Solar-Powered Direct Contact Membrane Distillation System: Performance and Water Cost Evaluation

Round 1

Reviewer 1 Report

It would be worth answering the question:

Should the analyzes presented in the paper be considered universal in research on the acquisition of fresh water? Especially:

1: Based on the procedures contained in the paper and in the cited literature, can the reader carry out similar analyzes for his country?

2: According to the authors, are countries with a national income per capita lower than Pakistan able to obtain fresh water according to the given procedures?

3: Can the paper serve as a preliminary study on the extraction of fresh water towards creating conditions for low-income countries?

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

1. Fig 4 is not visible

2. The authors justified the cost of a solar-driven DCMC system. From a cost-effectiveness perspective, what is its advantage over other systems (in terms of cost/L?

3. Is there any rejection data?

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

In this paper, this author provided detailed evaluation on solar-powered DCMD system in Pakistan, and this methodology that used in this paper would be beneficial for DCMD design and solve the critical fresh water challenge. The author also did a great job in provide a systematic review on membrane desalination (especially from membrane distillation approach). 

1. line 52-54: the author mentioned that thermally driven desalination has higher energy consumption than membrane based desalination, could the author add reference on this statement? 
2. line 127-127: based on the content, it seems “low temperature operation” is one of the approach that could help such the high energy consumption, it that correct? If so, could the author clarify in the content? Current wording may cause confusions to some audience that low temperature operation has already been applied, then it might lead to the impression that high energy consumption is no longer an issue
3. In section 1, the author provides a very detailed review on the previous study of solar assisted MD. This is very helpful for the general audience to understand the current status of this area, however, it might “dilute” the overall content of a research paper. Would the author consider to short this part? For example, maybe the previous study can be summarized into a literature review table
4. Figure 4 is not showing properly in the manuscript. Could the author fix that?
5. Section 2 and 3 actually have close connection: section 3 described the current freshwater status in Pakistan, and the criticalness of MD. section 2 described the potential of development a solar-assistant MD in Pakistan. Thus, would the author may consider to combine this 2 section?
6. In figure 7, would it be more accurate to call “Tubular solar thermal collector” instead of “tubular SWH”
7. In section 4, for the DCMD system, to have a sufficient dissolution,  is there any requirement on the “driving force” between hot seawater and permeate water (like temperature difference, or molar flow rate ratio)?
8. Equation 7 font format seems different as the others, could the author fix that?
9. Section 6 used the concept of “solar fraction”, could the author provide a definition when it first showed?
10. Figure 11, is T delivered means seawater temperature? If so, could the author use consistent terms in the content and the figure? This could help to avoid confusions when audience read the manuscript
11. Figure 12, the axis title and scale bar is quite small and a little hard to read, could the author change the font size?
12. In DCMD system simulation, could the author provide data or discussions on the model validation? The accuracy of the model would be critical on using this model to guide the future design
13. For the capital cost, what’s the life-cycle (years) that the cost is based on? For instance, membranes could be fouled during operation, and need to changed. 
14. Could provide some discussions on how to use this model to help the DCMD design in actual engineering work? 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

Comments

1. The literature review should become more comprehensive.

2. Fig. 1: Does the authors mean solar still instead of solar distillation in the last box of thermal driven distillation?

3. The quality of Fig. 1, Fig. 2 and Fig. 18 should be improved.

4. Line 167: kg/m² is correct.

5. Line 173: What is the currency of production cost? USD?

6. The referencing standard of Fig. 3 is different from the main text.

7. Fig. 4 cannot be seen in pdf file.

8. Section 3 should be inserted in the section 1 of the paper. Because it is related to this part.

9. The referencing standard of Fig. 4 is different from the main text.

10. Line 370: m³ is correct.

11. The references of the equations should be mentioned in the manuscript.

12. Line 487: What is the Greek item?

13. Line 495-496: Different standard of referencing.

14. Line 498: 5. Results and discussion is correct.

15. Line 566: The unit of the storage tank is USD/m²?

16. Line 566 and line 627: There is no need to mention (2017) in the text. The same problem in the lines 720-722.

Author Response

We did not received any comments from Reviewer 4.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

The paper is acceptable in the present form.