Adhesion forces between humic acid functionalized colloidal probes and polymer membranes to assess fouling potential

Abstract

Fouling of membrane surfaces by organic, inorganic and biological materials is a significant cause of increased operational costs and power consumption for membrane separation processes including reverse osmosis, nanofiltration, membrane bioreactors and membrane distillation. Novel polymeric membrane surfaces are being developed by numerous research groups to counter foulant attachment and build up. One such type of membranes under development are ones which contain an active surface created using polymeric bicontinuous microemulsions (PBM) [1]. In this work we use humic acid functionalised colloidal probes to simulate organic foulants to investigate the adhesion forces between polymer membranes modified with a PBM coating, both in high purity water and model textile dye wastewater (MTDW). Membrane performance varied considerably when comparing different preparations and with the commercial PES membrane which was used as the base-layer. When making measurements in the two liquid media it was found that the behaviour was very different, with some membranes showing low adhesion in water showing high adhesion in the textile dye wastewater and vice versa. Water contact angle measurements of clean membranes showed good correlation with measured adhesion forces. Conversely, contact angle measurements made with membranes after prolonged exposure to MTDW showed a strong inverse correlation with the measured adhesion forces in MTDW, with more hydrophilic surfaces showing greater adhesion with the functionalised probe. Measurements of contact angle of humic acid before and after exposure to MTDW showed a change from a hydrophobic substance (129°) to a moderately hydrophilic substance (29°). These measurements suggest that the modification of both membranes and probe by components in the MTDW changed the adhesion forces experienced by the HA probe from favouring hydrophobic interactions to hydrophilic ones.