Saturday, 15 July 2006

Bioremediation of PAHs Contamination Soil by Biosurfactants Producing Bacteria A. calcoaceticus BU03 under Thermophilic Composting Systems.

Jonathan WC Wong, Dept of Biology, Hong Kong Baptist Univ, Kowloon Tong, Hong Kong, China

Polycyclic Aromatic Hydrocarbons (PAHs) are widely distributed environmental contaminants of surface and subsurface soils and are listed as priority pollutants. Bioremediation is thought to be the primary mechanism of removal of PAHs in soil systems but biodegradation is largely limited by their low bioavailability. Recent studies show that (bio)surfactants are effective in enhancing the biodegradation of PAHs. Unfortunately, the direct application of (bio)surfactant to soil is unaffordable due to their high operation cost. Our previous study indicated that biosurfactants produced from an isolated strain, Acinetobacter calcoaceticus BU03 effectively promoted the biodegradation of PAHs in aqueous and slurry systems. In the present study, soil spiked with PAHs was composted with pig manure with the inoculation of BU03 in a thermophilic composting system with the purpose to enhance the removal of PAHs from artificially contaminated soil. The Control treatment did not receive any organic amendment while other treatments were amended with/without pig manure and then received different combinations of additions, including BU3 inoculum and/or a PAH degrading strain, Bacillus sp. B-UM, as well as the addition of chemical surfactant or biosurfactants. Within the experimental period of 42 days, the removal ratio of phenanthrene (PHE) and benzo(a)pyrene in the Control were 71.2% and 16.4%, respectively. While in all of the treatments with pig manure amendment, more than 98% of PHE was removed and no obvious difference among treatments was noted. However, the removal ratio of benzo(a)pyrene differed significantly among various treatments. The addition of biosurfactants from BU03 or the inoculation of B-UM increased the removal of benzo(a)pyrene. Furthermore, the co-application of B-UM and BU03 or biosurfactants from BU03 enhanced the degradation of benzo(a)pyrene by 79.3% and 60.0%, respectively. Monitoring of the PAHs degrading microorganisms indicated that both the application of biosurfactants from BU03 and the inoculation of BU03 increased the population of PAHs degrading microorganisms in soil. The present study confirmed that direct application of biosurfactants producing strain provided a more effective and economic means for remediation of PAH contaminated soil.

Figure1. The removal of benzo(a)pyrene. Symbols: Left, Control without organic amendment (); pig manure (PM) only (); PM and biosurfactants (BS) (); PM and B-UM (UM) (£); PM, UM and tween80 (). Right: Control without organic amendment (); PM, UM and BS (); PM, UM and BS, BS inoculated on day 14(); PM, UM and BU03 (£);PM, UM and BU03, BU03 inoculated at day 14().

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