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Bioremediation of Soils Contaminated by Polychlorinated Biphenyls

Dehghani Mohammadabadi, Fatemeh | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52572 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Yaghmaei, Soheila; Ghobadi Nejad, Zahra
  7. Abstract:
  8. Polychlorinated Biphenyls are a class of organic compounds that are composed of two biphenyl rings attached by 1-10 chlorine atoms. Due to their specific properties, such as physical and chemical stability, flame resistance, and dielectric properties, these compounds are used as dielectric liquids, heat-exchange fluids, hydraulic liquids, plastifiers, and especially as Askarel oil in power plant transformer. Because of their high persistency in the environment, high toxicity, and bioaccumulation in the adipose tissue of humans and animals, their production is banned in most countries, and their use has been limited. There are different methods for detoxification of these compounds, and in comparison with other conventional methods, bioremediation is an environmentally friendly and economical approach. Considering previous research and the possibility of bioremediation of polychlorinated biphenyls in water, using two bacterial strains Lysinibacillus macrolides DSM54T and Bacillus firmus NBRC15306T that were previously isolated from PCB-contaminated soil, biodegradation of 4-chlorobenzoic acid was done in soil microcosms, and biodegradation percentage was calculated by UV-Visible Spectrophotometer. In addition, it was found that the growth of these microorganisms in soil and chloride release correlated with the biodegradation of 4-CBA. Also, using Design-Expert software and Response Surface Methodology, by choosing four parameters, that is, temperature (20-60 °C), initial pollutant concentration (50-250 mg/kg dry soil), moisture (20-40 % v/w), and inoculum size (4-20 % v/w), 30 experiments were designed by the software. The experiments were done in the specific conditions of parameters, and biodegradation percentage was achieved by experimental results. Finally, in order to determine maximum biodegradation percentage, optimization was done by the software. The suggested optimized response by the software was 91 % biodegradation in 24.8°C, 150.5 mg 4-CBA/ kg dry soil, 33.8 % moisture, and 10 % inoculum size as well as 92.2 % biodegradation in 46.9°C, 172.1 mg 4-CBA/ kg dry soil, 21 % moisture, and 6.9 % inoculum size
  9. Keywords:
  10. Optimization ; Bioremediation ; Response Surface Methodology ; Polychlorinated Biphenyls ; Bacillus Firmus ; 4-Chlorobenzoic Acid ; Lysinibacillus Macrolides

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