Using intrinsic bioremediation for petroleum–hydrocarbon contaminated groundwater cleanup and migration containment: Effectiveness and mechanism evaluation

Abstract

Intrinsic bioremediation (IB) is the major mechanism causing the containment of petroleum hydrocarbons in groundwater. The effectiveness and mechanisms of IB on the contaminant removal were evaluated in this study. Groundwater was analyzed for the efficiency of IB, dominant bacteria, bacterial diversity, and biodegradation rates. Concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX) and methyl tert-butyl ether (MTBE) dropped from 6.5 and 0.14 mg/L in source area to 67 and 19 µg/L at the 145 m downgradient area. The biodegradation capacities for BTEX (50.9 mg/L) and MTBE (58.5 mg/L) were higher than the BTEX (6.5 mg/L) and MTBE (0.14 mg/L) concentrations within the plume. The bacterial diversities were assessed by 16S rRNA-based denatured gradient gel electrophoresis and nucleotide sequence analyses. More than 21 petroleum–hydrocarbon biodegrading bacterial species were detected in groundwater indicating that contaminants could be biodegraded by natural-occurring bacteria. The calculated MTBE and BTEX first-order decay rates were 5.7 × 10−4 and 1.3 × 10−3 per day, respectively. The high decay rates indicate that IB mechanisms played important roles in contaminant removal. The observed evidences of IB processes in highly contaminated areas included: (1) decreased electron acceptors, (2) production of degradation byproducts, (3) increased microbial populations and alkalinity, and (4) decreased electron donors and pH.