Review Reports - Feasibility Study of a Reverse Osmosis Desalination Unit Powered by Photovoltaic Panels for a Sustainable Water Supply in Algeria

Round 1

Reviewer 1 Report (Previous Reviewer 4)

P2-L86 ："The energy requirements for BWRO and SWRO are approximately 1-1.585 kWh/m³ and 3-4 kWh/m³, respectively "need to add punctuation at the end of the sentence.

P6-L261:The text format in Table 1 should be uniform.

P7-L324:The title of Table 3 should be at the top of the table, and Table 3 should be centered in the article.

P8-L326-328:Words crossed out with lines should be deleted from the text.

P9-L373-394：The blank part of the article should be deleted.Other similar problems in the text also need to be modified.

P14-L514:The space after the sentence "Every four panels are" should be removed.

P20-L627:Table 7 should be centered in the text.

Moderate editing of English language required

Author Response

Please see attachment

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

some minor comments

improve the abstract, especially at the end with the observation of " 32%–80% recovery" then it just ends. So a better concluding sentence.

Also there is not that much discussion on recovery rate in the actually manuscript so a better lead up to it as well as comparing with other systems, there is mention that 10% is the minimum at the beginning of the paper. Can you comment on why the range is so broad and how that impacts the system?

introduction is too long and takes away from the paper, would recommend to shorten it since the R&D section should be the main focus

Avoid figs to have both red and green (make more colorblind safe)

How does it compare to other similar systems/ecosystems? maybe some additional commentary at the end on that since there is a lot of data what are the alternatives? cost analysis for implementation?

Can improve the phrasing, some of the manuscripts reads more so like a wikipedia article rather than an academic journal, try to use words such as "improved" "Observed" "similar" instead of for example "the filter only lets water molecules through" something like "the filter allows only water molecules". This will help increase the quality of the paper. But the overall English is good and understandable.

also avoid repetitions such as "We found the recovery rate for system operation was determined to be 32%" you can say We found the recovery rate for system operation to be 32%" removing the repetition

Author Response

Please see attachment

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

This research seeks to improve our understanding of potential sustainable and cost-effective solutions to water scarcity in arid regions, or areas with increasing pressures on water supply due to emergency, drought, or saltwater intrusion. This specific work looked to evaluate the RO membrane performance and energy consumption under the influence of different conditions of applied pressure, salt concentration and temperature. This is not particularly novel, but could inform future development or rollout of small water treatment solutions in water stressed areas.

In reading through the submission some general comments:

· The article is imbalanced and lacks a clear objective. This is a relatively simple research project but allocates significant portions of the article to providing introductory and background information, with repetition throughout, without making clear linkages to why this specific research project conducted here is novel and necessary to advance the science.

· The structure of the article could be improved. The introduction needs to be shortened, the methods and materials section needs to be more focused, and the novelty of the findings and results need to be made clear.

· There are problems with the citations, with incorrect numbering throughout.

· There are many specific comments, however I have only provided some here as examples as I feel this paper needs a complete overhaul. A re-write should not be limited to these comments only:

Introduction

P2. Line 54-55... sentence starting “With the development of humans… where he now lives…” is poorly translated and needs revision

Line 61. “Indeed, the WHO considers that there is water stress when a human being has less than 1700 m3 of water per year and a shortage when he has less than 1,000 m3 per year” – This statement should include a reference to the WHO recommendation and it should be revised to make it clear that this is a definition of regional per capita water stress – for all water needs in a community. As written in implies an individual requires this quantity for personal use. As we know, even in “water rich” areas, personal use is in the region of 180-200 litres per day for consumption, cooking, washing, flushing toilets. Much of the water consumed by society is for non-personal use including agriculture, industry, healthcare, commercial services, etc. This needs to be made clearer that there are societal needs and personal needs for water.

Citation [1] used on line 64, and line 71 is incorrectly attributed – e.g., this reference is from 2003 but refers to how things were in 2015 (wrong reference used)

Citation [2] is incorrectly attributed on line 65 - out of date, and does not include an estimate to 2050 as stated – a more recent reference should be used (last accessed in 2008 suggests the authors have not referred to most recent literature sources). Also the author in the hyperlinked reports is not “Sandia”

Line 68 – first use of MENA should include definition of the acronym

P 3

Line 104 – this statement does not make sense “By 2030, groundwater resources in the MENA region will be decreasing over time and the water demand is expected to exceed 13 million m3. Therefore, the desalination capacity is expected to increase speedily by around 110 million m3/d”… if demand is only 13 million – how can daily capacity require to be 110 million - please review the wording/units etc.

Referencing numbers are all incorrect; e.g., Line 126 – reference to AM Helal [29] but this is [28] in the reference list. Line 131 reference to Bilal [31] is listed as [30] in reference list etc. etc. ...too many to list all the errors

Line 157 specific energy consumption … add brackets around (SEC)

Line 159 brackish water reverse osmosis … add brackets around (BWRO)

Line 168 They discuss … remove the word “detail”

Line 197 … rate of 100 liters of water per day … per person?

L189 “Additionally, the plants require regular maintenance and repairs, which can be costly...” and P4 line207-208 . The biggest constraints of the desalination system are its energy consumption per cubic meter product and environmental impacts due to discharges of brine in the natural environment”… these issues are not later discussed in terms of the findings of this research… There was no economic evaluation of the proposed small-scale system, no comment on whether the system provides a reduction in the maintenance/repairs/operational demands.

L216 “water supply is 4.4 million m3/d. The plants currently provide 2,12 million m3/d” 4.4 uses decimal where as 2,12 uses comma separation… prefer to use decimal consistently.

Overall, the Introduction is long and concludes towards the end of p5 with a description of the current research. Some effort could be made to make the introduction shorter and more concise. Some of the literature review could perhaps be summed up as a table. At the end of the Introduction section the authors could lay out more clearly why the current research is needed and is novel. The novelty and contribution to current knowledge is not stated clearly enough. The authors should lay out the use-case for the small scale system they are testing. Is this intended for small community/household/facility scale, or is it intended to pilot a small version of a scalable model that could be used at a larger scale. If the latter, also need to state how this small pilot is a good representation of a scalable model.

Line 326-328 stricken out – should remove text that is not needed.

Line 338 “Skid” should not be capitalized

Line 342 8KW/d should be stated in conventional power consumption units kWh instead

Line 344…. “some form of activated carbon”…. State specifically what type of AC filter was used.

Line 355 “… high-pressure pump HP..” should read “HP pump”

Table 4 – it is unnecessary for all physicochemical parameters to be stated to three decimal places, and unlikely that the instrumentation used to analyze each can provide such precision. The instrumentation used to conduct these measurements and sensitivity/accuracy are not stated. The materials and methods section should be used to present the approaches/equipment/techniques used to take measurements, not the results variously presented from Pages 9-11

Methods and Materials

The methods and materials section needs reorganized and some sections removed or placed elsewhere. This applies not just to analytical test results but also to section such as on P. 10 starting at line 421 – this is background information which if the authors find necessary to discuss should either be placed in the introduction (to justify the research) or the discussion (to contribute to interpretation of results and application of the study findings). It is not appropriate in the Methods and Materials section.

Results and Discussion

This section is missing some key information that could be used to improve the novelty of the findings, such as economic evaluation, or discussion on ease of operations and maintenance, lifespan of the system – to demonstrate feasibility. This section, and the conclusion do not match the narrative set out in the Intro/Methods section as to some of the key challenges presented earlier in the article.

