Abstract
The blooming of semiconductor industry has brought serious concerns over its negative environmental impacts. The exhausts from the semiconductor industry contain volatile organic compounds, eq acetone。As acetone waste gases exist in atmosphere, it could cause the health and environmental problems. In the light of increasingly stringent regulations of air emissions of volatile organic compounds (VOCs), technologies that control VOC emissions have received much attention in recent years. Bioprocess is a preferable alternative to other conventional physical and chemical methods for purification of the waste gases contain with large volume and low pollution concentration VOC. The reasons lie mainly in low operating cost, good operational stability, and high destruction efficiency of pollutants. This study investigates the environmental factors affecting biodegradation of acetone and then use polyacrylamide (PAA) as support matrix for entrapment of cells, investigate the degradation of acetone using immobilized-cell beads, and examine the environmental factors affecting biodegradation of acetone. Finally, the results will be compared with that using suspension cells.The effect of pH and temperature on acetone degradation by free and immobilized Thiosphaera pantotropha, the data show the immobilized system showed a wider operating range of optimal pH and temperature. The acetone degradation efficiency was 100％for initial acetone concentration less than 400 mg / L, but it decreased with further increase in acetone concentration。When the acetone concentration was as high as 700 mg / L, almost 60％ of the acetone was removed by free Thiosphaera pantotropha. However, when the acetone concentration was as high as 700 mg / L, almost 100％ of the acetone was removed by immobilized with Thiosphaera pantotropha.In order to enhance economical efficiency, optimal cheaper supplementary nitrogen sources were also used to determine the acetone degradation efficiency. The sodium nitrate would be the most effective supplement to used as a nitrogen source to support acetone degradation process。For the free cells, the maximum reaction rate and Michaelis-Menten constants were determined as Vm= 7.4 mg acetone / g dry cell / hr, Km=100 mg acetone / L, respectively. For immobilized cells in 2.56~4.26 mm diameter particles, Vm= 6.57 mg acetone / g dry cell / hr, Km=123、151 and 203 mg acetone / L, respectively. Repeated batch experiments shows the relative acetone degradation capacities increased with repeated times increased。After six times of batch experiments, the relative acetone degradation capacity of PAA was still above 100％ and showed the beads had the elasticity and high mechanical strength。