Influence of trace cobalt(II) on surfactant fouling of PVDF ultrafiltration membrane

Abstract The influence of trace cobalt on membrane performance was investigated during ultrafiltration of surfactant-containing wastewater. The most serious membrane fouling occurred in cationic surfactant solution due to its higher affinity with membrane surface. With an increase of cobalt concentration, the flux decreased faster and membrane fouling became more serious, especially for ionic surfactant solutions. Using Hermia’s blocking models, the membrane fouling varied from standard pore blocking and intermediate pore blocking (0–1 mg/L cobalt) to cake filtration (5 mg/L cobalt). The presence of Co probably promotes fouling via two mechanisms: 1) By reducing the CMC so that micelles form more readily, which promotes size exclusion. The micelles were more easily adsorbed and rejected by the membrane, leading to more extensive membrane fouling and higher rejection of surfactants. 2) By regulating the electrical charge of micelles to be more positive so that the micelles are more easily adsorb onto membrane through electrostatic effect. Rejection and deposition of cobalt both increased in the presence of surfactants, especially higher in anionic surfactant solutions. In conclusion, the complexation of cobalt and surfactants strongly influenced ultrafiltration performance, which should be carefully considered in membrane treating wastewater containing surfactants and trace transition metals.