Factor affecting the degradation of waste activated sludge by thermophilic bacteria

• Main Authors: Jing-Yung Weng, 翁靖媛
• Other Authors: 李季眉
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/24453545213816197224

碩士 === 國立中興大學 === 環境工程學系所 === 95 === As a considerably new and dynamic technique, Thermophilic Aerobic Digestion (TAD) is highly acclaimed for its efficient sludge reduction and pathogen destruction. To determine the best operating strategies for sludge decomposition under the TAD reactor, a series of batch experiments were carried out to uncover factors affecting the degradation of waste activated sludge. This study was composed of five main parts. The first part was a preliminary study on the characteristics of Geobacillus caldoxylosilyticus N6. Based on the experimental results, the optimum temperature for the growth of Geobacillus caldoxylosilyticus N6 was 65℃, and the range of optimum pH values was 6.9~8.5. If the concentration of MnSO4 in the medium was 300 mg/L, Geobacillus caldoxylosilyticus N6 could produce endospore after inoculating 1 day. And when concentration of MnSO4 was between 25 mg/L~600 mg/L, equally substantial amount of spore would be formed in three days after inoculation. Moreover, the addition of various metal ions and nitrogen sources also influenced the growth of Geobacillus caldoxylosilyticus N6, so does these various concentration of additives on N6. The second part was an investigation into the optimum operating condition for Thermophilic Aerobic Digestion. The results indicated a best MLVSS removal efficiency, which was 41%, was achieved at 65℃, MLSS concentration of 14000 mg/L, and without pH control when the sludge was heated (80℃, 1 hr) and shattered (10 min) as pretreatment. Thus, in the future experiments, this could be a perspective approach for improving the efficiency of sludge decomposition. The third part was an attempt to find factors leading to declining removal efficiency in a later period. The experiment results illustrated that the main reason lay in the inactivity of thermophilic bacteria in a later stage, accompanied by an accumulation of inhibitors in the sludge digestion tank, which hampered efficient sludge decomposition. Then, the forth part looked into how to improve digestive efficiency. The results suggested that different concentration of additive metal ions made a difference. As the best removal efficiency of MLVSS at 50% was generated with 2 mM Ca2+ added, the addition of Zn2+ only slowed down the process, and the higher concentration of Zn2+, the lower efficiency was achieved. Also, while low Fe2+ concentration enhanced sludge biodegradability, high Fe2+ concentration only turned out a counteraction. As for adding different nitrogen sources, there was no significant influence on sludge decomposition. Efforts were made on the final part to discern the optimal operating condition for sludge biodegradation, as well to probe into sludge from other places. Indicated by this study, the optimal operating condition also pertained to wasted activated sludge of a wastewater treatment plant in Taichung.