Pilot-scale Experiment for Practical Application of AnaerobicCo-digestion Technology of Sewage Sludge and Rice Straw

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Anaerobic co-digestion of sewage sludge and currently unused biomass has been paid attention. In this study, we operated pilot-scale digesters for practical application of the co-digestion technology of sewage sludge and rice straw. Before the pilot-scale study, laboratory-scale anaerobic digestion experiments were conducted in order to determine the pretreatment conditions of rice straw in the pilot-scale experiments. 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 25 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 and enzyme pretreated rice straw were 48% and 72% (COD basis), respectively. This study demonstrated that rice straw is a feasible biomassapplicable to co-digestion technology in sewage treatment plants.