Overall the English Language is ok, however the article could benefit from the skills of a professional English-speaking copy editor to improve several minor errors with English, punctuation, numerical presentations etc. throughout.

Author Response

Please see attachment

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The English throughout the MS, could do with some attention. In the introduction you should make the text more concise and focused. You should remember that you are not dealing with a new technology. Rather the technology is proven. Therefore you can take it as read that your reader will know what reverse osmosis is or multi stage flash is. Every point you make (unless its your own) should have reference support. This is not currently the case. In my view the introduction should be refocussed to deal solely with Algeria, and should clearly quantify the magnitude of the problem you are trying to address, why the problem is challenging, and why the approach you have selected to investigate may provide a partial solution.

1. Abstract define RO, NF, and PV at the first point of mention

2. Line 54, change "Water" to "Fresh water", as most of the planets surface is covered in saline water. I dont think that lines 54 - 74 are required, please delete

3. Line 75- please note that around 107.95 million m3/d of installed desalination capacity was present globally at the end of 2022 - source waterintel.

4. Line 76 -You need a source reference from 2022/23 for the 10% growth claim. Contracted global capacity (constructed, + under construction, + approved but not built) is around 321 million m3/d, of which only 5.1 million m3/d were signed as new contracts during 2022. I think if you want to make this point it would be useful to spend a bit of time putting together a graph showing installed production as a function of time covering 2022 - 2050 including constructed, under construction and contracted plants. - This would increase the impact of your paper when published by broadening its readership.

Line 81 - 86. It would be useful to define the magnitude of the problem in Algeria quantitatively. For Algeria has a population of around 44 million. If each person requires 100 L/d (the minimum requirement in many western countries, in practice most consumers use between 100 and 200 L/d, when the water is not metered) then the required water supply is 4.4 million m3/d. Algeria currently provides x million m3/d. The required shortfall is z million m3/d -- This allows the magnitude of the problem you are trying to address to be easily seen by the reader

Introduction to Line 271 - In my view the introduction is not concise or focussed. Please rewrite, by identifying the size of the problem, its potential solutions and how you intend to address them. The use of PV with RO is not new and I would have expected the introduction to review what has been done and indicate which approach you are following or how you are improving on the past work, e.g.

Shalaby, S.M., Sharshir, S.W., Kabeel, A.E., Kandeal, A.W., Abosheiasha, H.F., Abdelgaied, M., Hamed, M.H. and Yang, N., 2022. Reverse osmosis desalination systems powered by solar energy: Preheating techniques and brine disposal challenges–A detailed review. Energy Conversion and Management, 251, p.114971.

Maftouh, A., El Fatni, O., Bouzekri, S., Rajabi, F., Sillanpää, M. and Butt, M.H., 2022. Economic feasibility of solar-powered reverse osmosis water desalination: a comparative systemic review. Environmental Science and Pollution Research, pp.1-14.

Ghafoor, A., Ahmed, T., Munir, A., Arslan, C. and Ahmad, S.A., 2020. Techno-economic feasibility of solar based desalination through reverse osmosis. Desalination, 485, p.114464.

Monjezi, Alireza Abbassi, et al. "Development of an off-grid solar energy powered reverse osmosis desalination system for continuous production of freshwater with integrated photovoltaic thermal (PVT) cooling." Desalination 495 (2020): 114679.

This list is not exclusive and Google Scholar records several thousand papers that may relevant, but these papers will introduce you to the historic literature on this subject

Line 175 - This is not correct, the known fossil fuel resources (coal, shale, oil, gas, hydrate) could last for 1 - 2 centuries at current exploitation rates. However the Western global national governments have taken a collective decision to phase out fossil fuels by 2050/70 as part of the UN Net Zero agenda, and are attempting to push this Net Zero agenda on the rest of the world. You should note that the typical government mantra since the 1950's has been that the world will run out of fossil fuels within about 20 years of the stated date. Instead oil production has risen 10 fold since the 1950s and coal production is currently a record global levels. - rephrase if you want to use this statement, otherwise omit

Figure 1 - make sure that you have copyright permissions to use this figure - otherwise redraft and add things to it to create a new drawing.

Line 182 - not sure that this correct my own solar panels contain a large part which is made from fossil carbon, and wires/glass which is made from mined operations. I think you mean non polluting once in operation - please clarify.

Line 225 - please clarify the abbreviation

Line 236 - Please state the manufacturer and suppliers of each of the items shown in Figure 2 and Table 1. I note that you used 12 PV cells, placed on a vertical structure. You should give the full technical specifications for the panels used, the angle of fixing and orientation. You should indicate the controllers used, and the expected performance of an individual panel as a function of time, e.g. from 6 am to 6 pm. Not all PV's have the same performance profiles. Monocrystalline - black; polycrystalline - black, and polycrystalline - white all have different performance characteristics and these characteristics vary with manufacturer. Different controllers also have different performance characteristics.

Figure 4 - please define each element of Figure 4, clearly identifying all the equipment used. I presume the battery was a Li in 4 - 8 kW range if you had 3 kW of solar panels. The invertor used should be stated. Was it a hybrid invertor? This information is required to allow another to reproduce your work.

Line 304 - you have two fig 4 - please check figure numbers

Line 335 - Figure 5 you need a time scale on the x axis. All abbreviations in the figure need to be specified in the caption

Line 339 on line 283 you state the voltage was 400 V. How does this relate to the stated 240 V on line 339?

Line 361 - You need to state what water you are using, and its composition, in sufficient detail to allow another to duplicate your work. It is not clear whether you charged your batteries at your facility and them took them with the RO unit to Bou-Ismail town to process water of different salinities. Please clarify.

Methodology - The description provided is incomplete. The reader needs to be able to reproduce exactly what you have done from your description. This is not possible from your text.

In the results section you use the words "we" and "our". Please rephrase all these sentences to omit these two words.

Table 3 please replace all "," with "." otherwise your average reader will think the values are 1000 times greater than those you intend.

In the methodology section you should list all the instruments, and their calibration/measurement procedure, used to give the results in Table 3. Table 3 should be transferred from the results section to the methods and materials section as per MDPI instructions to authors

Figure 14 - the analytic measurement instruments and their calibration for each of the measurements in this figure should have been detailed in the methods section. The same is true for the results in Table 4

I have gone through your MS. I think that the English needs some attention throughout. However my main problem with the MS, is that your methodology is poorly defined, to such an extent that it is not possible to properly evaluate your results.

What I want to see in the methodology is a detailed description of what was done listing all equipment used (manufacturer and specification), all analytical equipment used, all calibrations used, all water sample locations identified, all sites for the water treatment clearly identified. The water volumes used to obtain each data point, the water flow rates used, etc. I need to be able to reproduce your work exactly from your description.

You need to add a section before the conclusions placing your work in its scientific context and showing how you have moved the science forward.

I can see nothing in this MS as written which would justify its inclusion in a high impact journal, such as Sustainability. In my view the MS needs to be substantially technically improved to justify inclusion in Sustainability. As it stands it has no new technical information. The use of solar PV to desalinate water is several decades old. This literature of >8000 papers (see Google scholar) is not reviewed in the MS. There are more than 800 patents which address this issue, none of which have been referenced in the MS (see google patents or free patents on line or appropriate government websites).

