Use of coacervate phase to extract the aromatic solutes from wastewater by using a nonionic surfactant

Abstract

The cloud point extraction (CPE) of aromatic contaminants (benzene, toluene and ethylbenzene) from wastewater was studied as batch experiments in laboratory scale and continuous operation in a pilot scale, differential extracotr. An environmentally friendly nonionic surfatant was utilized as a separating agent. When the temperature of the nonionic surfactant micellar solution is greater than its cloud point, the solution will separate into two aqueous phases known as the micellar-rich phase or coacervate phase, and the micellar-dilute phase. The organic solutes contained in the solution tend to solubilize into the micelles and mostly concentrate into the coacervate phase, leaving the dilute phase with a low concentration of solutes as the purified water. In batch experiments, several vials capped with septa containing nonionic surfactat, aromatic solute, and water with and without added electrolyte (NaCl) were placed in an isothermal water bath until equilibrium was reached. After phase separation occurred, the relative phase volumes of each phase were measured. The concentrations of nonionic surfactant and aromatic solute in the micellar-rich phase and the micellar-dilute phase were analyzed. The results showed that temperature, NaCl concentration and degree of alkylation of the aromatic solutes enhance the solute partition ratio, leading to a higher solute concentration in the micellar-rich phase. In continuous operation, a pilot scale, temperature controllable rotating disc contactor (RDC) was fabricated. The polluted water and nonionic surfactant solution were fed counter-currently to the column as feed and solvent, respectively. The phase separation occurred inside the column. The concentrations of nonionic surfactant and aromatic solute in the coacervate stream and the micellar-dilute phase stream were analyzed. The concentration of solute in the coacervate phase increases as temperature, rotation speed of the rotor disc, NaCl concentration, wastewater/surfactant solution flowrate ratio and degree of alkylation of the aromatic soutes increase. The overall volumetric mass transfer coefficient and the number of transfer unit in the RDC increase with increasing temperature and rotation speed of the rotor disc. In pilot scale, multistage, continuous extractor, the toluene partition ratio and concentration of toluene in the coacervate phase are two times greater than that observed in a single stage, equilibrium batch experiment with the same initial condition.