Intrinsic and enhanced biodegradation of polyaromatic hydrocarbons in aqueous and soil systems

Abstract

Bioremediation is currently one of the most popular methods for remediating soil and groundwater contaminated by organic compounds. However, it has been found that the availability of the target contaminant to the microbial populations capable of degrading the compound may serve as a limiting factor in many systems. Thus, there is interest in the use of solubilization agents for enhancing bioavailability of organic contaminants. The impact of hydroxypropyl-β-cyclodextrin (HPCD) on the biodegradation of polycyclic aromatic hydrocarbons (PAHs) was investigated in a batch study. Results showed that HPCD can significantly increase the apparent solubility of phenanthrene, which had a major impact on the biodegradation rate of phenanthrene. For example, in the presence of 10⁵ mg L⁻¹ HPCD, the substrate utilization rate increased 5.5 times and only 0.3% of the phenanthrene remained at the end of a 48-hour incubation. It strongly suggests that HPCD can significantly increase the bioavailability, and thereby enhance the biodegradation, of phenanthrene. Biodegradation is often of great importance for the transport, fate, and remediation of organic contaminants in the subsurface. When modeling biodegradation processes, it is usually assumed that the microbial population responsible for biodegradation is composed of a single species. However, this is unlikely to be true for many, if not most, field situations. The effect of multiple species of degraders on phenanthrene biodegradation and transport in a saturated soil (with a high phenanthrene sorption capacity) was evaluated with a series of miscible-displacement experiments. Breakthrough curves obtained for the non-sterile column experiment exhibited oscillations in microbial populations as well as in oxygen and phenanthrene concentrations during the 6 months of continuous injection of a constant-concentration phenanthrene solution. This behavior is due to the response of the heterogeneous bacterial population (24 species) to substrates and oxygen availability, wherein population dynamics is hypothesized to be mediated by competition and other multi-species interactions. The dynamics of heterogeneous microbial populations, especially under growth conditions, should be considered when evaluating contaminant biodegradation and transport in natural subsurface systems.