Comparative Assessment of Regular and Persulfate Oxidative Foams in Air Sparging for Trichloroethylene Dense Nonaqueous Phase Liquid Remediation.

This study investigated the feasibility of foam-enhanced air sparging (FEAS) for remediating trichloroethylene (TCE) dense nonaqueous phase liquid (DNAPL) in water. Various surfactants, including polyoxyethylene (20) sorbitan monooleate (TW80), sodium dodecyl sulfate (SDS), sodium α-olefin sulfonate (AOS), and TW80/SDS and TW80/AOS combinations, were used to generate foam, which were evaluated for foam stability and quality. AOS (32 mM) exhibited the highest foam stability (∼345 min) and quality (∼99.6%) under controlled conditions. Phase contrast microscopy analysis showed foam sizes of 290-400 μm with thin film thicknesses of 6-9 μm. FEAS was tested with and without sodium persulfate (SPS) oxidant (oxidative foam) to treat approximately 10 g of TCE DNAPL in 1 L of water. Injecting AOS foam (32 mM) or oxidative foam AOS (32 mM)/SPS (50 or 1700 mM) for 2 h dissolved 60-82% of TCE, compared to only 4-7% with N2 injection. The surfactant-stabilized interface in foam facilitated TCE adsorption, increasing its partitioning into bubbles, leading to enhanced volatilization. In the lamella region, surfactant layers promoted TCE dissolution, while SPS aided its mineralization. With oxidative foam at a higher SPS concentration (1700 mM) and an extended reaction time (240 h), TCE mineralization increased to 40-74% across different foam injection rates. These results highlight oxidative FEAS as a promising improvement over conventional air sparging, significantly enhancing TCE dissolution, volatilization, and oxidation.