The article if published in Sustainability needs to have a reasonable chance of getting 4 or more citations within 3 years of publication. I cannot see that happening with the MS as currently written. To have a chance of doing that you need to

1. Improve the technical review in the Introduction demonstrating what you are doing in this study to move the science forward

2. Improve the methodology and experiment description as noted above

3. Add a section show how your results move the science forward and will if adopted widely in Algeria or neighbouring countries provide an economic solution which could be applied to villages. You should indicate the current water delivery price in the towns/cities in Algeria $/m3 and indicate what the costs are for your set up, and what the cost expectancy will be if your process is used in the remote villages.

These changes could add 5 to 15 pages to your MS length during the revision.

Author Response

Question 1: The English throughout the MS, could do with some attention. In the introduction you should make the text more concise and focused. Abstract define RO, NF, and PV at the first point of mention

Response 1:

-We make a change (page 1, Abstract) as follow:nanofiltration (NF) (line 25) and reverse osmosis (RO (line 26)), photovoltaic (PV) line (39).

-The English of the MS is improved with some attention.

-The introduction is more reworked and modified .

Question 2: Line 54, change "Water" to "Fresh water", as most of the planets surface is covered in saline water. I dont think that lines 54 - 74 are required, please delete

Response 2:

-"Water" is changed to "Fresh water" line (54)

-The following sentence is deleted from introduction:“Unfortunately, it is not available in infinite quantities on our planet and it is not always available where it is needed most”

Question 3: Line 75- please note that around 107.95 million m3/d of installed desalination capacity was present globally at the end of 2022 - source waterintel.

Response 3:

We have added the following sentence:

Around 107.95 million m3/d of installed desalination capacity was present globally at the end of 2022 and the market continues to grow [2] (line 76).

Question 5: Line 81 - 86. It would be useful to define the magnitude of the problem in Algeria quantitatively.

Response 5:

-We added the following paragraph to define the magnitude of the problem in Algeria quantitatively:

Algeria has a population of around 44 million. If each person requires 100 L/d (the minimum requirement in many western countries, in practice most consumers use between 100 and 200 L/d, when the water is not metered) then the required water supply is 4.4 million m³/d. The plants currently provide 2,12 million m³/d equivalent to 780 million cubic meters of water per year, which is not enough to meet the needs of over 10 million people. The required shortfall is 2.28 million m³/d.

Algeria is currently building several desalination plants to meet the growing demand by reaching a capacity of about 45% of fresh water. Two seawater desalination plants SWDP are under construction with a total capacity of 600000 m³/d and 80,000 m³/d. In addition, at present, five plants SWDP are under construction with a capacity of 300000 m³/d for each of them. Others approved but not built, by 2024 there is a program to complete six SWDPs for a capacity of 300000 m³/d for each of them. For sustainable desalination, renewable energies could be a good solution, especially since Algeria is one of the sunniest countries in the world, thus favoring the production of solar energy without neglecting the important wind and geothermal deposits located essentially in the south of the country. Despite the desalination plants being located in the north all along the coast, they can obviously be powered by renewable energies produced in the south and injected into the national grid.

Question 6: Introduction to Line 271 - In my view the introduction is not concise or focussed. Please rewrite, by identifying the size of the problem, its potential solutions and how you intend to address them. This list is not exclusive and Google Scholar records several thousand papers that may relevant, but these papers will introduce you to the historic literature on this subject

Response 6:

-The introduction is rewritten, identifying the size of the problem.

-Many paragraphs are added in MS , new papers are introduced in the introduction:

For the performance evaluation of the desalination system, A.M. Helal [21] 2008 conducted an economic feasibility analysis of alternative designs of a PV-RO desalination unit for remote areas in the United Arab Emirates. He used three different energy systems a diesel generator, PV-diesel, and an off-grid PV system without battery backup to operate the RO system. It was shown that the permeate productivity of 20 m³/d was produced using the assisted PV-RO-diesel but the freshwater of 44 m³/d was obtained using the solar RO on a clear and sunny day. In fact, because desalination is an energy-intensive process, a sustainable energy source is needed [22]. H. Bilal et al [23] 2016 carried out a study for portable photovoltaic reverse osmosis (PVRO) system with a battery and without a battery to run the RO system for 5 hours. Without energy storage, the analysis showed that permeate productivity was 3.8 L/h, while it increased to 5.9 L/h with the battery. The freshwater productivity was 9.8%. In addition, they found that the battery-less PV system was more economically suitable than the battery-powered system. Using HOMER and Excel software, a techno-economic study of an off-grid PV-RO system in 9 districts of Iran was conducted by A.Mostafaeipour et al [24] 2019. The study concludes that solar desalination is an economically viable technology. Ghafoor, A et al [25] 2024 performed an experimental study of an RO plant (500 L/h) coupled with a solar photovoltaic PV system (2 kWp ) to analyse the techno-economic feasibility. The performance of the PV-RO system in terms of power produced, and membrane productivity with its economic analysis was evaluated. They found that 15-20% of the PV energy is increased by tracking the PV system, while 5-10% is due to cooling the PV panels. The cost per liter of desalinated water was calculated to be PKR 0.72 with a total monthly profit of PKR 54000. The payback period of the PV-RO system was calculated to be 1.83 years. Shalaby, S.M et al [26] 2022 focused on solar-based reverse osmosis plants, which have been established to decrease the specific energy consumption by using photovoltaic or solar thermal power plants; in particular, the organic Rankine cycle. In addition, various preheating techniques performed by recovered heat from other systems, such as photovoltaic cooling unit, humidification-dehumidification process, and hybrid systems used for brine disposal challenges were presented and discussed. Maftouh et al [27] 2023 presented a comparative and systematic review of the economic feasibility of using solar photovoltaic reverse osmosis for desalination in the MENA region. They highlighted the importance of RO technology powered by renewable energy resources, in which the detailed challenges associated with the solar RO technique were elucidated. They concluded that RO systems are more cost-effective in MENA countries where water salinity is lower, which explains why North African countries use RO systems. On the other hand, the Gulf Cooperation Council countries choose thermal processes because of the higher salinity of the water. It is found that the use of renewable energy in desalination is economically feasible depending on the specific needs and water conditions of each country. To maximize the rate of freshwater production, Monjezi, Alireza Abbassi, et al. [28] 2020 developed an off-grid solar energy-powered reverse osmosis desalination system with integrated photovoltaic thermal (PVT) cooling. They evaluated and compared the required solar panel area with and without a cooling system. The results showed that a reduction of 0.12 kWh/ m³ in the specific energy consumption SEC of the RO unit can be achieved by using PVT cooling, resulting in a 6% reduction in solar panel surface.

Algeria is facing a severe water crisis due to the increasing demand for water, limited water resources, and climate change. This last has led to decreased rainfall and increased temperatures, resulting in increased water evaporation. In addition, the lack of water has caused severe damage to the environment, leading to desertification and soil erosion. This has had a negative impact on the country's agricultural sector, this leads to reduced crop yields and increased food insecurity. In order to address the water crisis in Algeria, the Algerian government has taken measures to increase the water supply, improve water management and reduce water wastage. Desalination is seen as a viable solution to this problem, as it would provide a reliable source of freshwater that can be used for drinking, agriculture, and industry.

Desalination is an alternative option to Algeria's water crisis. The cost of desalination is a major challenge. In fact, the plants are expensive to construct and operate, and consequently, the water produced is often too high. In addition, the process of desalination is energy-intensive and expensive. The plants require a large amount of energy to operate, which can be difficult to obtain in some Algerian regions. Additionally, the plants require regular maintenance and repairs, which can be costly. The plants use reverse osmosis technology, which is the most efficient and cost-effective method of desalination.

