Thermophilic anaerobic co-digestion of rice straw and organic wastes

• Main Authors: Wei-Ting Chou, 卓威廷
• Other Authors: Wen-Chien Kuo
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/58304128933234123883

碩士 === 國立屏東科技大學 === 環境工程與科學系所 === 97 === This study investigated the co-digestion of high fiber content straw, with easily digested kitchen waste, and sludge from swine wastewater. This composite substrate was fed to a laboratory-scale two-phase reactor semi-continuously under thermophilic anaerobic conditions. The results can provide for subsequent scale up and full scale applications. The straw was characterized to provide 1.236 g COD/g. In the kitchen waste, the average TCOD was 158.3 g/L, indicating a high organic content waste. The TCOD/TKN and TCOD/TP were 326.9 and 474.9 respectively, indicating a possible deficiency of N and P. In the swine wastewater sludge, the TCOD/TKN and TCOD/TP were 110.7 and 107.0 respectively, indicating when co-digestion with kitchen waste the swine wastewater sludge could provide for more N and P. In physical-chemical pretreatment of the straw, three concentrations of sulfuric acid (0.5N, 1.0N, and 2.0 N) were added to treat for 12 hours under the temperature of 90oC, and the hydrolysis ratios were found to be 44.8%, 43.3%, and 44.1%, respectively. It was found that this kind of pretreatment needs to provide energy for heating and inorganic acid which would increase the cost of the processes. In the biological pretreatment of the straw, when mixed with acetogens for 48 hours at different temperatures, it was found that at 55oC had the highest hydrolysis ratio of 37.14%. This performance was better when the straw was mixed with kitchen at 55oC for 48 hours, which had the hydrolysis ratio of 27.20%. The reducing sugar concentration could reach as high as 648 mg/L when straw was treated with acetogens at 55oC for 240 hours. When bubble respirometer was used to evaluate the co-digestion of straw, kitchen waste, and swine wastewater sludge, a ratio of 5:4:1 was found to have the maximum gas production of 328.6 mL. Among all other ratios, the COD removal efficiencies were only 17.6-31.3%, indicating the difficulties of digestion when straw contributed the significant portion of the feed. Organic wastes were co-digested using Semi-Continuously Stirred Tank Reactor (S-CSTR) under thermophilic conditions (55oC). When the system was operated at the Organic Loading Rate (OLR) of 2 g COD/L-d and the Hydraulic Retention Time (HRT) of 20 days with the feed ratio of 5:4:1 (straw : kitchen waste : swine wastewater sludge), the average gas production was 3.1± 1.8 L/d. At the later stage of the test (47th day to 67th day) when gas production was stabilized, the biogas recovery could reach 61.8-72.3%. Mean methane and carbon dioxide concentrations in the biogas were 62.5± 3.1% and 31.0± 1.9%, respectively, indicating that the system was behaving normally. The TCOD removal efficiency could reach 61.0% at 67th day.