Kyohei KUDO

Effect of Pretreatments for Enhancing Anaerobic Digestibility of Rice Straw

Toshiya KOMATSU , Shoichi FUJITA , Shuji HIMENO


Rice straw is produced in large quantities (about 650 thousand ton each year) as a by-product of rice production in Niigata Prefecture, but the effective utilization of rice straw has not been established. Anaerobic co-digestion of sewage sludge and other biomass using existing digesters has a possibility for effective utilization of biomass. In this study, we focused on rice straw as unused biomass and investigated the feasibility of anaerobic co-digestion of sewage sludge and rice straw.

Since the structure of rice straw is firm, some pretreatment is necessary in order to enhance anaerobic digestibility of rice straw. We examined the effect of using a hydrolytic enzyme in pretreatment of rice straw. First, batch anaerobic digestion tests were conducted using enzyme pretreated rice straw to determine effective conditions of enzyme pretreatment. Then, continuous digesters were operated at mixing rice straw to sewage sludge TS ratios of 1:0, 1:0.5 and 1:1 with retention times of 30 and 20 days. As the results, enzyme pretreated rice straw showed better performance in both solid reduction and methane conversion, compared with grinding pretreatment alone or water pretreatment. Methane conversion efficiency of enzyme pretreated rice straw reached more than 90% on COD basis at mixing ratio of 1:0.5. In addition, the decrease of ammonia nitrogen and the improvement of sludge dewaterability were observed by mixing rice straw.