Potential of ceramic ultrafiltration membranes for the treatment of anionic surfactants in laundry wastewater for greywater reuse

Abstract

Decentralized greywater treatment is gaining increasing recognition as an alternative for natural water supplies. Laundry wastewater in relatively large amounts of greywater is considered as a valuable resource with high reuse potential. However, organic pollutants with low molecular weights (e.g., anionic surfactants) that originate from laundry additives should be effectively removed. Because anionic surfactants are widely used to produce detergents, the retention of sodium dodecylbenzene sulphonate (SDBS; a typical anionic surfactant in laundry wastewater) was evaluated with a bench-scale ceramic ultrafiltration (UF) membrane filtration system. The results demonstrate that SDBS can be successfully retained with a ceramic UF membrane with a nominal pore size of 1 kDa (~4.0 nm) by carefully controlling several operating parameters. The dynamic phase changes of the surfactant that depend on its concentration affect the SDBS retention performances regardless of the operating parameters. At a high transmembrane pressure (TMP) and room temperature, the SDBS micelles that form on the membrane surface cause a pre-sieving effect induced by concentration polarization, thereby increasing the SDBS retention. As the solution pH increased, electrostatic repulsion between the solute and membrane surface induced higher SDBS retention rates. The retention rate also increased significantly with increasing ionic strength, which was especially pronounced with divalent ions than with monovalent ions because higher ion specificity could reduce the charge repulsion and induce their micellization. These electrostatic and adsorptive interaction could demonstrate a better understanding of surfactant retention mechanisms. Consequently, ceramic UF membranes have the potential of treating laundry wastewater attaining moderately high concentrations of surfactants.