Two-liquid-phae bioremediation of soil contaminated by hydrophobic organic compounds

Abstract

Recently, two-liquid-phase (TLP) bioremediation has been studied as an alternative method to the surfactant-enhanced bioremediation for treatment of soil contaminated by hydrophobic organic compounds (HOCs) with poor bioavailability to microorganism. Overall mechanisms of TLP bioremediation for removal of contaminants consist of desorption from soil, mass transfer to water-immiscible liquid (WIL), and biodegradation. This dissertation focused mainly on the understanding of these mechanisms with various experimental parameters. Studies were conducted to observe the solubility of phenanthrene, anthracene, and pyrene in four WILs and the mass transfer of PAH in a TLP system. The order of solubility in WILs for three different PAHs was phenanthrene > pyrene>> anthracene. Among the WILs tested in a TLP system, paraffine oil did not affect the mass transfer of three PAHs, while silicone oil reduced the mass transfer of anthracene significantly because paraffine oil had a higher solubilization capacity for anthracene than silicone oil. When initial PAH concentration increased up to 2500 mg PAH/kg soil, the mass transfer of phenanthrene and pyrene were hardly influenced, while that of anthracene was lowered to 40 %. As the amount of light paraffine oil decreased, the mass transfer of anthracene decreased considerably compared to that of phenanthrene and pyrene. Based on the present results, it was confirmed that the mass transfer of PAHs from soil to WIL was governed mainly by the solubilization capacity of WIL for PAHs. A two-liquid-phase bioreactor (TLPB) was employed to study the degradation of phenanthrene, anthracene, and pyrene using Sphingomonas sp. 3Y. Among three PAHs, most of phenanthrene was degraded very rapidly within 5 days and anthracene was also degraded simultaneously with phenanthrene. Pyrene was not biodegraded during the short period of the TLPB operation, but it was removed almost completely from soil by mass transfer. The degradation efficiencies ...