Biogas and volatile fatty acid production during anaerobic digestion of straw, cellulose, and hemicellulose with analysis of microbial communities and functions
Authors: Liu Jie , Zuo Xiaoyu , Peng Ke , He Rui 
Published: July 2020

Background
Anaerobic digestion (AD) is a promising method for straw treatment, but the complex composition and structure of straw limit AD efficiency and methane production. The main biodegradable components of straw are cellulose and hemicellulose. Because of the different chemical structures and physicochemical properties, the performance of AD of cellulose and hemicellulose is different, thus it’s also different from that of straw. Research on the similarities and differences of AD of straw, cellulose and hemicellulose is helpful to clarify the law of anaerobic digestion of straw and provide theoretical basis for further improving the efficiency of anaerobic digestion. However, there are very few studies on AD using cellulose and hemicellulose as raw materials.
Results
Rice straw (RS), cellulose, and hemicellulose were used as raw materials to study biogas production performance and changes in the volatile fatty acids (VFAs). Further, microbial communities and genetic functions were analyzed separately for each material. The biogas production potential of RS, cellulose, and hemicellulose was different, with cumulative biogas production of 620.64, 412.50, and 283.75 mL/g·VS− 1, respectively. The methane content of the biogas produced from cellulose and hemicellulose was approximately 10% higher than that produced from RS after the methane content stabilized. Biogas production and the methane content of RS stabilized more quickly than that of cellulose and hemicellulose. The accumulation of VFAs occurred in the early stage of anaerobic digestion in all the three materials, and the main volatile fatty acid component of RS was acetic acid, whereas that of cellulose and hemicellulose was propionic acid. The cumulative amount of VFAs in both cellulose and hemicellulose was relatively higher than that in RS, and the accumulation time was 12 and 14 days longer, respectively. When anaerobic digestion progressed to a stable stage, Clostridium was the dominant bacterial genus in all three AD systems, and the abundance of Ruminofilibacter was higher during anaerobic digestion of RS. Genetically, AD of all the three materials proceeded mainly via aceticlastic methanogenesis, with similar functional components.
Conclusion
The biogas and VFAs production during AD of RS, cellulose, and hemicellulose showed marked differences. But when the AD progressed to the stable stage, there was no significant difference in microbial community and genetic function. Specifically, the biogas production potential of cellulose and hemicellulose was greater than that of RS. The accumulation of VFAs in the three AD systems occurred in the early stages. The main component of VFA that accumulated in RS was acetic acid, while the major component of VFAs accumulated in cellulose and hemicellulose digestions was propionic acid. At the stable stage, Clostridium was the dominant bacterial genus in all three AD systems. The AD of all the three materials proceeded mainly via aceticlastic methanogenesis, with similar components of gene functions.