-The following refences are added in the manuscript:

[14] El-Ghzizel S, Tahaikt M, Dhiba D, Elmidaouia A, Taky M (2021) Desalination and Water Treatment www. deswater. com. Desalination Water Treat 231:1–15.

[15] Enas Taha Sayed , A.G. Olabi , Khaled Elsaid , Muaz Al Radi , Rashid Alqadi , Mohammad Ali Abdelkareem. Recent progress in renewable energy based-desalination in the Middle East and North Africa MENA region.Journal of Advanced Research. 2022 Sep 13;S2090-1232(22)00197-7. https://doi.org/10.1016/j.jare.2022.08.016.

[16] Salah Basem Ajjur, Sami G. Al-Ghamdi.Towards sustainable energy, water and food security in Qatar under climate change and anthropogenic stresses.EnergyReportsVolume 8, Supplement 3, June 2022, Pages 514-518 .

[17] H.A. Shawky, A.A.A. Fatah, M.M.S.A. Elfadl, H.M. El-Aassar, H.A. Shawky, A.A.A. Fatah, M.M.S.A. Elfadl, Design of a small mobile PV driven RO water desalination plant to be deployed at the northwest coast of Egypt, Desalin. Water Treat. 55 (13) (2015) 3755–3766.

[18] Dirk Herold, Apostolos Neskakis. A small PV-driven reverse osmosis desalination plant on the island of Gran Canaria. Desalination 137 (2001) 285-292. https://doi.org/10.1016/S0011-9164(01)00230-2.

[19] Junjie Shen, Godfrey Mkongo, Gudrun Abbt-Braune, Silvia. Ceppi , Bryce S. Richards, Andrea I. Schäfer .Renewable energy powered membrane technology: Fluoride removal in a rural community in northern Tanzania. Separation and Purification Technology. Volume 149, 27 July 2015, Pages 349. https://doi.org/10.1016/j.seppur.2015.05.027.

[20] S. Li, A.I. Schafer, B.S. Richards, Renewable energy powered membrane technology:a review of the reliability of photovoltaic-powered membrane system components for brackish water desalination, Appl. Energy 253 (2019) 113524.

[21] A.M. Helal, Economic feasibility of alternative designs of a PV-RO desalination unit for remote areas in the United Arab Emirates, Desalination 221 (1–3) (2008) 1–16.

[22] N. Ghaffour, V.K. Reddy, M. Abu-Arabi, Technology development and application of solar energy in desalination: MEDRC contribution, Renewable Sustainable Energy Rev.,15 (2011) 4410–4415.

[23] H. Bilal, A.H. Alami, M. Farooq, A. Qamar, F.A. Siddiqui, The economic analysis of portable photo-voltaic reverse osmosis (PVRO) system, Technical Journal 21 (2016) 1–6 II.

[24] A. Mostafaeipour, M. Qolipour, M. Rezaei, E.B. Tirkolaeeb, Investigation of off-grid photovoltaic systems for a reverse osmosis desalination system: a case study, Desalination 454 (2019) 91–103.

[25] Ghafoor, A., Ahmed, T., Munir, A., Arslan, C. and Ahmad, S.A., 2020. Techno-economic feasibility of solar based desalination through reverse osmosis. Desalination, 485, p.114464.

[26] Shalaby, S.M., Sharshir, S.W., Kabeel, A.E., Kandeal, A.W., Abosheiasha, H.F., Abdelgaied, M., Hamed, M.H. and Yang, N., 2022. Reverse osmosis desalination systems powered by solar energy: Preheating techniques and brine disposal challenges–A detailed review. Energy Conversion and Management, 251, p.114971.

[27] Maftouh, A., El Fatni, O., Bouzekri, S., Rajabi, F., Sillanpää, M. and Butt, M.H., 2023. Economic feasibility of solar-powered reverse osmosis water desalination: a comparative systemic review. Environmental Science and Pollution Research, pp.1-14. 2023 Jan;30(2):2341-2354. doi: 10.1007/s11356-022-24116-z.

[28] Alireza AbbassiMonjezi, Yingxue Chen, R. Vepa, Abd El-Hady B. Kashyout, Gasser Hassan,Hassan El-BannaFath, Abd El-Wahab Kassem, Mohammad Hasan Shaheed. Development of an off-grid solar energy powered reverse osmosis desalination system for continuous production of freshwater with integrated photovoltaic thermal (PVT) cooling." Desalination 495 (2020): 114679. Desalination.Volume 495, 1 December 2020, 114679. https://doi.org/10.1016/j.desal.2020.114679;

[29] N. Drouiche, N. Ghaffour, M. Naceur, HacèneMahmoudi, Tarik Ouslimane Reasons. for the Fast Growing Seawater Desalination Capacity in Algeria. Water Resources Management. (2011) 25,pp2743-2754.

[30] Hamiche, A. Stambouli, S. Flazi. A review on the water and energy sectors in Algeria: Current forecasts, scenario and sustainability issues. Renewable & Sustainable Energy Reviews. (2015) 41 pp261-276.

[31] Ait MimouneHamiche, A. BoudgheneStambouli, S. Flazi, A. Tahri& H. Koinuma . Desalination in Algeria: Current State and Recommendations for Future Projects. Thermo-Mechanics Applications and Engineering Technology, 2018. ISBN : 978-3-319-70956-7.

[32] Touitou MOHAMMED, Abul Quasem AL-AMIN. Economic and Environmental Studies.Climate change and water resources in Algeria: vulnerability, impact and adaptation strategy . Vol. 18, No 1 (45/2018), 411-429, March 2018;

[33] AitMimouneHamiche, Amine BoudgheneStambouli, Samir Flazi, Allaoui Tayeb. Desalination in Algeria: Photovoltaic Power Plant for TMM (Tahlyat Myah Magtaa) of Oran as a Case Study.Water Resources in Algeria - Part II, 2020, Volume 98. ISBN : 978-3-030-57886-2

[34] NadjibDrouiche, Omar Rodriguez Villarreal, Sara Oualie, Seif El Islam Lebouachera, Richa Soni. Role of desalination technologies in water-energy-food nexus: an opportunity for Algeria. (2022) 1–11. Desalination and Water Treatment. doi: 10.5004/dwt.2022.28538.

[36] YoucefHimri ,Shafiqur Rehman ,Ali Mostafaeipour ,SalihaHimri ,Adel Mellit ,Mustapha Merzouk and NachidaKasbadjiMerzouk. Overview of the Role of Energy Resources in Algeria’s Energy Transition.Energies 2022, 15(13), 4731; https://doi.org/10.3390/en15134731.

[41]David Infield, Leon Freris. Renewable Energy in Power Systems Leon Freris, David Infield John Wiley &Sons, 2019- Technology & Engineering - 347 page. ISBN:1118788583, 9781118788585.

[42]Ministère de l’énergie. Energies Nouvelles, Renouvelables et Maitrise de l’Energie. 2018; Energy.gov.dz. Available online: https://www.energy.gov.dz/?rubrique=energies-nouvelles-Renouvelables-et-maitrise-de-lrenergie#518.

