Techno-Economic Assessment of Air and Water Gap Membrane Distillation for Seawater Desalination under Different Heat Source Scenarios
Round 1
Reviewer 1 Report
I trust the following comments help the authors
(1) Introduction
The introduction is incomplete in that no review of existing economic evaluation of MD technology was provided. Therefore, the research gap was not identified and no compelling argument was provided for this study.
No hypothesis provided to test
No research questions to support hypothesis
No justification of methodology
(2) Materials and Methods
Taking data from a small flat sheet MD unit in a lab to full scale is fraught with danger. I have severe reservations about this approach.
You surely need to have a process flow diagram, equipment list, stream tables and a PnID before you can actually cost an MD system? Please complete these items.
The use of the SCOW method is not justified, why not look at stochastic analysis of the economics?
(3) Results and Discussion
As the whole approach of this study is highly flawed how do we know that the predicted economic values are realistic? surely you need to have a pilot plant MD system to verify that you do not have a case of "rubbish in, rubbish out"
Author Response
Having carefully read the contributions and suggestions offered by the editor and reviewers, the authors would like to thank them for their revisions and to explain their comments. Some of the uncertainties expressed might not have been fully explained in the original document. For this reason, new explanatory comments have been introduced in the manuscript that will definitively clarify the doubts expressed. In this sense, the introduction, materials and methods and results sections have been modified and new references have also been included to confirm our methodology, experimental results and discussions.
Reviewer 1
I trust the following comments help the authors
The authors appreciate your comments.
(1) Introduction
· The introduction is incomplete in that no review of existing economic evaluation of MD technology was provided. Therefore, the research gap was not identified and no compelling argument was provided for this study. No hypothesis provided to test. No research questions to support hypothesis. No justification of methodology.
The authors would like to thank the reviewer for this suggestion. The introduction has been improved by adding more detailed information in lines 67-77; 82-91; 98-101; 107-117, as well as table 1. The hypothesis of this paper was not sufficiently clear in the old document. For this reason, the hypothesis and some research questions are now clarified in lines 119-132. The authors consider that the methodology used and the objective of the work are properly justified with the comments and references included in lines 147-152 and 173-180.
(2) Materials and Methods
· Taking data from a small flat sheet MD unit in a lab to full scale is fraught with danger. I have severe reservations about this approach. You surely need to have a process flow diagram, equipment list, stream tables and a PnID before you can actually cost an MD system? Please complete these items. The use of the SCOW method is not justified, why not look at stochastic analysis of the economics?
The authors would like to thank the reviewer for the close analysis of the methodology proposed in this paper. Of course, as suggested by the reviewer, different elements (flow charts, equipment lists...) have been used in this work for the calculation of the different costs, which although they are not explicitly included in the document, their use is implicit in the development of the methodology section.
On the other hand, the authors wish to point out that there are many methods for the techno-economic analysis of a process. Each method has its advantages and limitations. In this sense, the authors have considered the use of the SCOW method, as this or its modifications is the most used method in desalination processes. For the purpose and limitations of this work (lines 147-152; 342-346) the authors consider that the method used is now well justified in lines 173-180 and it is supported by a large number of studies, which have been added to the literature of this manuscript.
(3) Results and Discussion
· As the whole approach of this study is highly flawed how do we know that the predicted economic values are realistic? surely you need to have a pilot plant MD system to verify that you do not have a case of "rubbish in, rubbish out"
As with the previous comment, the authors would like to highlight that the results obtained in this work are an estimation, an approach, with the purpose of providing an order of magnitude, which compares different configurations little studied and four different scenarios with the same method. Of course, it is not possible to assert that the data are 100% accurate, as it is not a work focused on the investment of a true project. Nevertheless, the realism of the results is as great as possible, taking into account the limitations of the method used and the starting MD scale. All baseline data have been carefully checked, including estimates and models from the literature. The results obtained are in accordance with other referenced studies as discussed in the paper. At all times, the authors have pointed out the limitations of the method, as well as the lack of large-scale MD studies. All of this is clearly stated in lines 147-152; 342-346; 348-357, tables 1 and 6 and in the introduction and conclusions sections.
