Novel Insights into Anaerobic Digestion of Rice Straw Using Combined Pretreatment with CaO and the Liquid Fraction of Digestate: Anaerobic Digestion Performance and Kinetic Analysis

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–1of 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.