Doctoral Dissertations

Zhou Shi

Date of Award

8-1998

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Mriganka M. Ghosh

Committee Members

Chris Cox, Kevin Robinson, Michael Essington, Michael Sigman

Abstract

The dissolution and photochemical behavior of 2-chlorophenol (2CP) and polychlorinated biphenyls (PCBs) in micellar surfactant solutions were evaluated. The solubility of all PCBs examined were enhanced in surfactant solutions, even at surfactant dosages below the critical micelle concentration (CMC). However, at supra- CMC dosages of surfactants, the extent of solubility enhancement was much greater, the solubility being linearly related to surfactant concentration up to a dosage of 4 g/L. Nonionic surfactants were more effective than their anionic counterparts in dissolving PCBs. For three nonionic surfactants, polyoxyethylene (POE) lauryl ethers, the apparent solubility of 2,2',4,4'CB was inversely related to the hydrophile-lipophile balance (HLB) or the POE chain length in this case. Further, a linear relationship between Km and Kow was observed for several PCBs in polyoxyethylene (10) lauryl ether (POL (10)) solution. The UV spectra of 2,2',4,4'CB dissolved in micellar POL(10), hexane, and DME were similar indicating that the PCB molecules were possibly located at the micellar core or its vicinity. In 3 days of washing, POL(10) could extract 47-74% Soxhlet-extractable PCBs from two aged, PCB-contaminated soils. Linear Solvation Energy Relationship (LSER) was used to compare the degree of association of 2CP, a relatively soluble chlorophenol, with micelles in nonionic and anionic surfactant solutions. While only 15% of the 2CP molecules was associated with anionic sodium dodecyl sulfate (SDS) micelles, 38% was associated with the micelles of Brij35, a nonionic POE surfactant. Photolysis of chlorinated aromatic hydrocarbons (CACs) was enhanced when dissolved in surfactant solutions. Acting as H-atom donors, surfactants promoted photodegradation rate and quantum yield of CACs, even at sub-CMC dosages. At supra- CMC dosages, formation of surfactant micelles further increased the reaction ability between CACs and surfactant molecules through micellar "cage" effects. The nonaqueous, solvent-like micellar "cage" allowed the reactants and intermediates to remain longer at higher local concentrations inside the micelles. Dechlorination followed by H abstraction from surfactant molecules appeared to be the principal mechansim of photodegradation PCBs in surfactant solutions. In stepwise photodechlorination of PCBs, ortho chlorine atoms were found to be more labile than the para chlorine atoms. For the photolysis of 2CP (pKa=8.5), two pathways were identified. At pH > 8.5, the excited anionic species is dechlorinated to form a singlet carbene that can either be transformed to cyclopentadienecarboxylic acid through a ring contraction via the Wolff rearrangement, or be converted to phenol via a triplet carbene mechanism involving abstraction of two H atoms from an H donor, a surfactant for example. UV-irradiation of undissociated form of 2CP leads to the formation of catechol via a nucleophilic displacement of chloride in the presence of water, while in non nucleophilic media, the 2CP undissociated form was phototransformed to phenol, presumably by homolytic scission of the C-Cl followed by hydrogen abstraction. Phenol was observed to sensitize 2CP photodegradation involving a charge transfer dechlorination reaction. Photolysis of PCBs in surfactant soil-washing solutions is effective, even in the presence of moderately high turbidity. The highly chlorinated congeners that are usually recalcitrant to biodegradation are likely to become biodegradable following photodegradation. Therefore, surfactant washing and photolysis, used in tandem, could be a viable technology for remediation of PCB contaminated soils.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS