Rheological properties and microbial community structure in continuous dry co-digestion of corn straw and cow manure

The continuous dry co-digestion of corn straw (CS) and cow manure (CM) was studied in horizontal stainless steel push-flow reactors. The highest volumetric CH4 production of 0.76 L/(L·d) was obtained at the condition of total solid content (TS) = 25% with CM:CS = 1:2 (basis of TS). With the increase of TS content, the shear stress increased, which may be due to that the higher TS caused stronger interparticle flocculation. The viscosity increased with the enhance of proportion of CM, indicating that CM was more disadvantaged for the flow of materials than CS. When TS increased from 25% to 30%, CH4 production sharply decreased, which could be caused by the high viscosity (30 Pa·s) of the substrates, resulting in decreasing of mixing efficiency and formation of dead zones in the digester. Clostridiales and Methanosarcina were positively correlated with TS, indicating that both are more suitable for growth in dry anaerobic digestion (AD) than other microorganisms. This study provides a theoretical basis for the application of continuous AD of agricultural and rural wastes.