Comparative study of high-solid anaerobic digestion in lab- and industrial-scale; microbial community structure

High-solid anaerobic digestion (HSD) for biogas production, is attracting interest due to advantages such as reduced fresh water usage, improved digestate quality and potential for high organic loading rates. However, in comparison to wet anaerobic digestion these processes are less described and evaluated. In the current study two lab-scale reactors (45 L) of plug-flow type were designed to simulate an industrial-scale high-solid digestion process, co-digesting food waste, agricultural and garden residues at thermophilic conditions. The main aim was to investigate how well the performance of a lab-scale HSD process represent what is obtained in a full-scale plant during both stable and disturbed conditions. The results showed that the lab- and industrial-scale reactors had similar process efficiency (93%), VS reduction (43% and 41% respectively) and relatively similar specific methane production (339 and 366 NL CH4/kg VS respectively). Results from tracer studies combined with chemical analyses showed no phase-separation or plug-flow behaviour along the horizontal axis in either lab- or industrial-scale reactors, indicating a need for further optimization. Analyses of microbial community structure showed high similarity between lab- and industrial-scale, but with some differences caused by the down-scaling. During the time of the experiment both lab- and industrial-scale processes showed signs of disturbance, i.e. VFA accumulation at NH4+-N levels >4 g/L. During this disturbance a shift in the community structure was observed in both scales, with significant increase in relative abundance of e.g. genera Defluviitoga and Methanothermobacter. In conclusion, this study demonstrates the viability of simulating HSD at lab-scale, thus providing valuable insights for biogas production from high-solid substrates, both in lab- and full-scale processes.

用于沼气生产的高固体厌氧消化（High-solid anaerobic digestion, HSD），凭借减少淡水消耗、优化沼渣品质以及实现高有机负荷率的潜力等优势，日益受到学界与工业界的关注。然而，相较于湿式厌氧消化工艺，此类高固体厌氧消化过程的相关研究与评估仍相对不足。本研究搭建了两台容积为45升的推流式实验室规模反应器，用于模拟工业规模的高固体厌氧消化工艺，在嗜热条件下共消化餐厨垃圾、农业及园林废弃物。本研究的核心目标为探究实验室规模高固体厌氧消化工艺的运行表现，在稳定与扰动工况下，与工业规模装置的实际运行效果的匹配度。研究结果表明，实验室与工业规模反应器的工艺效率相近（93%），挥发性固体（Volatile Solids, VS）去除率分别为43%与41%，单位甲烷产率也较为接近（分别为339与366 NL CH₄/kg VS）。示踪剂研究结合化学分析结果显示，无论实验室还是工业规模反应器，其沿水平轴向均未出现相分离或推流行为，这提示该工艺仍存在进一步优化的空间。微生物群落结构分析显示，实验室与工业规模装置的群落结构整体高度相似，但因缩尺效应存在部分特异性差异。实验期间，两类规模的工艺均出现了运行扰动迹象：当氨氮（NH₄⁺-N）浓度高于4 g/L时，发生了挥发性脂肪酸（Volatile Fatty Acid, VFA）积累。在此扰动工况下，两类规模的反应器群落结构均发生了显著转变，例如德弗利氏菌属（Defluviitoga）与甲烷嗜热杆菌属（Methanothermobacter）的相对丰度均出现明显提升。综上，本研究证实了实验室规模模拟高固体厌氧消化工艺的可行性，可为实验室及工业规模的高固体底物沼气生产工艺提供极具价值的参考依据。