Adsorptive fouling of organic solutes simulating sweetwater solutions on ultrafiltration membranes

• The adsorptive fouling of long chain organic solutes simulating sweetwater solutions was carried out.
• It shows that severe fouling due to solutes deposition and oily layer formation on the surface.
• It reveals that solution plus TG experienced higher RFR compared to TG–FA mixtures.
• Reducing the pH will make the oil droplets and FA agglomerate and coalesces.
• Increasing the pH will promote the saponification between the fat and hydroxide.

One of the major drawbacks for the success of ultrafiltration (UF) during pretreatment of glycerine-rich solutions (known as sweetwater) is membrane fouling due to the deposition of triglycerides (TGs) and fatty acids (FA). The aim of the present study was to contribute to the better understanding of fouling by TG as well as TG–FA mixtures and their adsorption properties on UF membranes. Two UF membranes were used with the membrane materials made from polyethersulfone (PES) and polyvinylidenefluoride (PVDF) with molecular weight cut-off (MWCO) between 5, 20 and 25 kDa for PES, and 30 kDa for PVDF. Static adsorption of TG and TG–FA was investigated at the solution pH values of 3, 7 and 10 for different MWCO. The addition of TG to the glycerine–water solutions caused a significantly higher relative flux reduction (RFR) than TG–FA mixtures, and this was probably due to the formation of macromolecules on the membrane surface. The RFR was also dependent on the MWCO and solution chemistry. Adsorption behaviour onto membrane surfaces was analysed by contact-angle and Fourier Transform Infrared (FTIR) measurements, as well as by Scanning Electron Microscopy (SEM) images. Overall, the results revealed that PES membrane exhibited severe fouling and much larger water RFR than PVDF due to its hydrophobicity and surface roughness.