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.