Optimization of the Biodegradation of BTEX by Pseudomonas Putida Immobilized In PVA Gel

Ayat El Telib El Tayeb Hassan

Abstract

This thesis examined the biological treatment of gas streams containing Benzene, Toluene, Ethylbenzene and o-Xylene using a spouted bed bioreactor. Organic-degrading bacteria, pseudomonas putida, were immobilized in Polyvinyl Alcohol Matrices. An initial investigation of Toluene degradation was carried out by studying the reduction rate of dissolved oxygen as a function of initial Toluene concentration, residence time, gas flow rate, temperature, Polyvinyl Alcohol volume fraction % and PH.

A parametric study for the continuous biodegrading of Benzene, Toluene, Ethylbenzene and o-Xylene was carried out to evaluate the effect of different operating parameters on the performance of the bioreactor for dual and multi-component mixtures. The effect of Polyvinyl Alcohol Volume fraction in the bioreactor, air flow rate, initial gases concentration, operating temperature, water PH and competitive biodegradation (single, dual and multi-components) on the biodegradation rate were evaluated. In order to determine the best geometry that would provide good mixing and high removal, a larger volume spouted bed bioreactor was built, tested, and optimized for the biodegradation process.

Response surface methodology was used to optimize the biodegradation by Pseudomonas putida immobilized inn Polyvinyl Alcohol matrices in spouted bed bioreactor. The parameters investigated included the contaminated air flow rate, operating temperature, Polyvinyl Alcohol Volume fraction, and water pH. Maximum biodegradation efficiency was predicted to occur at an air flow rate of 500 ml/min, an operating temperature of 33 °C, Polyvinyl Alcohol volume fraction of 30% and pH of 8.3. At optimum conditions, the bioreactor was able to achieve maximum removal efficiency of 94%, 98%, 95% and 98% for Benzene, Toluene, Ethylbenzene, and Xylene, respectively.

A mathematical model was adopted to evaluate the biodegradation kinetics and interaction parameters for dual component at the optimum conditions. Moreover, an effectiveness factor was used to estimate the mass transfer and diffusion limitation for immobilized bacteria compared to free bacteria. The results showed that diffusion resistant may have significant effect on the biodegradation using immobilized Bacteria.