Design of Forward Osmosis Desalination Configurations: Exergy and Energy Perspectives

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this manuscript, the energy and exergy of the FO desalination system is analyzed. The paper has a complete structure and detailed data, especially in the quantitative analysis of energy/exergy. It is recommended to accept after revise.

1. In Figure 1, it is proposed to change to a color diagram to clearly distinguish the components of the desalination system.
2. The font size in Figure 2 is too small to read.
3. The color scheme in Figure 3 is too harsh and somewhat obscuring the font color, so it is recommended to change to a lighter and coordinated color scheme.
4. It is recommended to briefly compare FO and RO to highlight the advantages of FO.
5. It is advisable to discuss the causes of the 57.9 MW exergy loss, e.g. is it caused by the concentration difference? This can provide an in-depth reference for the design of the FO system.
6. What are the operating conditions corresponding to each energy/exergy value? And it is recommended that the author give specific operating conditions.
7. The engineering implications of the conclusion can be further deepened.

Author Response

Response to reviewer 1 is attached.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

It is important that, based on the analysis of exergy, the authors perform a cost analysis based on energy expenditures to demonstrate that energy viability is closely related to economic viability; or, failing that, make a comparison with bibliography that has carried out exergetic and cost analyses at the same time. Since, although the recirculation of the solute represents a reduction in energy expenditure, then more complex of operating expenses must be represente.

In the title of Figure 2 there is no mention of the color green and in the text there is no mention of the color black, in fact, the color black does not appear in the diagram. Please, improve the presentation of your graph or otherwise restructure it to a Sankey diagram, for a better representation of the exergetic analysis.

In Figure 3, it is not clear where the colors yellow, gray, and orange appear. Please, find a way to highlight them with an element or choose another graphic method where the section they occupy is clear.

Lines 301 and 302 “For the FO membrane unit, selecting membranes with high water permeability and low pressure drop can help minimize physical exergy destruction;” add the reference to confirm this affirmation.

Lines 305 and 307 “Previous studies have also shown that connecting FO membrane units in series can reduce chemical exergy destruction by stabilizing concentration gradients across the membrane [46].” Please, add diagram with information mentioned in lines 301 and 302 and do a global proposal for improvement, mentioning the possible repercussions of these modifications, supported with more bibliography.

Comments for author File: Comments.pdf

Author Response

Response to reviewer 2 is attached.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The current study analyses two FO desalination configurations: single-pass and regenerative configurations. The later showed higher SEC (kWh/mw) and lower water recovery. The thermodynamic evaluation is comprehensive, especially, the energy exergy analysis (i.e., this is a key point for actual implementation of the technology), which provides a good insight on future FO development. The main comment to be addressed is the comparison of the current results to those found in the literature. FO has been extensively researched, however, only few results in the current study is compared to previous investigations. Below some points to be addressed.

• Introduction Section: the state-of-the-art in FO exergy analysis is nor well covered. The reviewer suggests expanding on this topic.
• The study lacks (in some sections) proper comparison with other studies in the literature. For instance: a) how do the calculated SEC compares to lab scale and pilot scale studies in the literature, b) same for water recovery rates
• Can the authors add a table showing energy consumption of individual components of FO and compared to others in the literature.
• The conclusions section is a mere repetition of the findings, the authors might want to consider adding future implications

Author Response

Response to reviewer 3 is attached.

Author Response File: Author Response.pdf