Coupling between thermophilic fermentation of livestock manure and thermochemical treatment of straw

Domestic large-scale biogas projects mostly use the fermentation technology at psychrophilic or mesophilic temperature, which results in low biogas production rate and large fermentor volume. And high cost for investment is the main obstacle for the advancement of biogas projects. On the other hand, straw as a common low-grade biomass in rural areas is burned at random, causing serious air pollution. Therefore, in this work, thermochemistry coupled with thermophilic fermentation was proposed to accelerate manure processing rate and promote the efficient usage of straw by burning straw to maintain the temperature for thermophilic fermentation process transformed from mesophilic fermentation. Feasibility of this coupling process was analyzed. By increasing temperature step-wisely from 30℃ to 55℃, volumetric gas production rate of pig farm biogas would increase from 1.43 m³·m^-3·d^-1 to 3.40 m³·m^-3·d^-1, and digester volume could be reduced from 1200 m³ to 500 m³. In order to maintain fermentation temperature (55℃), 339 tons of straw would be consumed every year to burn straw instead of biogas for heating.