Mass-transfer modeling of reverse-osmosis performance on 0.5-2% salty water

This work investigates the desalination efficiency from 0.5 to 2% salty water using the RO process and establishes mass-transfer models for water and salt transports. The water flux, salt passage rate, salt rejection and water recovery were studied under various operating conditions to validate the model adequacy. Salt permeability in the three-layer composite was lower than that predicted on polyamide-polysulfone top-intermediate layer using permeation cells, possibly due to the membrane compaction at a high pressure and/or additional mass-transfer resistance from the non-woven support. The permeate flux was 1.83-3.67×10^-5m³m^-2s^-1 for 0.5-2% NaCl feed solution, significantly higher than literature data. The salt concentration was reduced to 350-700ppm from 1 to 2% NaCl solutions, rendering salt rejections of 91.0 to 98.4% under the tested operating conditions. The membrane intrinsic retention was 96.1 to 99.8% considering the increased solute concentration adjacent to the membrane surface resulting from concentration polarization phenomena. The salt flux did not show a particular trend with respect to the permeate flux resulting from various applied pressures, indicating a negligible flux coupling effect between the water and salt molecules. The salt transported mainly through solution-diffusion mechanism and water flow followed a pressure-driven process.