Characterization of subsurface petroleum contaminants and their chemical and biological remediation with redox manipulation.

Abstract

The research presented in this dissertation has examined the bioremediation of subsurface petroleum contamination. Three aspects have been studied, i.e., quantitative characterization of petroleum contaminants, aerobic biodegradability of these contaminants following a prior oxidant intervention, and evaluation of the performance of in situ redox manipulating technologies (e.g., permeable reactive barrier technology) for (bio)remediation of these contaminants. Equivalent carbon number (EC)-based hydrocarbon fractions and a fraction-specific GC/MS method were established and developed. Comparison of this GC/MS method with commonly-used inexpensive rapid field screening methods was examined. Reductive redox capacity (RDC) was correlated with total petroleum hydrocarbons (TPH). The results suggest that inexpensive field screening techniques coupled with EC-based fraction-specific GUMS determinations can reduce the cost of site screening and remedial action design. Biodegradability of JP-4 jet fuel was studied using a sequential chemical and microbial oxidation scheme with three oxidants (KMnO₄, H₂O₂, and MgO₂) applied to the chemical oxidation. The mechanisms of TPH and EC-based fractions' degradation and toxicity reduction were explored for a two-step chemical and biological oxidation process. The pseudo-first rate constants for both chemical and biological oxidation processes were estimated. The results suggest that strong oxidants (i.e., KMnO₄ and H₂O₂) directly degraded TPH and selected EC fractions, reducing both fuel mass and toxicity. MgO₂ appeared to accomplish little or no direct oxidation, rather it enabled subsequent microbial degradation. The performance of permeable reactive barrier (PRB) technologies for in situ bioremediation of petroleum contaminants was evaluated by modeling the dissolution or release process of barriers as diffusion controlled. A transient model was proposed to simulate the dissolution and the transport of injected reductants and oxidants. The in-situ lifetimes and kinetics of the barriers were estimated.