Colloidal biliquid aphron demulsification using polyaluminum chloride and density modification of DNAPLs: optimal conditions and common ion effect

Abstract

Dense non-aqueous phase liquids (DNAPLs) entrapped and pooled in aquifers serve as a long term source of groundwater contamination because of their low solubility and high density. Density modification displacement (DMD) with colloidal biliquid aphrons (CBLAs) is a promising approach to prevent DNAPL downward migration during surfactant-based remediation processes. CBLA demulsification and quick release of internal light organic matter is the key to density modification of DNAPLs. In this work, it is reported for the first time that polyaluminum chloride (PAC) could destabilize CBLAs efficiently. The optimum conditions for demulsification of CBLAs by PAC were obtained; the effects of several specific ions in groundwater on demulsification of CBLAs by PAC were investigated. The results indicated that the CBLA was completely demulsified by PAC within 10 minutes and released light organic matter. It recorded the highest demulsification efficiency when the addition ratio (V_PAC/V_CBLA) was 2 : 1, concentration of PAC was 0.7 g L⁻¹ and the PVR of CBLAs was 8. Most cations (sodium, magnesium and calcium ions) had inhibitory effects on demulsification of CBLAs by PAC with increasing ion concentration, but iron ions had no effect on it. Sulfate anions showed a stronger inhibitory effect on demulsification of CBLAs by PAC compared to chloride ions. With PAC as the demulsifier, CBLAs could be demulsified efficiently, irreversibly modifying the density of trichloroethylene in 5 minutes.