Rejection of small charged and uncharged organic pollutants in reverse osmosis of salty and seawaters

Two organic solutes of close molecular weight (approximate to 270 g mol(-1)) and hydrophobicity (logK(ow) approximate to 1.2- 1.5) were selected as model micropollutants to study their reverse osmosis in seawater. Tropaeolin O can be a monovalent/divalent anion whereas Thiamine can be a monovalent/divalent cation. Their charges and hydrophilic/hydrophobic balance can be modulated by playing on the pH and the ionic strength. The TFC-HR (Koch, USA) and SW30 (FilmTec, The Netherlands) membranes have shown a similar overall behavior either for single NaCl or Tropaeolin O filtrations. The comparison of Tropaeolin O/Thiamine rejections by the TFC-HR membrane has shown that membrane/solute electrostatic interactions explained the rejection in single solutions. However, in 30 g L-1 NaCl and synthetic seawater, rejections were more likely due to the hydrophobic/hydrophilic balance of a given solute: the more hydrophobic form being more rejected than the hydrophilic ones. Finally, the ethanol addition (30%) was achieved to study the impact of a second concentrated organics, moreover able to modify the background solvent of the filtration; Tropaeolin O rejection was decreased.