Biotreatment of waste streams containing isopropyl alcohol and copper from semiconductor manufacturing

摘要

Because of the nature of their processes, semiconductor fabrication facilities use a large amount of water for the processing of microchips. This also means that a large amount of wastewater is discharged from semiconductor facilities. Because of this, there is a drive in the industry towards decreasing water consumption and wastewater discharge by optimizing processes and minimizing water usage, as well as by recycling and reusing wastewaters. The majority of aqueous wastewaters in semiconductor manufacturing come from rinse processes used after chemical baths during cleaning and also from chemical and mechanical planarization processes. This work focuses on the use of biological treatment as a chemical and energy efficient alternative for treating waste streams containing isopropyl alcohol (IPA) and copper. A consortium of bacteria capable of degrading IPA was selected and acclimated. This consortium was immobilized on activated carbon and used as packing for a fluidized-bed reactor. The bioreactor was able to degrade more than 95% of the IPA in the feed stream. In addition, the behavior of the bioreactor system was studied under transient feed conditions by introducing a series of pH and IPA shocks after the reactor had reached steady state. A 5X (500 ppm) step change of IPA in the feed caused the effluent IPA concentration in the reactor to increase ∼12%. After the step change was finished, the reactor quickly recovered to its steady state level. Similarly, a step change decrease in pH of the feed from 7 to 4 caused an ∼11% increase in effluent IPA concentration. A mathematical model based on diffusion and biodegradation of IPA through the biofilm as well as adsorption of IPA on the activated carbon was developed and tested. The model was able to predict the transient changes in IPA feed concentration very well. Finally, building upon the results of previous research studying the biosorption of copper on immobilized cells, a system for the simultaneous removal of IPA and copper was tested experimentally. After acclimation, the system was able to treat effectively a model wastewater containing 100 ppm of IPA and 50 ppm of copper.