Hydrolytic Acidification of Rice Straw by Domesticated Paddy Soil Microbes for Methane Yield Via Liquid Anaerobic Digestion

Abstract

This study aimed to investigate the optimal controlling strategy for hydrolytic acidification (HA) of rice straw (RS) by domesticated paddy soil microbes (DPSM) and CH 4 yield of hydrolysate in liquid anaerobic digestion (L-AD). The suitable conditions for HA of RS were carbon/nitrogen ratio (C/N ratio) of 40, 37 oC, inoculum/substrate ratio (I/S ratio) of 2:1, 6.0 cm immersed height, 45% retention rate and 3 HAs, which could obtain maximum volatile fatty acid (VFA) during 5 days of HA due to the relative abundance and characteristic of aerobic (Firmicutes and Actinomycetes) and anaerobic microbes (Bacteroidetes and Acidobacteria). After 3 HAs, the degradation ratio of hemicellulose, cellulose, and lignin in RS achieved 88.45%, 83.19% and 70.09%, respectively.The cumulative methane yield significantly increased from 236.3 to 462.11 mL/g VS as the number of HA increase to 3, and its curve was fitted with the modified Gompertz model very well (R2>0.984)

Keywords: Rice straw, Paddy soil microbes, Hydrolytic acidification, Liquid anaerobic digestion, Methane