[43] Solar resource maps and GIS data for 200+ countries | Solargis

- The methodology and experiment description are improved

Question 7: Line 175 - This is not correct

Response 7:

-This sentence is deleted :To this end, fossil fuel reserves will only be able to meet energy needs for a few decades to come

-Figure 1 is replotted using website of Solargis

- We rephrased the proposed paragraph as shown below :

At the present rate of exploitation, the known fossil fuel reserves (coal, shale, oil, gas, and hydrates) could last between one and two centuries. However, as part of the United Nations Net Zero (UNNZ) framework, Western national governments have collectively decided to phase out fossil fuels by 2050–2070 and are attempting to impose this Net Zero Program (Agenda) on the rest of the world. It's important to note that governments have consistently proclaimed since the 1950s, that the world will run out of fossil fuels within 20 years of that time. In-stead, since the 1950s, oil production has multiplied tenfold, and coal production is currently at a world record level

Question 7: Line 182 - not sure that this correct my own solar panels contain a large part which is made from fossil carbon, and wires/glass which is made from mined operations. I think you mean non polluting once in operation - please clarify.

Response 7:

The meaning of the sentence is clarified:

-The use of this once non-polluting operation and sustainable energy is an undeniable renovation in terms of the impact on man and the environment

Question 8 :Line 225 - please clarify the abbreviation

Response 8: the abbreviation is clarified

The pilot reverse osmosis installed at Solar Equipment Development Unit (UDES)

Question 9 :Line 236 - Please state the manufacturer and suppliers of each of the items shown in Figure 2 and Table 1. I note that you used 12 PV cells, placed on a vertical structure. You should give the full technical specifications for the panels used, the angle of fixing and orientation. You should indicate the controllers used, and the expected performance of an individual panel as a function of time, e.g. from 6 am to 6 pm. Not all PV's have the same performance profiles. Monocrystalline - black; polycrystalline - black, and polycrystalline - white all have different performance characteristics and these characteristics vary with manufacturer. Different controllers also have different performance characteristics.

Response 9:

-The manufacturer and suppliers of each of the items shown in Figure 2 and Table 1 is added and corrected.

- Full technical specifications for the panels used, the angle of fixing and orientation are given in the section “B. Solar energy potential”

-We added the sentence below:

The characteristics and technical details for the PV panels, as well as the features of the solar inverter, battery, and controller used in the PV system for this study, are displayed in Tables 2 and 3.

-Table 2 is added to the section Materials and methods

Table 2. Characteristics of the PV modules used

Electrical&Mechanicalcharacteristics:
Cell type	Monocrystallinecellwith anti-reflection
Number of cells per module	36 cells (4x9)
Cell sizes	156x156 mm
Module dimensions	1482x674×45 mm
Module weight	12 kg
Panel frame	Anodised aluminium alloy
Type of glass	Tempered glass, 3.2 mm thick
Junction box and connector	IP65, 3 Bypass diodes and compatible cableswith MC4 connector
Operating temperature	40°C à 85°C
Nominal power (W)	150
Open circuit voltage (V)	22.35
Short-circuit current (A)	9.005
Tension mpp (V)	18.54
Curent mpp (I)	8.29

Question 10 :Figure 4 - please define each element of Figure 4, clearly identifying all the equipment used. I presume the battery was a Li in 4-8 kW range if you had 3 kW of solar panels. The invertor used should be stated. Was it a hybrid invertor? This information is required to allow another to reproduce your work.

Response 10:

-All the equipment used in Figure 4 is added: solar PV cell, battery, invertor and controller.

- No, the inverter is not hybrid.

-Table 3 is added to the section Materials and methods as follows:

Table3. Features of the solar inverter, battery and controller in the PV system

Solar battery

Charge controller

Solar Inverter

-Manufacturing technology: AGM-Gel battery.

-Nominal voltage of a battery: 12 V.

-Storage capacity: 250 Ah.

-Nominal voltage of the battery pack: 48 V.

-Autonomy day(s): 2 days.

-Tension nominale : 24/48 V.

-Courant nominal : 50 A.

-Charge controller with MPPT :

-Nominal voltage: 24/48 V.

-Nominal current: 50 A.

-Nominal apparent output power: 5 Va (Victron).

-Nominal input DC voltage: 48 V dc

-Nominal AC output voltage: 230 Vac single-phase.

Question 11: Line 304 : you have two fig 4 - please check figure numbers

Response 11:

The figure number “fig 4” is corrected and all figure numbers are checked.

Question 12: Line 335:Figure 5 you need a time scale on the x axis. All abbreviations in the figure need to be specified in the caption

Response 12:Figure 5 is replotted .

Question 13: Line 339 on line 283 you state the voltage was 400 V. How does this relate to the stated 240 V on line 339?

Response 13:The HP pump Voltage and current is (400v-3.7Amp),We have modified the motor of the pump to run with 240V.

Question 14:Line 361 - You need to state what water you are using, and its composition, in sufficient detail to allow another to duplicate your work. It is not clear whether you charged your batteries at your facility and them took them with the RO unit to Bou-Ismail town to process water of different salinities. Please clarify.

Response 14:

-The raw water used and its composition are shown in detail in Table 5.

- To more clarify, the following sentence is added in section ( 2.2. Solar desalination system):

In the present study,well water of the Bou-Ismail region (salty borehole water) is taken as a benchmark water. Then, different synthetic samples were prepared and analyzed in order to produce saltwater with the same salinity as Mediterranean seawater and Algerian brackish water, Table.5.

Question 15: In the results section you use the words "we" and "our". Please rephrase all these sentences to omit these two words.

Response 15:we rephrased all these sentences in the results section to omit these two words "we" and "our".

Question 16: Table 3 please replace all "," with "." otherwise your average reader will think the values are 1000 times greater than those you intend.In the methodology section you should list all the instruments, and their calibration/measurement procedure, used to give the results in Table 3. Table 3 should be transferred from the results section to the methods and materials section as per MDPI instructions to authors

Response 16:We replaced“all " by " with " and Table 3 is transferred from the results section to the methods and materials section.

Question 17: Figure 14 - the analytic measurement instruments and their calibration for each of the measurements in this figure should have been detailed in the methods section. The same is true for the results in Table 4

Response 17:

-Table 3 is transferred from the results section to the methods and materials section.

-Figure 14 shows the chemical analysis before and after RO membrane filtration is transferred from the results section to materials section.

-The water volumes used to obtain each data point; the water flow rates used are presented in the figures .

Reviewer 2 Report

The application of photovoltaic panels for water desalination using the reverse osmosis process has been investigated on a pilot scale. The article deals with an interesting and practical topic, but in many cases it does not have the necessary features of a scientific article.-T

- - The effects of operating variables on the process has been investigated, but only the results have been presented. The results should be interpreted and the reason for the changes should be fully and accurately explained.

- -It is better to When comparing energy consumption value in case different temperature or pressure (for example Table 7), there will be better to use value of specific energy consumption.

- - It is necessary to give more details of the membrane characteristics

- - The amount of error or accuracy of the data is not specified. The amount of error in the graphs can be shown with error bars.

Author Response

- The effects of operating variables on the process has been investigated, but only the results have been presented. The results should be interpreted and the reason for the changes should be fully and accurately explained.

- The interpretation of the results is made and improved.

- It is better to When comparing energy consumption value in case different temperature or pressure (for example Table 7), there will be better to use value of specific energy consumption.

-The energy consumption valueare plotted and presented in the figures 19 and 20

- It is necessary to give more details of the membrane characteristics

All details of the membrane characteristics are presented in Table 4 (revised paper)

- The amount of error or accuracy of the data is not specified. The amount of error in the graphs can be shown with error bars.

Reviewer 3 Report

This manuscript has serious drawbacks. It cannot be accepted for publication. It is not admisible that in the references list apper links. The scientific studies should be based on previous publications, books or data base. Without a proper literature revision it cannot be evaluated the novelty of this study. I recommend the authors to rewrite the entire paper considering scientific literature.

