The digesters were placed in a constant-temperature trough (water-heated, 1°C fluctuation) using a temperature controller that relayed the display. The biogas generated in the digester was transported into the headspace of the bottle using a glass pipe. The water in the bottle was then pressed out and overflowed into the receiver through another glass pipe. The volume of the discharged water from the bottle represented the volume of the biogas generated in the digester.
Each pretreated rice straw was used as the digestion material, with the untreated rice straw as the control. Each treatment was performed in triplicate. The volume of each digester was 1 L, with 0.75 L working volume, and the fermentation process lasted for 30 days. The digesting material (500 g) and inocula (200 g) were added to each digester, and deionized water was added as necessary to obtain 8% TS content (Song et al. 2010). Moreover, the anaerobic fermentation was set at 37°C to eliminate the effect of the inocula, and 200 g of the inocula were digested and served as the blank. At the end of the experiment, the pretreated rice straw was dried in an electronic oven (HengFeng SFG- 02.600, Huangshi, China) at 80°C for 48 h and then kept in a refrigerator for composition determination and AD experiments to investigate the effect of different chemical treatments on biogas production.