Biodegradation of trichloroethylene using plant terpenes as inducer

Abstract

Trichloroethylene (TCE) has been used extensively as a solvent and degreasing agent. Due to its widespread contamination and potential health threat, remediation technology to clean-up TCE is necessary. TCE co-metabolism by aerobic bacteria is well established using phenol, toluene or methane as growth substrate and enzyme inducer. However, these compounds should not be applied to a TCE contaminated site because they are regulated as hazardous materials. The objectives of this study were to identify an alternative enzyme inducer as well as to apply the induced bacteria for degradation of TCE in contaminated soil. Terpenes, the main components in volatile essential oils of plant associated with plant characteristic fragrances were investigated for their ability to induce TCE degradation in Rhodococcus gordoniae P3 (Gram positive) and Pseudomonas sp. T1 (Gram negative), the isolated bacteria found in Bangkok soil. Selected terpenes, including cumene, limonene, carvone and pinene at various concentrations, were used in this study. The most effective terpene for enzyme induction was cumene, in which Rhodococcus gordoniae P3 induced with 25 mg l [superscript -1] cumene and Pseudomonas sp.T1 induced with 10 mg l [superscript -1] cumene degraded 76% and 61% of 10 ppm TCE in 24 hours, respectively. Moreover, the bacteria were able to completely degrade TCE (mineralization), which was indicated by a correlation between TCE reduction and chloride ion accumulation in the bacterial culture. Since, Rhodococcus gordoniae P3 degraded TCE more efficiently, it was selected for of the biodegradation of TCE contaminated soil. Soil microcosms were later conducted to investigate the ability of cumene and cumene induced cells for TCE bioremediation. There were two bioremediation treatments; bioaugmentation, the inoculation of 25 mg l [superscript -1] cumene-induced Rhodococcus gordoniae P3, and biostimulation, the addition of 25, 50, and 100 ppm cumene to induce the indigenous soil microorganisms to degrade TCE. Bioaugmentation and biostimulation were shown to significantly accelerate TCE reduction when compared to control treatment, especially at the beginning of the test period. Approximately 60% and 70% of 100 ppm TCE was reduced during the first 4 days of incubation in biostimulation and bioaugmentation treatment, respectively.