Purification of Phenolic-Laden Wastewater from the Pulp and Paper Industry by Using Colloid-Enhanced Ultrafiltration

Abstract

The removal of three phenolic pollutants with variable degrees of chlorination from water was investigated: 2-monochlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP). These compounds are often found in pulp and paper mill wastewater effluent. Colloid-enhanced ultrafiltration (CEUF) techniques were investigated for wastewater purification. Pollutants can associate with colloids: surfactant micelles or surfactant–polymer complexes solubilize nonionic compounds. In this application of CEUF, the micelles or surfactant–polymer complexes are ultrafiltered from solution with solubilized chlorinated phenol pollutant. An advantage of surfactant–polymer complexes, compared to only surfactants, is reduction of surfactant monomer (unaggregated surfactant) concentration. These surfactant monomers can pass through the ultrafiltration membrane, reducing the purity of the product water. Excellent solute rejections are observed for both micelles and surfactant–polymer complexes, generally exceeding 90% for DCP and TCP, even exceeding 99% in some cases. The ratio of the solubilization constant in micelles to that in surfactant–polymer complexes varied from approximately 1 to 5. In micelles, rejection increases in the orderMCP<DCP<TCP, whereas in the surfactant–polymer system, rejection of the DCP and TCP can sometimes reverse order. The surfactant monomer leakage into the permeate for the surfactant–polymer system is only about 1 to 10% of that for the surfactant micelles, down to very low concentrations approaching 1 μM. Therefore, CEUF using surfactant-only or surfactant–polymer mixtures can be a very effective separation technique to remove chlorinated phenols from wastewater. Surfactant–polymer systems result in lower surfactant leakage, but somewhat poorer rejections of the pollutant. It is anticipated that it will be more difficult to recover the colloid for reuse compared to use of a pure surfactant.