Membrane fouling mitigation for enhanced water flux and high separation of humic acid and copper ion using hydrophilic polyurethane modified cellulose acetate ultrafiltration membranes

The presence of both copper ion (Cu (II)) from industry and humic acid (HA) in natural waters may generate Cu (II)–HA complex, which is a non-biodegradable and toxic organic pollutant in the water. Removal of such toxic substance is of great importance and environmental significance. Although membrane technology provides a solution for the removal via the filtration, fouling still presents a major challenge for the effective separation. In this study, polyurethanes endcapped with β-cyclodextrin and lactic acid were synthesized and used as additives to be blended with cellulose acetate membranes, which possessed enhanced hydrophilicity, permeability and antifouling property for the removal of Cu (II) and HA. As an example, the polyurethane endcapped with lactic acid (LPU-CA) membrane exhibited high pure water flux (PWF) of 648 L m⁻² h⁻¹, as well as high flux recovery ratios (FRRs) of 97.8% and 92% and low irreversible fouling rate (F_ir) of 2.2% and 7.8% for the ultrafiltration (UF) of HA and Cu (II)–HA complex, respectively, showing excellent anti-fouling performance. In addition, the Cu (II) and HA rejection was greatly enhanced by the HA enhanced complexation process. These results indicated that the polyurethanes modified cellulose acetate membrane provided enhanced separation with good antifouling property, which can be potentially used for the cleaning of the toxic metal-organic pollutants in wastewaters.