NF/RO filtration of the hydrophobic ionogenic com#163 triclosan: Transport mechanisms and the influence of membrane fouling
Filtration phenomena of the hydrophobic ionogenic compound triclosan by three commercially availablenanofiltration (NF)/reverse osmosis (RO) membranes were investigated in this study. The separationbehaviour of triclosan was systematically related to the compound physicochemical properties and themembranes as well as the solution pH. The influence of membrane fouling on the rejection of triclosanby the three selected NF/RO membranes were also examined using three model organic foulants and onemodel colloidal foulants. Having a unique hydrophobic ionogenic profile, even when triclosan was fullydeprotonated at pH 10, considerable adsorption of the compound to the membrane could still be observed.The adsorption of triclosan to the membrane surface was a precursor for the diffusion of this compound through the membrane. In fact, under clean (virgin) membrane condition, considerable diffusive transportof triclosan through the loose nanofiltration NF-270 as well as the tight nanofiltration NF-90 membranewas clearly evident, leading to a lower rejection of triclosan by these membranes than expected basedon their molecular weight cut-off or the size exclusion mechanism. This diffusive transport appears to bedependent on the thickness of the active layer and its porosity. As a result, no triclosanwas detected in thepermeate samples from the reverse osmosis BW-30 membrane which has a thicker and more dense activeskin layer. Results reported in this study also indicate that the formation of a hydrophobic fouling layeron the membrane surface could interfere with the solute membrane interaction, and thus, reduce thediffusive transport of triclosan across the membrane. Consequently, significant enhancement in rejectionof triclosan was observed when the membranes were pre-fouled with the three model organic foulantsnamely bovine serum albumin (BSA), alginate and humic acid used in this study. In contrast, no discerniblevariation in rejectionwas observed when the membraneswere pre-fouled with hydrophilic silica colloidsas compared to the clean membrane condition.