Enhanced hydrolysis of excessive activated sludge by microwave

• Main Author: Chee, Kian Hao.
• Other Authors: Liu Yu
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/15927
• Institution: Nanyang Technological University

Sludge production has been steadily increased over the years. In U.S. alone, approximately 6.3 million metric tons of municipal wastewater sludge was produced in 1998. This is projected to increase to 6.9 million and 7.4 million metric dry tons in the years 2005 and 2010 respectively. Anaerobic digestion is responsible for sludge stabilization as well as the production of biogas in the form of methane. However, hydrolysis of waste activated sludge (WAS) is seen as the rate limiting step during sludge digestion. In this study, microwave treatment will be investigated as a possible technique for sludge disintegration. Microwave has the ability to excite dipolar molecules. Water, which is a dipolar molecule, is the main component of sludge. Theory wise the water molecules in the sludge should be readily excited when exposed to microwave. This should cause cellular disruption and speed up the hydrolytic process. The purpose of this study is to enhance the efficiency of anaerobic digestion of WAS by microwave treatment. The outcome of this study shall determine if microwave pretreatment is suitable to be used before anaerobic digestion. Changes in cellular viability, morphology and settleability of WAS after microwave treatment are discussed. The study also looks into the possibility of using microwave treatment together with addition of chemicals as a combined technique for pretreatment of WAS. Results showed that the disintegration efficiency seems to be improved by increasing microwave power, exposure time and sludge concentration. The best disintegration efficiency was observed at 3g TSS/L sludge sample after 60s of microwave treatment at 800W. Changes in bacteria cells morphology was also observed after microwave treatment at 600W for 60s. The cells seem to have shrunk, lacked cellular fluid and appeared clumpy. The SVI tests showed that sludge settleability seems to be improved only at a certain microwave power and exposure time. More studies are required to find out the suitable microwave power and exposure time to increase sludge settleability. Microwave treatment with the addition of alkaline seems to improve the disintegration remarkably. Whereas microwave treatment with the addition of acid did not improve disintegration as much as microwave treatment alone did. Generally, microwave treatment can improve disintegration efficiency of WAS. However, more studies are still needed to optimize the use of microwave as a pretreatment technique. Combined technique using microwave with the addition of alkaline also showed promise of increasing disintegration efficiency.