Biodegradation Of MTBE By Chryseobacterium Sp. A-3

Methyl tert-butyl ether (MTBE), is one of the most commonly oxygenates presently used as a gasoline additive since 1978, which can boost the octane index of unleaded gasoline and improve the quality of air by reduction of polluting emissions in exhaust gases. However, with its widespreadly used, it has beome one of the frequently detected pollutions in soil and groundwater by its release from leaking underground strorage tanks or other accidents caused by improperly using. Now, the use of MTBE as a gasoline additive has been a controversial subject, and many countries including the U.S.A has put up a ban for its use, and that how to remediate the soil and groundwater polluted by MTBE has become a hot topic in research abroad for MTBE can stay in the environment by its uneasy degradation. While, at home, the monitoring and the treatment of MTBE have not been put on enough emphasis, and there has been few papers related reported up to now.In this study, a bioremediation technique was considered for MTBE pollution treatment by isolating a bacterium named A-3 to biodegrade MTBE most effectively from the microorganisms after two-month acclimatization, and the microorganisms were oringally got from MTBE-polluted soil. Then strain A-3 was identified as a genus of Chryseobacterium sp., and it was found the strain can degrade the most of MTBE with a removal ratio of 56% and a rate between 0.039 and 0.0875 g MTBE/ (gd w.d) under experimental conditions optimized in the following that seeding amount was about 2.0×10 8 c ells/ml, pH was 6.5-7.5, temperature was 28-30℃, liquid volume was 50 ml, and the concentration of MTBE was 50-100 mg/L.In addition, the biodegrading characterization of Chryseobacterium sp. A-3 to remove MTBE was studied. As previously studies, the process of strain A-3 to degrade MTBE required high level of dissolved oxygen with an apparent half-saturation constant of 8.76 mg/L. The overall biomass yield was estimated for 0.33 gdw/gMTBE,and the mineralization to CO2 was 38.1%.The results of GC/MS analysis showed that the main metabolic intermediates were tert butyl achohol(TBA),2-hydroxy isobutyrate(HIBA) and acetone, which indicated that strain A-3 degraded TBA by the acetone pathway reported by others. Besides, the degrading curve of MTBE by strain A-3 was well fit with the Gompertz model. Interestingly, it was also found BTEX(benzene,toluene,ethylbenzene and p-xylene) can increased the degrading ratio of MTBE by 20% during the degrading course in this study, which benefited a lot to the bioremediation of MTBE in practice.Finally,the key enzymes involved in biodegradtion of MTBE were tentatively studied, and the results showed that the enzymes were induced type located in intracellular, and furtherly proved to be monooxgenases excluding cytochrome P-450 enzymes. And the mechanism of the interaction between MTBE and the monooxygeases need to be furtherly researched.