Reviewer 2 Report
Major Revision
The author has demonstrated the feasibility of techno-economic assessment of AGMD and WGMD for seawater desalination. This is a good topic that may arise some researcher's interests studying economic feasibility of MD. However, in this research paper, there are some flaws that have been mentioned below. The author must modify the manuscript for better understanding attract large number of audiences.
The introduction section seems to be very generalized. Kindly provide some more information based on the previous study. As far as economic assessment of MD is concerned, this research work is not the first one and even, a lot of research works were already performed, thus the state-of-art must be discussed in order to highlight the importance of this research article. The author should have added the previous research outputs (with conditions) by comparing the present one in order to show the viability of the present research work. A detailed schematic diagram of AGMD and WGMD is highly recommended as it is missing from this present manuscript. Typically, heat exchangers and storage tanks are the two major cost drivers of the capital cost. Therefore, evaluation of these cost drivers is necessary. The author must come up with scientific discussions. Kindly cite few articles from “Membranes”, “Polymers” and “Water” journals (MDPI)
Author Response
Having carefully read the contributions and suggestions offered by the editor and reviewers, the authors would like to thank them for their revisions and to explain their comments. Some of the uncertainties expressed might not have been fully explained in the original document. For this reason, new explanatory comments have been introduced in the manuscript that will definitively clarify the doubts expressed. In this sense, the introduction, materials and methods and results sections have been modified and new references have also been included to confirm our methodology, experimental results and discussions.
Reviewer 2
The author has demonstrated the feasibility of techno-economic assessment of AGMD and WGMD for seawater desalination. This is a good topic that may arise some researcher's interests studying economic feasibility of MD. However, in this research paper, there are some flaws that have been mentioned below. The author must modify the manuscript for better understanding attract large number of audiences.
The authors appreciate your comments.
· The introduction section seems to be very generalized. Kindly provide some more information based on the previous study. As far as economic assessment of MD is concerned, this research work is not the first one and even, a lot of research works were already performed, thus the state-of-art must be discussed in order to highlight the importance of this research article. The author should have added the previous research outputs (with conditions) by comparing the present one in order to show the viability of the present research work.
The authors would like to thank the reviewer for this suggestion, which has been taken in account. The introduction has been improved by adding more detailed information and a state of the art in lines 67-77; 82-91; 98-101; 107-117; 119-132 as well as Table 1.
· A detailed schematic diagram of AGMD and WGMD is highly recommended as it is missing from this present manuscript.
A detailed diagram of the AGMD and WGMD configurations, as well as the pilot plant used have been included in Figures 1 and 2, respectively.
· Typically, heat exchangers and storage tanks are the two major cost drivers of the capital cost. Therefore, evaluation of these cost drivers is necessary.
Effectively, heat exchangers and storage tanks could become one of the major capital costs for MD. However, throughout the document (lines 109-112) it is commented that one of the factors that may affect the techno-economic analysis is the type of module used, among other factors. In this sense, the module used in this study is flat, predominantly in MD, which has a low volume area ratio, requiring a lot of material. For this reason, the costs related to the membrane module are considerable. Nonetheless, the evaluation of the costs for the heat exchangers has been taken into account, as shown in lines 233-240. Finally, in this study a continuous feed and cooling flow was assumed, avoiding the use of storage tanks, a fact that was not sufficiently explained in the document. A further explanation has been added to lines 159-162 and 230-231.
· The author must come up with scientific discussions. Kindly cite few articles from “Membranes”, “Polymers” and “Water” journals (MDPI).
Taking into account the reviewer's suggestion, some comments have been included in the results and discussion section (lines 272-273; 277-278; 284-290; 298-304; 324-328; 379-381 and table 6 has been improved). On the other hand, a greater number of current articles have been included, in line with the subject matter of the present study.
Round 2
Reviewer 1 Report
The manuscript is much improved and I recommend publication
Reviewer 2 Report
After thorough evaluation, the manuscript seems to be well revised. The revised manuscript can be accepted in the present format.