Author Response

The article has been reworked and we have taken into consideration all the remarks for its improvement, here is the paper in attachment.

Reviewer 4 Report

Title:Feasibility study of a reverse osmosis desalination unit powered by photovoltaic panels for a sustainable water supply in Algeria.

Publish after major revisions noted.

The work in this journal is generally about design of autonomous reverse osmosis desalination system powered by photovoltaic panels in dry environment without water and electricity and the results of its improvement scheme. The factors influencing the conversion efficiency of photovoltaic autonomous reverse osmosis desalination system were analyzed systematically. The results show that the conversion rate and energy consumption largely depend on the pressure, temperature and salinity of the solution. Based on these results, they determined the optimal operation of a reverse osmosis desalination plant powered by photovoltaic panels. This work has great industrial application value.

Some questions are as follows:

P2-L72:The space before the sentence ‘ According to Sandia ’ should be removed. Other similar problems in the text also need to be modified.

P4-L157: In the sentence ‘ It produces an average daily drinking water of 2m3 per day ’ ,for the‘ 2m3 ’ 3 should be superscript. Other similar problems in the text also need to be modified.

P5-L213:There is a blank section above the heading "2.1 Materials and methods", which should be removed.

P6-L232:The explanation of Figure 3 is a not professional enough. It is suggested to label the two pictures a and b in sequence and give a more detailed explanation.

P10-L400:Text after subheading 3.1 should be below Table 3,the current format is crowded. Other similar problems in the text also need to be modified.

P11-L456:Fig.7、8should be properly centered.

P14-L513:Fig.14,The two images shown are not at the same height so they should be lined up and numbered in order. Other similar problems in the text also need to be modified.

P16-L540:The information in Table 5 is stacked with rows causing confusion and needs to be modified.

P21-L661:The format of the references cited in the article should agree with international standard.

Finally, the author should give some examples of other materials used in desalination for electricity generation from new energy sources.

Comments for author File: Comments.pdf

Author Response

P2-L72:The space before the sentence ‘ According to Sandia ’ should be removed. Other similar problems in the text also need to be modified.

-All the space in the paper is removed.

P4-L157: In the sentence ‘ It produces an average daily drinking water of 2m3 per day ’ ,for the‘ 2m3 ’ 3 should be superscript. Other similar problems in the text also need to be modified.

All m³ is superscripted corrected

P5-L213:There is a blank section above the heading "2.1 Materials and methods", which should be removed.

The empty section above the heading "1 Materials and methods" is deleted.

P6-L232:The explanation of Figure 3 is a not professional enough. It is suggested to label the two pictures a and b in sequence and give a more detailed explanation.

-Characteristics of the PV modules used and features of the solar inverter, battery and controller in the PV system are presented in the tables 2 and 3.

-The following paragraph is added in the section (2.2. Solar desalination system):

As shown in figure 4, using a low-pressure pump, the feed water is pumped to sand as a pre-filter which provides a first filtration stage to remove larger particles in the water, then some form of activated carbon to remove odors and other compounds followed by microfiltration. The high-pressure pump HP is then connected to the RO unit membrane to provide the pressure driving force needed to facilitate desalination through the RO semi-permeable membrane. The low and high-pressure pumps are powered by a solar photovoltaic system during the daytime. The surplus electricity provided by the PV panels during the day is stored in batteries that can power the pumps at night.

P10-L400:Text after subheading 3.1 should be below Table 3,the current format is crowded. Other similar problems in the text also need to be modified.

All similar problems are solved in the revised paper.

P11-L456:Fig.7, 8should be properly centered.

All figures are replotted and properlycentered

P14-L513:Fig.14,The two images shown are not at the same height so they should be lined up and numbered in order. Other similar problems in the text also need to be modified.

All figures are correctly modified and improved

P16-L540:The information in Table 5 is stacked with rows causing confusion and needs to be modified.

Table 5 is modified.

P21-L661:The format of the references cited in the article should agree with international standard.

New references are added and others are deleted.
The references cited in the article now are agree with international standard.

Finally, the author should give some examples of other materials used in desalination for electricity generation from new energy sources.

-We added small paraph in section 2 by citing other materials used in desalination for electricity generation from new energy sources(wind energy, wave energy, blue energyand geothermal energy).

In fact, there are other renewable energy options accessible worldwide[44]. Wind[45], wave[46,47], geothermal[48,49], and blue energy[50, 51], also known as osmotic power, are the primary sustainable energy sources used for desalination.

- Some references related to this topic are added in the revised paper as below:

[44]Hesham R. Lotfy, Jan Staš, Hynek Roubík.Renewable energy powered membrane desalination: reviewof recent development.Environmental Science and Pollution Research (2022). 29:4655246568.https://doi.org/10.1007/s11356-022-20480-y

[45]Vujcic R, Kmeta M (2000) Wind-driven seawater desalination plant for agricultural development on the islands of the County of Split and Dalmatia. Renewable Energy 19:173–183.

[46]B. Del Río-Gamero , Tyrone Lis Alecio , J. Schallenberg-Rodríguez. Performance indicators for coupling desalination plants with wave energy. Desalination.Volume 525, 1 March 2022, 115479.

[47]Viola A, Franzitta V, Trapanese M, Curto D, Viola D (2016) Nexus water & energy: a case study of wave energy converters (WECs) to desalination applications in Sicily. Int J Heat Technol. 34(2):S379–S386https://doi.org/10.1016/j.desal.2021.115479.

[48]Mahmoudi H, Spahis N, Goosen MF, Ghaffour N, Drouiche N, Ouagued A (2010) Application of geothermal energy for heating and freshwater production in a brackish water greenhouse desalination unit: a case study from Algeria. Renew Sustain Energy Rev 14:512–517.

[49]Kalogirou SA (2015) (2005) Seawater desalination using renewable energy sources. Prog Energy Combust Sci 31:242–281. https://doi. org/ 10. 1016/j. pecs. 2005. 03. 001.

[50]Post JW, Goeting CH, Valk J, Goinga S, Veerman J, Hamelers HVM, Hack PJFM (2010) Towards implementation of reverse electrodialysis for power generation from salinity gradients. Desalin Water Treat 16:182–193.

[51]Veerman J, Saakes M, Metz SJ, Harmsen GJ (2010) Electrical power from sea and river water by reverse electrodialysis: a first step from the laboratory to a real power plant. Environ Sci Technol. 44(23):9207–9212.

Round 2

Reviewer 1 Report

This MS is an improvement on its predecessor.

1. Line 135 should be 2020 not 2024

2. Line 140. I assume that this is Pakistan Rupees as the currency, please could you, for clarity add a conversion to a US currency. At the current exchange rate of 1PKR = 0.0036 USD, this cost is USD2.59/m3 (determined in 2020).

