Effects of rice straw ratio on mesophilic and thermophilic anaerobic co-digestion of swine manure and rice straw mixture

Abstract

The mesophilic and thermophilic anaerobic co-digestion (Co-AD) of swine manure (SM) and rice straw (RS) mixtures was evaluated in lab-scale continuously stirred tank reactors through long-term semi-continuous experiments to investigate the effects of three RS ratios (25%, 33.3%, and 50%, based on total solids). The experimental results showed that an increase in the RS ratio reduced the biogas and methane production, and methane content in both Co-ADs and the effects of the increased RS ratio on the mesophilic Co-AD (Co-MAD) were slightly lower than those on the thermophilic Co-AD (Co-TAD). The digestate characteristics were also affected by the RS ratio. A reduction analysis demonstrated the higher importance of the RS ratio in the substrate with respect to gas production in Co-MAD compared to Co-TAD. The increase in the RS ratio increased the relative abundance of Clostridium_sensu_strricto_1, and changed the predominant archaea and methanogenesis pathways in both Co-ADs.