Effect of mixing rates on anaerobic digestion performance of rice straw

In order to improve the efficiency of anaerobic digestion of rice straw, the effect of mixing rates on anaerobic digestion performance of rice straw was investigated in batch mode at the mesophilic temperature of 35℃. Three mixing rates of 120, 80 and 40 r/min were used. The results showed that anaerobic digestion performance was influenced significantly by mixing rates. The mixing rate of 120 r/min achieved biogas yield of 451.6 mL/g, which was 20%, and 107% higher than those of the mixing rates of 80 and 40 r/min respectively. The former technical digestion time T80 (the time to reach 80% of the total production) was 46 days, which was 16 days shorter than that of the mixing rates of 80 r/min, implying the higher digestion efficiency. The proper pH and alkalinity at higher mixing rate enhanced the mass transfer and contributed to the higher biogas yield, more degradation of mass (TS and VS) and the stability of anaerobic system.