Anaerobic codigestion of sewage sludge and rice straw
نویسندگان
چکیده
We investigated the feasibility of anaerobic codigestion of sewage sludge and rice straw. Laboratory-scale mesophilic and thermophilic digesters were operated with hydraulic retention times of 20 and 15 days, respectively. The feeding ratio of sewage sludge and rice straw was 1:0.5 based on the total solids (TS). Before digestion, the rice straw was ground to ca. 5 mm in length (grinding pretreatment), ground and soaked in distilled water (water pretreatment), or ground and soaked in a hydrolytic enzyme solution (enzyme pretreatment). The effect of these pretreatments on the digestion performance was investigated. A digester fed sewage sludge alone was operated as a control. Both water pretreatment and enzyme pretreatment effectively reduced the TS and volatile solids (VS) of rice straw. The addition of rice straw increased methane production by 66–82% in mesophilic digesters and by 37–63% in thermophilic digesters. Higher methane production was also observed in digesters with water pretreatment and with enzyme pretreatment than in digesters with grinding pretreatment. Specific methane production increased in most cases, and the maximum of 0.311 L/g-added-VS was observed in the enzyme pretreated rice straw mesophilic digester. In addition, a decrease in the ammonia-nitrogen concentration and an improvement in the sludge dewaterability were achieved by the addition of rice straw.
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