3. Table 3 - Please change all word in French to English

Why did you decide to use a 12V battery bank instead of a 2V AGM battery bank? I was looking for the following information for your battery bank

Specifications (per 2V battery cell):

Nominal voltage: 2V
Nominal capacity: 500Ah (10h rate) / 508Ah (20h rate)
Maximum charging current: 100A
Charging voltage: 2.2 - 2.35 V per 2 V cell
Cycle lifetime at 30% D.O.D.: 1200
Pressure control: safety valve installed
Terminal type: M10 bolts
Operating temperature: from -10C to +40C
Size: 242 x 174 x 365 mm
Weight: 27 kg

Specifications (entire 48V battery bank):

Nominal voltage: 48V
Nominal capacity: 24kWh
Maximum charging current: 100A
Charging voltage: cycle use 56.4V, standby use 54.8V
Temperature compensation: cycle use -120mV/°C, standby use -72mV/°C
Size: 1290 x 1140 x 670 mm (when positioned in racking)
Weight: 720 kg (including racking)

I was looking for the model of the MPPT controller and the Victron charge controller used to be specifically identified in the Table or text

4. Figure 4, please give the inverter model used and the model, operating details, and energy requirement (kWh) of the pump used - this is to allow reproducibility of your study. Please note what happened to the reject brine at this point. Earlier in the introduction you note that the system is intended to produce 2 m3/d. In Table 4 you note that the membrane can handle 6.6 m3/d at capacity. Please note what the delivery rate to the membrane was from your high pressure pump. Was it 4 m3/d or 6.6 m3/d or something different

5. At around line 330 you should indicate the daily power consumption and the daily charge to the batteries and power recovered from the PV. You should have this information stored on your app associated with the Victron charge controllers. At my location a 3.6 kW PV array actually generates <7 kWh/d. You need to give some indication of what you actually achieved in terms of generation, the amount stored each day and the amount used. It is also unclear if your panels are fixed to the building as shown in the photographs how they could have provided power during the day to your field location. Please clarify

6. Table 5 and throughout text please use a SI notation for numbers. You use a French notation which expresses a decimal point as a comma. The SI notation replaces the comma with a full stop. Please also convert words which are written in French, e.g. chlorure, to their English equivalent.

7. I have problems with your numbers in Table 5

You either have an error on your TDS values or your salinity values or both. Salinity is included within TDS in standard measurements, and salinity is <=TDS. In your table TDS is always less than salinity. I have difficulty in understanding how in waters 2 to 5 the chloride concentration is greater than both the salinity and TDS. I think that you need to add a section to the methodology section indicating the methods and equipment used (together with calibration standards) for each item listed in Table 5. Otherwise the reader will have difficulty with understanding this table.

The Table 5 numbers are not consistent with the feed water numbers in Figures 17 and 18 - they should be. There is an error somewhere.

8. Table 7 - bacterial methodology used to create these values should be provided and described in the methodology section. Is UFC the same as CFU - please clarify in the table caption.

9. Line 413 - Please add an average or typical graph showing for a 24 h period the amount of energy being generated kWh, since you have a data set for every 10 minutes, at around this location. This will supplement Figs 7 and 8

10. Line 458 - should 02 be 20?

11. Line 468. The meaning is not clear. Is this 2 batteries or batteries supplying sufficient energy for 2 days

12. Fig 10 caption - please add the following information to the caption: (i) feed water supplied L/h or another unit in each example; (ii) relationship between pressure (bar) and pump energy required (kwh). Is this relationship constant or does it vary with salinity

13. Figure 11 - y-axis caption is wrong, please correct make consistent with the text and figure caption

14. Figure 12 - please add a clarification to the caption of the form: Concentrate flow = feed water; Permeate flow = desalinated product water - this is for clarity.

15. Line 558 - table number is wrong - see also line 563

16 Line 559 - the value of 30.2 g/L is wrong and does not relate to the 5 water samples. It should it be 20 g/L or 35 g/L?

17. Line 563. Add feed water salinity to the caption together with the feed water flow rate L/h, permeate flow rate L/h, and retentate flow rate L/h. In this table the measured chloride values are not consistent with the salinity. I would have expected in the retentate >40 g Cl/L, if your salinity value is corrected. Please document in the methodology the equipment, methods and calibrations used for each chemical and biological measurement

18. Line 586 - 590 Table number is incorrect. This mislabeled Table 6 is interesting. It raises a question as to how many solar panels and battery storage units do you require to actually power the unit for 24 h. Please use the data you have from your PV panels + battery storage to provide two separate tables where you duplicate the mislabeled table 6, but in one table you replace kw with number of PV panels, and in the other you replace kW with the number of kWh of battery storage required for 24 h operation where 1 kWh = x batteries.

19. Line 655 - please add the feed water salinity to the table caption - check the table numbering throughout the ms

Author Response

Ref. ID: sustainability-2215470

Title: Feasibility study of a reverse osmosis desalination unit powered by

photovoltaic panels for a sustainable water supply in Algeria

Corresponding author: Seif El Islam Lebouachera, Nadjib Drouiche

Cover letter

Dear Editor,

The paper is reworked and modified according to the comments of the reviewers. In the second revised paper, we give changes that are clearly indicated in Green.

We give below a separate point-by-point response to each comment. Each of the reviewers comments is listed (in black) followed by our response (in blue).

Reviewer 1

Comments and Suggestions for Authors

This MS is an improvement on its predecessor.

Line 135 should be 2020 not 2024

All years of publication are removed from the revised manuscript (it is requested from the second reveiwer)

Line 140. I assume that this is Pakistan Rupees as the currency, please could you, for clarity add a conversion to a US currency. At the current exchange rate of 1PKR = 0.0036 USD, this cost is USD 2.59/m3 (determined in 2020).

The cost per liter of desalinated water was calculated to be USD 0.002592 with a total monthly profit of USD 194.4.

Table 3 - Please change all word in French to English

-All words in French are changed to English.

Why did you decide to use a 12V battery bank instead of a 2V AGM battery bank? I was looking for the following information for your battery bank

The dimensioning of the PV system requires 12 V battery bank. We bought these AGM batteries from the Algerian supplier Condor.

Specifications (per 2V battery cell):

Nominal voltage: 2V
Nominal capacity: 500Ah (10h rate) / 508Ah (20h rate)
Maximum charging current: 100A
Charging voltage: 2.2 - 2.35 V per 2 V cell
Cycle lifetime at 30% D.O.D.: 1200
Pressure control: safety valve installed
Terminal type: M10 bolts
Operating temperature: from -10C to +40C
Size: 242 x 174 x 365 mm
Weight: 27 kg

Specifications (entire 48V battery bank):

Nominal voltage: 48V
Nominal capacity: 24kWh
Maximum charging current: 100A
Charging voltage: cycle use 56.4V, standby use 54.8V
Temperature compensation: cycle use -120mV/°C, standby use -72mV/°C
Size: 1290 x 1140 x 670 mm (when positioned in racking)
Weight: 720 kg (including racking)

I was looking for the model of the MPPT controller and the Victron charge controller used to be specifically identified in the Table or text

The MPPT system technology is integrated in all systems used in our work (Condor charge controller, Victron inverter) as shown in table.3 ;

Figure 4, please give the inverter model used and the model, operating details, and energy requirement (kWh) of the pump used - this is to allow reproducibility of your study.

The inverter model used is given in the Table 3.

Operating details, and energy requirement (kWh) of the pump used is presented in the section (2.3) (see lines 407-409). This is summarized in the following table:

High pressure pump characteristics

Voltage and current	400V-3,7Amp
Pump speed	1700t / m
Rated mechanical power	1LkW
Power factor (Cos)	0,77
Electric power	1,8KW≈2
Pump output	11.5 liters per minute (1420TPM)

Please note what happened to the reject brine at this point. Earlier in the introduction you note that the system is intended to produce 2 m3/d. In Table 4 you note that the membrane can handle 6.6 m3/d at capacity.

The system has been designed for a production of 2m 3/d. The production depends on the flow rate of the HP pump, and in our case, the raw water consumption is about 200 L/h to produce 2m3/d.

