲烷菌可能有助于突破工艺不稳定的技术瓶颈，并在高OLR下实现稳定运行。
