Changes in Microbial Communities in Industrial Anaerobic Digestion of Dairy Manure Caused by Caldicellulosiruptor Pretreatment

Extremophilic biological process (EBP) pretreatment increases substrate availability in anaerobic digestion, but the effect on downstream microbial community composition in industrial systems is not characterized. Changes in microbial communities were determined at an industrial facility processing dairy manure in a modified split-stream system with three reactor types: 1) EBP tanks at 70-72C, 2) mesophilic Continuously Stirred Tank Reactors (CSTRs), and 3) mesophilic Induced Bed Reactors (IBRs) receiving combined CSTR and EBP effluent. All reactors had a two-day hydraulic retention time. Samples were collected weekly for 60 days. pH, volatile fatty acid and bicarbonate concentrations, COD, and methane yield were measured to assess tank environmental conditions. Microbial community compositions were obtained via 16S rRNA gene sequencing. EBP pretreatment increased acetate availability but led to a decline in the relative abundance of acetoclastic Methanosarcina species in downstream IBRs. Rather, syntrophic methanogens, e.g., members of Methanobacteriaceae, increased in relative abundance and be-came central to microbial co-occurrence networks, particularly in association with hydrogen-producing bacteria. Network analysis also demonstrated that these syntrophic relationships were tightly coordinated in pretreated digestate but absent in the untreated CSTRs. By promoting syntrophic methanogenesis while increasing acetate concentrations, EBP pretreatment requires system configurations that enable acetoclast retention to prevent acetate underutilization and maximize methane yields.

极端嗜热生物过程（Extremophilic Biological Process, EBP）预处理可提升厌氧消化过程中的底物可用性，但目前尚未明确其对工业厌氧消化系统下游微生物群落组成的影响。本研究在一处处理奶牛粪便的工业设施中开展，该设施采用改良分流式系统，包含三类反应器：1）运行温度为70~72℃的EBP反应罐；2）中温连续搅拌釜式反应器（Continuously Stirred Tank Reactors, CSTRs）；3）接收连续搅拌釜式反应器与EBP反应罐混合出水的中温诱导床反应器（Induced Bed Reactors, IBRs）。所有反应器的水力停留时间均为2天。研究周期共计60天，每周采集一次样品；通过测定pH值、挥发性脂肪酸（Volatile Fatty Acid, VFA）与碳酸氢盐浓度、化学需氧量（Chemical Oxygen Demand, COD）以及甲烷产率，以评估各反应罐的运行环境状况；同时借助16S rRNA基因测序技术获取微生物群落组成信息。结果显示，EBP预处理提升了乙酸盐的可利用性，但导致下游诱导床反应器中乙酸营养型甲烷八叠球菌（acetoclastic Methanosarcina）的相对丰度下降。取而代之的是，互营养型产甲烷菌（例如甲烷杆菌科（Methanobacteriaceae）成员）的相对丰度显著提升，并成为微生物共现网络的核心类群，尤其与产氢细菌形成紧密的协同关联。网络分析进一步表明，这类互营养关系在经过预处理的消化液中紧密协调，但在未经过预处理的连续搅拌釜式反应器中并未出现。综上，EBP预处理在促进互营养型产甲烷作用并提升乙酸盐浓度的同时，需要配置能够保留乙酸营养型微生物的系统结构，以避免乙酸盐未被充分利用，进而最大化甲烷产率。