Date of Award
Doctor of Philosophy (PhD)
Civil and Environmental Engineering
W. David Constant
Kalliat T. Valsaraj
Surfactant based processes are emerging and becoming increasingly important in pollution control. A novel predispersed solvent extraction (PDSE) technique using surfactant based colloidal liquid aphrons (CLAs or polyaphrons) and colloidal gas aphrons (CGAs) for the removal of hydrophobic organic compounds (HOCs) from the aqueous phase was studied. The process involves an extraction of HOCs into CLAs, followed by a flotation using CGAs. Polyaphrons were characterized by a particle size analyzer. The size distribution was found to be bimodal. The effects of surfactant types, surfactant concentrations and storage times on the size distribution were studied. Polyaphrons have long shelf-lives and are dynamically very stable when dispersed in water. Flotation of polyaphrons was deduced to be the result of electrostatic forces between CGAs and polyaphrons. Semibatch PDSE experiments showed that the efficiency of a dye (Solvent Red 27) removal depended not only on the duration of flotation but also on the retention time after flotation. A mathematical model for a continuous countercurrent PDSE process was developed and tested using experimental data. The model predicted that the process efficiency is a function of the flowrates of CGAs and polyaphrons relative to feed water flowrate, the partition coefficient of the solute, relative sizes of polyaphrons to CGAs, and the attachment efficiency of polyaphrons to CGAs. The PDSE process is at the expense of residual surfactants in the effluent water. Therefore, batch shaker-flask experiments were conducted to study the aerobic biodegradation of surfactants and surfactant-laden HOCs in a wastewater collected from a local Superfund site. Results on four commercial surfactants showed that linear primary alkyl sulphates (sodium dodecyl sulfate, SDS) and linear primary alcohol ethoxylates (Witconol) exhibited better biodegradation potential than linear primary alkylbenzenesulfonates (sodium dodecylbenzenesulfonate, SDBS) and linear secondary alcohol ethoxylates (Tergitol). Increased surfactant concentrations above the critical micellar concentrations (CMCs) showed inhibitory effects, lower biodegradability and foam degradation. A plant based natural surfactant (Ritha) performed better than commercial surfactants in terms of biodegradability at concentrations above CMC, but exhibited poorer foam degradation. Results indicated that surfactant-laden HOC effluent is nutrient-limiting. Addition of surfactants also enhanced the biodegradation of HOCs.
Zhang, Chunlong, "Removal of Hydrophobic Organic Compounds and Surfactants From Wastewater: Polyaphron-Enhanced Solvent Extraction and Biodegradation." (1997). LSU Historical Dissertations and Theses. 6455.