High-Efficiency Mesophilic Biogasification Of Rice Straw By Anarobic Digestion

Anaerobic digestion is one of the feasible technologies to utilize the rice straw, which can convert it into biogas. But little research has been conducted on the anaerobic digestion of rice straw to biogas. The main reason is that raw rice straw contains high percentage of lignocellulose, which is not readily biodegradable by the anaerobic bacteria, leading to lower digestion rate and biogas production. Pretreatment has been proved to be an effective way to improve the biodegradation efficiency and biogas production.This study investigated the biodegradability of untreated rice straw, retted rice straw and 6% NaOH-treated rice straw at different loading rates (35g/L, 50g/L, 65g/L, 80g/L) under mesophilic conditions, which could provide useful parameters for the design of large-scale anaerobic digestion of rice straw for biogas production.The results showed that the biodegradability of untreated rice straw was inhibited by high loading rates 65g/L and 80g/L. It achieved the highest biogas yield at the 50g/L loading rate, which was 0.31L/gTS. The total biogas production, methane content of biogas and technical digestion time for untreated rice straw were 23.05L 50.65% and 32days respectively.The retting pretreatment could improve the biodegradability of the rice straw significantly. The total biogas production was increased by 4.05%-52.2%. Among the nine kinds of retted rice straws, the 1# retted rice straw achieved the highest biogas yield at the 50g/L loading rate, 0.41L/gTS, which is 32.26% higher than the biogas yield of untreated rice straw. The total biogas production, methane content of biogas and technical digestion time for 1# retted rice straw were 30.56L, 52.51% and 32 days respectively.The NaOH chemical pretreatment also improved the biogas production and biogas production rate of untreated rice straw significantly. The total biogas production was 13.79%-48.14% higher than that of untreated rice straw. It also achieved the highest biogas yield at the 50g/L loading rate, which was 0.41L/gTS. In addition, the effect of particle size on the anaerobic digestion rate of the NaOH-treated rice straw is indistinctive. The biogas yields of them were all around 0.29L/gTS.Therefore, the digestibility of the two kinds of rice straw pretreated by retting (1#) and 6%NaOH are comparable. Either of them can be applied to pretreat the rice straw, and 50g/L is recommended to be the optimum loading rate for both of the two kinds of rice straw.