Biogas production by psychrophilic anaerobic digestion and biogas-to-hydrogen through methane reforming: experimental study and process simulation

This research investigated the early stage of the culture’s adaptation during psychrophilic anaerobic digestion (20ﾟC) of complex substrates (dairy manure and grass silage) at increasing organic loading rate (OLR; 1-5 g VS/L.d) and total solids content (TS; 7-10%) in batch reactors. The methane yield from mono-digestion of dairy manure was higher at lower OLRs, while in co-digestion of the dairy manure and grass silage, the trend was the opposite. Similarly, the reactors with lower TS content showed higher methane yield in mono-digestion of dairy manure. Introducing grass silage to the bioreactors enhanced the methane yield in all experiments. The substrate degradation by inoculum was confirmed by three kinetic models (first-order, Cone, and modified-Gompertz). The microbiome analysis revealed that the Bacteroidetes phylum was dominant, indicating the inoculum’s capability to degrade and ferment the organic matter in the complex substrates. An integrated psychrophilic anaerobic digestion with a dry methane reforming plant for green hydrogen production was rigorously simulated using Aspen Plus V11. The results indicated that 48.07 kg/h biogas could produce 8.11 kg/h hydrogen. In addition, the proposed process reduced the CO₂ emission by 398,736 tonnes/year compared to the direct use of biogas for electricity production. The current research provides an assessment of the on-farm biogas plants potential in cold environments. In addition, the developed process simulation platform could be employed to design and optimize the biogas plants