Producing Biogas from Rice Straw: Kinetic Analysis and Microbial Community Dynamics

Biogas production by anaerobic digestion is an attractive approach to producing clean fuel biomethane and reducing environmental pollution. However, many fluctuations in production occur during a batch digestion period. This study investigated the dynamics of microbial communities involved in biogas production during a 20-day digestion of rice straw (RS) at 35 °C. The results demonstrated roughly consistent trends in biogas and methane production and revealed distinct stages of production. The lowest and peak methane yields were 82 ± 19.9 mL/(L•day) at day 3 and 328.5 ± 0.9 mL/(L•day) at day 8, respectively, whereas most (97.1%) of the methane was produced in the first 14 days of digestion. Ultimately, the biogas potential of RS reached 393.2 ± 13.6 mL/g added volatile solids (CH4% = 57.1%), and the logistic model best fitted actual methane production compared to the modified Gompertz, first-order kinetic, and Cone models. The microbial communities at different critical stages are a clear reflection of the biochemical dynamics in digesters. The bacterial genera Bacteroides and Clostridium_sensu_stricto_1 were the dominant microorganisms at the early stage of digestion, while the archaeal genus Methanosarcina was significantly more abundant at the peak stage of methane production than at other times during the digestion. This study demonstrates the detailed micro- and macro-conditions that exist during the fluctuating and constant digestion of RS, which will benefit industrial applications during the anaerobic digestion of RS.