Bioremediation of petroleum hydrocarbon contaminants by bioreactor
Methyl tert-butyl ether (MTBE) has been the most commonly used high octane additive to gasoline since 1990. The compound is partially water soluble and moderately volatile; thus, it is highly mobile in both groundwater and surface water and can be volatilized to contaminate the vadose zone, surface soils, and sediments. However, biological treatment of MTBE-contaminated groundwater appears to be the most economical, energy efficient, and environmentally sound approach. The objective of this reach was to investigate the biodegradation potential of MTBE by the microorganisms specified (Pseudomonas sp., Bacillus sp., Klebsiella sp., Enterobacter sp.) at a petroleum contaminated site. It was intended to evaluate the pure culture with the best ability of biodegradability of MTBE and to evaluate the biodegradation pathway for these microorganisms. MTBE can be metabolized by bacteria either as a primary carbon source, or cometabolized when bacterial growth requires another substrates at the batch experiments involving either mixed or pure cultures. The bioreactor with conditions obtained from the batch experiment was applied to enhance degradation of MTBE. The metabolic pathways and cellular responses of these microorganisms during growth on MTBE were studied through proteomics approach. Protein spots of interest were identified through database searching according to peptide mass fingerprints (PMFs) obtained using matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). The pentane was used as the cometabolic chemical to enhance MTBE degradation. On the other hand, the pure culture (Enterobacter sp. NKNU02) shown the best degradation potential about 29 % of MTBE without adding pentane. Enterobacter sp. NKNU02 could degrade about 56 % of MTBE without adding pentane. Bacillus sp. NKNU01 and Klebsiella sp. NKNU01 could degrade about 22 % of MTBE with adding pentane. Comparing with the batch experiments, bioreactor could enhance MTBE degradation significantly. Four metabolic enzymes may involve alcohol dehydrogenase, phosphor- glyceromutase, transaldolase, and isocitrate dehydrogenase. Assessing the potential products of MTBE degradation by gas chromatograph/mass spectrometer(GC/MS) involved acetic acid, 2-propenoic acid, and 2-propanol. Enterobacter sp. NKNU02 followed the pathway in the initial steps of MTBE degradation, without converting MTBE to tert-butyl formate, which was directly hydrolysed to tert-butyl alcohol, and then transformed 2-propanol and lactate to the TCA cycle (tricarboxylic acid cycle). MTBE and BTEX (benzene, toluene, ethylbenzene, and xylenes) can coexist in gasoline-contaminated groundwater, and MTBE-degradability of Enterobacter sp. NKNU02 could reduce about 16% of MTBE but inhibited by BTEX. However, it could also degrade BTEX including 36% of toluene and 32% of benzene. The effectiveness of bioremediation of MTBE will be assessed for potential field-scale application.
Methyl tert-butyl ether, biodegradation, bioreactor, cometabolism, pentane