Ryou TAKAMATSU
Anaerobic Co-digestion of Sewage Sludge and Rice Straw for Practical Application of the Biogasification Technology
Toshiya Komatsu, Syuji Himeno
Anaerobic co-digestion of sewage sludge and currently unused biomass has been paid attention. Our previous laboratory-scale study suggested that rice straw, which is producedin large quantities as anagricultural by-product, is a possible biomass for co-digestion with sewage sludge. The use of a hydrolytic enzyme was effective for enhancing anaerobic digestibility of rice straw.
In this study, we operated pilot-scale digesters for the practical application of the co-digestiontechnology of sewage sludge and rice straw. Before the pilot-scale study, laboratory-scale anaerobic digestion experiments were conducted using rice straw ground by a pilot-scale crushing machine, and the effective pretreatment conditions were determined.
Pilot-scale equipment was installed in a sewage treatment plant.Three digesters having 500 L working volume were operated. Two digesters were fed sewage sludge with (1) water solubilized rice straw, (2) enzyme-water solubilized rice straw. The feeding ratio of sewage sludge and rice straw was 1:0.2 based on TS. A digester fed sewage sludge alone was operated as a control. The digesters were operated for 9 weeks with hydraulic retention times of about 30 days.
As the results, higher TS removal and biogas production were observed by mixing rice straw. In the apparent steady-state condition, methane conversion efficiency of water pretreated rice straw andenzyme pretreated rice straw were 48% and 72% (COD basis),respectively. This study demonstrated that rice straw is a feasible biomass applicable to co-digestiontechnology in sewage treatment plants.
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