Comparative study of high-solid anaerobic digestion at laboratory and industrial scale - Process performance and microbial community structure

High-solid anaerobic digestion (HSD) for biogas production, compared with wet digestion, is attracting interest due to advantages such as reduced fresh water usage, improved digestate quality and potential for high organic loading rates. However, the underlying processes are not well described and evaluated for HSD. In this study, two laboratory-scale reactors (46 L) of plug-flow type were designed to simulate an industrial-scale HSD process codigesting food waste, agricultural waste and garden residues under thermophilic conditions. Performance of the laboratory-scale HSD process under stable and disturbed conditions was compared with that in industrial-scale reactors. The results showed that the laboratory- and industrial-scale processes had similar efficiency (93 %) and 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 phaseseparation or plug-flow behaviour along the horizontal axis in either laboratory- or industrial-scale reactors, indicating a need for further process optimisation. Analyses of microbial community structure showed high similarity between laboratory- and industrial-scale, but with some differences caused by downscaling. During the experiment, the laboratory- and industrial-scale processes both showed signs of disturbance, i.e. VFA accumulation at NH4+-N levels > 4 g/L, accompanied by a shift in microbial community structure at both scales, with significant increases in relative abundance of e.g. genera Defluviitoga and Methanothermobacter. In conclusion, this study confirmed the validity of simulating HSD at laboratory scale, thus providing valuable insights into biogas production from high-solid substrates, both in laboratory- and industrial-scale processes.