Biodegradation Mechanism Of MTBE And Transport Process Of Bacteria In Underground Surroundings

Methyl tert-butyl ether (MTBE) is widely used in gasoline additive and causes severe environmental pollutions. Recently, it attracts more attention due to its toxic and recalcitrant properties in the environment. Compared with conventional methods, biodegradation is more economical and effective for the remediation of MTBE pollution. In this study, a bacterial culture possessing effective degradation ability was isolated. Based on which, the systematical studies on the degradation characteristics, mechanism and bacterial transport in the bioremediation process were carried out.A bacterial culture named A-3 which could effectively degrade MTBE was isolated from the MTBE contaminated soil. It was identified as Chryseobacterium sp., a new species capable of degrading MTBE. The effects of environmental factors such as temperature, pH values, inoculating sizes and MTBE concentrations on MTBE degradation were optimized. The ability of this isolate growing in glucose and MTBE as carbon source was compared and the slow growth in MTBE was explained. The mineralization experiments of MTBE biodegradation were also conducted to estimate the ability of the isolate.To better understand of the mechanism involved in MTBE biodegradation, the main metabolic intermediates were determined by SPE-GC/MS analytical method. Furthermore, the effect of tert-butyl alcohol (TBA) on MTBE degradation was also investigated, and the difference of the key enzymes involved in biodegradation between MTBE and TBA was examined. SDS-PAGE analysis of the crude extracts obtained from the cells growing in MTBE and TBA cultures demonstrated that there presence seven similar peptides in both extracts. The experiments in plasmid purification and elimination further suggested that the degrading function might be controlled by chromosome DNA other than plasmid.In order to improve the degradation ability of Chryseobacterium sp.,β-cyclodextrin was used to enhance the MTBE degradation rate. The effects of cometabolic substrates on the degradation of MTBE were also explored and the results indicated that glycerol was the best cometabolic substrate to promote the degradation rate and shorten the period. All the mentioned researches give new approached for MTBE removing. To predict the behavior of MTBE, the adaptability of the isolate and the effects of BTEX on the degradation of MTBE were examined.In order to apply Chryseobacterium sp. into the bioremediation in MTBE contaminated site, the transport of bacteria in porous media and the influence factors were investigated. A mathematical model describing the adsorption with two fractions was proposed. Based on the model analysis and simulation, the effects of infiltration rate and bacteria concentration on transport were discussed. Moreover,a completely coupled model for microbial and substrate transport in soil were developed combining bacterial adsorption, desorption, growth and decay. The transport performances of Chryseobacterium sp. and substrate in the bioremediation processes were described.