Multiple Degradation of Rice Straw by Acclimatized Paddy Soil Microbes for Enhancement of Methane Yield in Two-Phase Liquid Anaerobic Digestion

Abstract

The hydrolysis of rice straw and swine wastewater by acclimatized paddy soil fungus for enhancing biomethane yield was investigated in two-phase liquid anaerobic digestion (L-AD). The results showed the order of impact factors on total organic carbon (TOC) and volatile fatty acid (VFA) yield was carbon/nitrogen ratio (C/Nratio)>temperature>inoculum/substance ratio (I/S ratio)>immersed height. The maximum TOC and VFA yields could be obtained after 7 days hydrolysis of rice straw under the condition of C/N ratio of 40, 37  o C, I/S ratio of 2:1, and 6.0 cm immersed height. The hydrolysis of rice straw has been terminated after 3 times hydrolysis. The cumulative CH4 production gradually increased from 54.06 mL/g VS to 177.02 mL/g VS while the retention rate declined from 75% to 45%. Considering the cost-efficiency of rice straw hydrolysis, 45% retention rate for twice degradation of rice straw were most suitable parameters for CH4 yield in two-phase L-AD.