| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 97 === Soils which are long term contaminated with petroleum hydrocarbons usually encountered with problems of high residual concentrations and usually require a relatively long remediation time. The reason can be the lag phase observed during the remediation course, as well as the difficulty of natural TPH degradation during the second-stage remediation process.
The objective of this study was to establish a two-stage bioremediation strategy to remediate an aged hydrocarbon-contaminated soil. The purpose of the strategy was to reduce the time taken for the 1st-stage degradation, and to efficiently transfer the system to the 2nd–stage, with the purpose of achieving the remediation goal and improving the problem of the residual concentrations.
The soil contaminated by 14,032 mg total petroleum hydrocarbon (TPH) /kg dry soil was employed in the study to find an optimal bioremediation approach. The bioremediation approach of combined bioaugmentation and biosurfactant, with introduction of five strains bacteria of 108 CFU/g dry soil and 100 mg/kg soil of rhamnolipid (A8R100), reached the first stage of degradation in 35 days and removal efficiency of 70%. The problem of slow TPH degradation found to be related to the polar fractions accumulation. Increase of fungi community diversity was found helpful in decomposition of the polar fractions. The symbiotic environment between bacteria and fungi was beneficial to the 2nd –stage TPH biodegradation.
Based on the above findings, we designed a two-stage remediation strategy, by using the A8R100 approach during the 1st stage. Then, when TPH was persistent to be further degraded, we enhanced the fungi diversity in the remediation system in order to shorten the lag phase and to improve the degradability particularly for the polar substances. Our result indicated that, with the A8R100 approach, the soil initially contaminated with 7,379 mg TPH/kg dry soil could complete the 1st – stage degradation by the 1st 21 days, and the removal efficiency was 65%. We then added hydrocarbon degrading fungi and yeast in the second-stage, and the removal efficiency was raised to be 87% and 89%, respectively. When the compost kitchen waste (KW) strategy was employed, the TPH removal efficiency was higher than 89%.
The two-stage bioremediation strategy could help us to attain the Taiwan Soil and Groundwater Remediation Regulation, TPH lower than 1,000 mg/kg dry soil, within three months. The application of fungi and kitchen waste found to be useful in shorten the lag phase during the 2nd-stage degradation and achieve the remediation goal efficiently.
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