The effect of ionic regulation on the structure of whey protein during ultrafiltration process and hydraulic reverse cleaning efficiency

The effects of ionic regulation on the structure of membrane surface proteins and backwashing efficiency during ultrafiltration were investigated to reveal the mechanism of ionic mitigating membrane fouling. The repulsion between proteins and membrane was enhanced after ion regulation. With the extension of ultrafiltration time, the alpha-helix and random coil of membrane surface proteins were decreased, while the beta- turn structure increased which was subjected to continuous regulation by Na+, Zn2+ and K+ at 4 min, 8 min and 12 min, respectively. Fourier transform infrared spectroscopy and Raman spectroscopy of membrane surface proteins showed that intra- and intermolecular hydrogen bonds of proteins were reduced on membrane surface. The exposed hydrophobic amino acid groups were reduced. The experimental group which was regulated by Na+ Zn2+ and K+ was favourable for the reduction of cake resistance (Rc) and had a lower square roughness (Rq) on membrane surface during filtration process. However, this could lead to the increased pore blockage (Rp), which was not conducive to hydraulic reverse cleaning efficiency compared to the experimental group regulated by K+, Zn2+ and Mg2+. Therefore, regulation of the whey ultrafiltration process by different ions at specific time is helpful in alleviating membrane fouling.