Feasibility study of a centralized biogas plant performance in a dairy farming area

In this feasibility study, the anaerobic co-digestion of different organic wastes obtained from a dairy farming area in Hokkaido prefecture, Japan was investigated with the objective of building a centralized biogas plant. The daily organic wastes generated from the study area were 210 t/day, comprised of 90% barn wastes and 10% wastewater sludge and feed residue of total mixed ration. The wastes can be categorized into high VS/TS ratio which is easily biodegradable and low VS/TS ratio which is hardly biodegradable. The methane yield of each substrate was investigated in a batch experiment followed by a continuous experiment at mesophilic temperature. Compared to other organic wastes, higher methane production potential were obtained from dairy manures with the highest yield, resulting in 0.19 m³/kgVS, from dairy manure slurry. Moreover, a longer hydrolysis rate constant (7.2 days) was observed with dairy manure slurry rather than beef cattle manure (3.4 days). Due to the mixture of substrates in the continuous experiment, the methane yield increased significantly (0.35 m³/kgVS), reaching almost double of that observed during batch experiments. The average biogas production performance was 39.26 m³ per m³ of added substrate. This illustrates the potential economic viability of the prospective centralized biogas plant.