Effects of Anaerobic Co-digestion of Sewage Sludge and Rice Straw for Energy Balance and Greenhouse Gas Emission

Abstract

This study focuses on the evaluation of energy balance and greenhouse gas (GHG) balance on mesophilic anaerobic co-digestion of sewage sludge and rice straw between co-generation of electricity system and production of methane gas system. The boundary for this evaluation was assumed from rice collection to final disposal of sewage sludge. As the result of evaluation, 132Nm³ of methane gas was obtained from 1Mg of rice straw. It was also found that the smallest energy consumption and the largest reduction of GHG emission were given by co-generation of electricity system including the co-digestion with sewage sludge and rice straw. Although the waste heat from the co-digestion could contribute to heat solubilizing and digesting reactor, it could not be used for drying dewatering sludge cake. Besides, the production of solid fuel from sewage sludge cake was essential for the anaerobic co-digestion system because it improved the energy and GHG balance.