Alleviating membrane fouling of modified polysulfone membrane via coagulation pretreatment/ultrafiltration hybrid...

In this study, ultrafiltration membrane fouling was alleviated by hydrophilic modification and coagulation pretreatment. A polydopamine (PDA) layer was used as a bridge to introduce the nano titanium dioxide (TiO₂) onto the polysulfone (PSf) membranes, forming a hydrophilic modified layer. A relationship model was established between the coagulation efficiencies and floc properties and membrane fouling of the modified PSf membranes during the coagulation/ultrafiltration (C-UF) process. The combination styles of flocculants, poly dimethyldiallylammonium chloride (PDMDAAC) and polyaluminum chloride (PAC) were used in C-UF hybrid process. The characterization results indicated that the hydrophilicity was significantly enhanced in the modified PSf membranes. Scanning electron microscopy (SEM) tests proved that the PDA layer could be tightly bound to TiO₂ by coordination bond onto PSf membrane surface. In the acidic conditions, more TiO₂ nano-particles were adhered on the PDA particles surface as the pH of (NH₄)₂TiF₆ solution was increased, which resulted in higher hydrophilicity of membranes. In addition, the C-UF tests exhibited that the coagulation efficiency was greatly improved in the PAC/PDMDAAC system, and the PSf membrane modified by PDA/TiO₂ in UF tests significantly reduced the membrane fouling, this was partially due to the formation of TiO₂ modified coating with higher hydrophilicity.