Q2. What is the effect of water permeating across the active layer?
Water permeating across the active layer dilutes the draw solution in the support layer, resulting in dilutive ICP, the effect of which is to decrease the net osmotic driving force.
Q3. What was deliberately introduced to the water and reverse salt flux readings?
To simulate uncertainty in experimental measurements, errors ranging from 0 to 15% were deliberately introduced to the water and reverse salt flux readings.
Q4. What is the effect of the CV of Jw/Js on the predicted membrane properties?
As the CV of Jw/Js approaches zero, the normalized parameters converge towards unity (horizontal dashed line), signifying the membrane properties are more accurately predicted.
Q5. Why was the draw solution diluted throughout the experiment?
Due to both the permeation of water and the salt leakage, the concentration of thedraw solution was diluted throughout the experiment.
Q6. What is the common method used to calculate the membrane properties in FO?
The least-squares non-linear regression method presented here utilizes an over-determined system of equations to calculate the membrane properties in FO.
Q7. How can the membrane characteristic parameters be determined numerically?
The membrane characteristic parameters can be determined numerically by solving a system of equations if all the other variables, water and salt flux, feed channel mass transfer coefficient, salt diffusivity, and concentrations or osmotic pressures of the solutions, are known.
Q8. How long did the membrane remain in the precipitation bath?
The support membrane remained in the precipitation bath for 10 min before being transferred to a DI water bath for storage until polyamide (PA) formation.
Q9. What is the effect of the reverse flux selectivity on the membrane properties?
Constancy of the reverse flux selectivity between the characterization stages gives not only better prediction of membrane parameters, but also enhances the fit of the calculated fluxes to the experimental readings.
Q10. What is the importance of a consistent method to characterize FO membranes?
A convenient and consistent methodology to characterize FO membranes is of critical importance to advance this technology onto its mature phase, facilitating the sharing of data, their interpretation, and comparison.
Q11. What is the effect of the osmotic pressure and salt concentration difference across the membrane?
The osmotic pressure and salt concentration difference across the membrane increased and, as a result, both the FO water flux and the reverse solute flux augmented to reach values Jw,2 and Js,2, respectively, in stage 2.
Q12. What are the parameters used to determine the membrane properties?
The simulated fluxes (offset by random errors), along with the corresponding draw and feed solution osmotic pressures and concentrations, were input into the Excel algorithm described in Section 3 to determine the membrane parameters A, B, and S that best fit the simulated Jw and Js “measurements”.
Q13. What was the hydrodynamic condition at the stirred boundary layer on the feed side?
In addition, the approximation was justified by the hydrodynamic conditions maintained at the stirred boundary layer on the feed side, where typical values of the feed solution mass transfer coefficient, k, far exceed the permeating water flux.
Q14. Why was the draw solution deviating from the ideal behavior at high concentrations?
Although the sodium chloride draw solution deviates from ideal behavior at high concentrations, this relation was applicable for the procedure outlined here because the solute concentration at the support/ active layer interface was significantly lower than that of the bulk solutions, due to the effects of ICP.
Q15. What is the importance of achieving good CV and R2 values concurrently?
An examination of the figure shows that attaining good CV and R2 values concurrently is essential to minimize errors in the determined parameters.
Q16. How was the whole composite deposited in the precipitation bath?
The whole composite was immediately immersed in a precipitation bath containing 3 wt% DMF in deionized (DI) water at room temperature to initiate non-solvent induced phase separation [41,42].
Q17. How can the authors ensure that the CV of the Jw/Js values lies below 3%?
The authors recommend a CV within 10% to confidently continue theanalyzed by the simulations described in Appendix D. (A) Simulated parameters, A, of variation for Jw/Js values of the different stages in each experiment (a value of f the average error of each simulated parameter, A, B, and S (blue, red, and green, nd salt (orange) fluxes, for chosen ranges of coefficient of variation obtained during ariation requirements is also reported on top of each set of histograms.
Q18. What was the deviation of the calculated values for the reverse salt fluxes?
The deviation of the calculated values was especially pronounced for the reverse salt fluxes, where the higher reverse flux selectivity (A/B) determined for TFC membranes using the RO-FO method (Table 2) resulted in predicted salt fluxes that are significantly lower than the experimental FO values (Fig. 3(E), (G), and (H)).