A study of cloud point extraction for removal of aromatic contaminants from wastewater

Abstract

Cloud point extraction (CPE) has been successfully scaled up to continuously remove aromatic contaminants from wastewater in a multi-stage rotating disc contactor. When the nonionic surfactant solution has a temperature higher than the cloud point, phase separation occurs, forming the coacervate phase, and the dilute phase. Most of contaminants contained in the wastewater will solubilize into the surfactant micelles and concentrate in the coacervate phase, thus the dilute phase can be discharged as treated water. The extraction performances for removal of organic solutes with difference structures and initial concentrations were compared for both batch and continuous CPE. The higher the Kow (octanol-water partition coefficient) or hydrophobicity of solutes, the better the extraction due to the greater affinity of solutes to solubilize into micelles. The empirical linear correlations between log Kow, log (solute partition ratio), and log (height of transfer unit) were developed. The extraction ability decreases as the initial concentration of solute in the wastewater increases mainly due to the coacervate entrainment into the overhead effluent. In addition, the effect of nonionic surfactant molecular structure on the CPE of phenol in batch experiment was studied. Phenol coacervate solubilization equilibrium constant is shown to increase linearly with EO number, but is unaffected by alkyl carbon number or hydrophobe branching. A model is developed which can predict the phenol partition ratio at a given temperature for any AE surfactant structure dependent on only one simple measured parameter: fractional coacervate volume. Finally, potential solutions for surfactant entrainment in the dilute phase after CPE were proposed and studied.