Abstract
Anaerobic co-digestion of sewage sludge and currently unused biomass has been paid attention. In this study, we focused on the utilization of rice straw. We conducted continuous experiments using pilotscale digesters at a sewage treatment plant for establishment of practical application of the co-digestion technology.
Rice straw was ground to about 2-3 mm in length, and then pretreated by soaking with water or enzyme-water. Two digesters were fed sewage sludge with (1) water soaked rice straw, (2) enzymewater soaked rice straw. A digester fed sewage sludge alone was operated as a control.
The digesters were operated under the condition that the mixture ratio of sewage sludge and rice straw were 1:0.5 and 1:0.75 based on TS. When the mixture ratio was 1:0.5, the operation was satisfactory and the specific biogas production (SBP) of rice straw was as high as 342-377 NL/kg-VS. The SBP dropped to 218-242 NL/kg-VS in the mixture ratio of 1:0.75. In both cases, higher SBP was obtained by using enzyme pretreatment.
