Impact of organic matrix compounds on the retention of steroid hormone estrone by a 'loose' nanofiltration membrane
The impact of solute–solute interactions on retention and membrane adsorption of the micropollutant estrone was determined in the presence of surfactant sodium dodecyl sulphate (SDS), natural organic matter (NOM) and cellulose. A five cycle stirred cell protocol was used to study progressing saturation of a loose nanofiltration membrane with estrone. Adsorption was absent at high pH when the estrone molecule was dissociated, while at low and neutral pH the membrane was saturated after three filtration cycles and breakthrough was obvious. Increased estrone retention in the presence of cellulose was observed due to estrone–cellulose partitioning. SDS and NOM reduced estrone retention at low and neutral pH while no significant effect was visible at alkaline pH when solute–solute interactions were minimal. The adsorption and deposition of estrone onto the membrane was up to 50% of the total estrone in solution. Using experimental partition coefficients, the mass of estrone sorbed to organic matter as a function of pH was estimated. Results were similar to the total mass of estrone adsorbed to the membrane despite the partition coefficients being quantified at equilibrium (24 h) while the experiment was (naturally) not. This study provides first quantifiable evidence of the impact of micropollutant–organic matter interactions in membrane filtration.