New insights into membrane fouling formation during ultrafiltration of organic wastewater with high salinity

Membrane separation technology has been generally preferred for treating high-salinity organic wastewater during the last decades of years. Despite not suitable for ion removal, ultrafiltration (UF) is quite appropriate and widely employed for retaining solids, organic matters and macromolecules etc. from high-salinity wastewater. However, limited efforts have been made to investigate the UF fouling characteristics affected by such high saline environment. In this study, sodium chloride (NaCl) with the concentration higher than 10 g/L was employed to examine its impacts on the UF fouling behaviors. The results showed that the involvement of high-concentration NaCl remarkably aggravated HA fouling formation, whereas mitigated BSA fouling development. In the presence of NaCl, HA seemed to form a more homogenous fouling layer, while substantial scattered and large NaCl crystals with different shapes appeared on BSA fouling layer. Further analysis demonstrated that NaCl at high levels induced the agglomeration of BSA foulants, leading to their slower transportation to membrane surface and alleviated the formation of cake layer. Comparatively, the electrostatic attraction and thermodynamic interactions between HA-HA and HA-membrane were substantially increased at high-salinity condition, probably facilitating HA migration to membrane and enhancing fouling layer development. Consequently, the different effects of high salinity on HA and BSA fouling were systematically revealed with their formation mechanisms proposed, which should provide an insightful guidance for membrane fouling control when high-salinity organic wastewater is treated with membrane-based technique.