Cyclodextrin-enhanced biodegradation of phenanthrene

The effectiveness of in situ bioremediation in many systems may be constrained by low contaminant bioavailability due to limited aqueous solubility or a large magnitude of sorption. The objective of this research was to evaluate the effect of hydroxypropyl-β-cyclodextrin (HPCD) on phenanthrene solubilization and biodegradation. Results showed that analytical-grade HPCD can significantly increase the apparent solubility of phenanthrene. The increase in apparent solubility 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 from 0.17 mg h^-1 to 0.93 mg h^-1 while the apparent solubility was increased from 1.3 mg L^-1 to 161.3 mg L^-1. As a result, only 0.3% of the phenanthrene remained at the end of a 48 h incubation for the highest concentration of HPCD tested (10⁵ mg L^-1). In contrast, 45.2% of the phenanthrene remained in the absence of HPCD. Technical grade HPCD, which contains the biodegradable impurity propylene glycol, also increased the substrate utilization rate, although to a lesser extent than the analytical-grade HPCD. On the basis of these results, it appears that HPCD can significantly increase the bioavailability, and thereby enhance the biodegradation, of phenanthrene.