Shinobu�@SAITO

Biogasification of Botanical Biomass (Rice Straw) by Anaerobic Co-digestion with Sewage Sludge

Toshiya KOMATSU, Shuji HIMENO and Shoichi FUJITA

Many existing anaerobic digesters in sewage treatment plants have surplus capacity because they are operated at quite long retention times. Thus, anaerobic co-digestion of sewage sludge and other biomass using existing digesters may be an attractive method for the efficient biogas recovery from biomass. In this study, we focused on botanical biomass (rice straw) as unused resources and investigated the feasibility of anaerobic co-digestion of sewage sludge and rice straw. As rice straw is too solid to feed directly in anaerobic digestion, two pretreatment methods, physical (ground) and thermal pretreatment were examined. After pretreatment of rice straw, mesophilic digesters were operated at various mixture ratios of rice straw to sewage sludge at retention times of 30 days. The results were as follows; rice straw didn�ft have inhibitory effects on digestion of sewage sludge and stable digestion was achieved in all conditions; in order to get methane conversion from rice straw same as sewage sludge, mixture ratio of rice straw to sewage sludge was 1:0.5 in physical pretreatment (5 mm) and 1:1 in thermal pretreatment (120 �Ž, 15 min); COD concentrations increased whereas ammonia nitrogen concentrations decreased in the supernatant of digested sludge by feeding rice straw.