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Demand-oriented conversion of biogas is conducive to meeting the needs of biogas supply and reduces extra costs related to gas storage facilities. In this study, the effect of feeding regimes (FRs) on anaerobic digestion performance and microbial community structure of rice straw were investigated using continuously stirred tank reactors. The result showed that compared to the FRs of every day and every 6 days, the FR of every 3 days achieved the best biomethane yield and substrate conversion rate, which improved by 17.3% and 12.4%, respectively. Additionally, the FR of every 3 days had a significant impact on microbial richness and diversity, and also improved the abundance of dominant archaea Methanosaeta. This indicated that the FR of every 3 days was suitable for the growth rate of Methanosaeta, which resulted in better anaerobic digestion performance. A narrow FR is helpful to meet the demand-oriented conversion of biogas.

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Combined pretreatment using CaO and the liquid fraction of digestate (LFD) was proposed as an eco-friendly pretreatment method for high-quality anaerobic digestion (AD). In this study, rice straw was pretreated by CaO–LFD at three pretreatment temperatures (5, 20, and 35 °C) and four pretreatment times (1, 2, 3, and 4 days). The results showed that the optimum pretreatment condition for rice straw was 35 °C for 2 days. In this case, the maximum biomethane yield reached 308 mL g–1 of VS, 77.4% higher than that of the control. The Fitzhugh and Cone models were demonstrated to be more suitable for CaO–LFD pretreated rice straw in the AD process. AD of pretreated rice straw had a shorter effective biomethane production period and lag phase time, exhibiting high AD efficiency. This study enhances the knowledge about CaO–LFD pretreatment from multiple angles, in addition to demonstrating promising possibilities for practical application.

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