Please note what the delivery rate to the membrane was from your high pressure pump. Was it 4 m3/d or 6.6 m3/d or something different

The flow rate from the high pressure pump to the membrane is 4 m3/d.

At around line 330 you should indicate the daily power consumption and the daily charge to the batteries and power recovered from the PV.

We added in the MS (Line 370 in the revised MS) all the information requested as follows :

The daily power consumption is 8KW/d, the daily charge to the batteries is 952 Ah and power recovered from the PV is 3000W.

-At my location a 3.6 kW PV array actually generates <7 kWh/d. You need to give some indication of what you actually achieved in terms of generation, the amount stored each day and the amount used. It is also unclear if your panels are fixed to the building as shown in the photographs how they could have provided power during the day to your field location. Please clarify

In our case, we have assumed that the number of operating hours is only 4h/d in order to minimise the photovoltaic field. The information is given in the MS : line 406. The PV panels attached to the building only provide electricity for 4 hours per day to our system.

Table 5 and throughout text please use a SI notation for numbers. You use a French notation which expresses a decimal point as a comma. The SI notation replaces the comma with a full stop. Please also convert words which are written in French, e.g. chlorure, to their English equivalent.

-We have corrected all (,) we used a SI notation for all numbers

- I have problems with your numbers in Table 5You either have an error on your TDS values or your salinity values or both. Salinity is included within TDS in standard measurements, and salinity is <=TDS.In your table TDS is always less than salinity. I have difficulty in understanding how in waters 2 to 5 the chloride concentration is greater than both the salinity and TDS.

- We coorected the erros of TDS values and salinit and conductivity

- We verified and corrected the errors of TDS values, salinity and conductivity, it wa a copy mistake in the table.

-We used a volumetric method for the determination of calcium, magnesium alkalinity and chloride ions. The Hach multiparameters instrument is used for the determination of TDS and salinity.

-The Table 5 numbers are not consistent with the feed water numbers in Figures 17 and 18 - they should be. There is an error somewhere.

-The figure 17 and 18 are replotted

-Table 7 - bacterial methodology used to create these values should be provided and described in the methodology section. Is UFC the same as CFU - please clarify in the table caption.

-Bacterial methodology used is provided and described in the methodology section as below

The membrane filtration technique is used to detect, identify, and count indicator microorganisms in the water sample. An appropriate volume of the sample is filtered through a Millipore membrane with a pore size of 0.45 mm. The membrane is incubated on an agar plate. Bacterial cells trapped on the membrane will grow into colonies that can be counted, and a bacterial density can be calculated. The number of visible colonies (CFU) present on a plate can be multiplied by the dilution factor to provide the CFU/ml value.

- Line 458-should 02 be 20?

- 20 modules

- Line 468. The meaning is not clear. Is this 2 batteries or batteries supplying sufficient energy for 2 days

The meaning is : batteries supplying sufficient energy for 2 days

We have changed the sentence meaning by « Batteries supplying sufficient energy for 2 days ».

-Fig 10 caption - please add the following information to the caption: (i) feed water supplied L/h or another unit in each example; (ii) relationship between pressure (bar) and pump energy required (kwh). Is this relationship constant or does it vary with salinity.

-In Fig 10 caption, we added the Permeate recovery R% , Conversion rate of feed water is defined by the following Equation: R = 100 * (Qp / Qf), where R is recovery rate, %, Qp is the product water flow rate, and Qf is the feed water flow rate.

The relationship between pressure and pump energy required is presented in table 8.

This relationship relatively constant with salinity because we have the same flow rate of HP pump.

- Figure 11 - y-axis caption is wrong, please correct make consistent with the text and figure caption.

y-axis caption is corrected in figure 11.

- Figure 12 - please add a clarification to the caption of the form: Concentrate flow = feed water; Permeate flow = desalinated product water - this is for clarity.

-We added in figure 12 a clarification to the caption as requested .

- Line 558 - table number is wrong - see also line 563

-All number table are corrected

- Line 559 - the value of 30.2 g/L is wrong and does not relate to the 5 water samples. It should it be 20 g/L or 35 g/L?

-The value is corrected 35g/L

- Line 563. Add feed water salinity to the caption together with the feed water flow rate L/h, permeate flow rate L/h, and retentate flow rate L/h.

Feed water salinity is added to the caption together with the feed water flow rate L/h, permeate flow rate L/h, and retentate flow rate L/h

-In this table the measured chloride values are not consistent with the salinity. I would have expected in the retentate >40 g Cl/L, if your salinity value is corrected. Please document in the methodology the equipment, methods and calibrations used for each chemical and biological measurement

- The measured chloride value is corrected in the table7

- Line 655 - please add the feed water salinity to the table caption - check the table numbering throughout the ms

-The feed water salinity is added to the table caption and all table numbering throughout the MS are checked.

Reviewer 2 Report

Accept in present form

Author Response

Ref. ID: sustainability-2215470

Title: Feasibility study of a reverse osmosis desalination unit powered by

photovoltaic panels for a sustainable water supply in Algeria

Corresponding author: Seif El Islam Lebouachera, Nadjib Drouiche

Cover letter

Dear Editor,

The paper is reworked and modified according to the comments of the reviewers. In the second revised paper, we give changes that are clearly indicated in Green.

Reviewer 3 Report

The manuscript titled “Feasibility study of a reverse osmosis desalination unit powered by photovoltaic panels for a sustainable water supply in Algeria” and written by Zahia Tigrine et al. has too many drawbacks. I recommend a rejection based on the following comments (paper should be restructured and rewritten):

11. Page 2, line 65. Reverse osmosis was abbreviated so use the abbreviation in line 80, 81, 86.. Revise the entire manuscript and for all the abbreviations made.

22. Page 2, lines 81-83. Authors mentioned recovery and specific energy consumption. These values depend on the water to be desalinated. Lower specific energy consumption is found in brackish water due to lower osmotic pressure in comparison with seawater. This can be supports by published studies (Desalination, 491, 114569; Desalination 491, 114582).

33. Page 3, line 135. What’s the meaning of 2024? The year of the publication should not be written according with the citation style of the journal. Please revise the entire manuscript.

44. The author did not remark the challenges of operating RO systems powered by renewable energy such as variable operation and intermittency. This should be commented (Computers & Chemical Engineering 153, 107441; Desalination, 532, 115715; Desalination 489, 114526; Journal of Membrane Science, 647, 120286; Desalination, 494, 114669; Applied Sciences 10 (14), 4748).

55. The paragraph from page 3, line158 till page 4 line165 does not have any reference that support the information. Same in the following paragraph. This is not appropriate.

66. Page 4, line 192. Number 2 must be written as superscript. Revise the entire document.

77. Page 4, line 208, write SWDP between brackets.

88. Last paragraph of page 4. Please, add reference/s that support the information provided.

99. Page 5, line 230. Please, provide space between number and unit. 3 kWp. Revise the entire manuscript.

110. The structure of the paper must be changes to usual structure, introduction, material and methods, results, discussion and conclusions.

111. In section 2 there are information that it does no belong to the section. This section should be rewritten. Section 2 – solar powered desalination unit should be removed. Material and methos should be a section instead of subsection.

112. Table 4 is a copy of the membrane manufacture datasheet. This is not admissible.

113. Was the Figure 4 made by the authors? If not, the authors should include the reference from where it was taken.

114. There is information in material and methods that is not suitable here. In this section include detailed information. The reader should be able to reproduce the experiment, methods, identify the equipment and materials used and nothing else.

115. According with the Table 5, the authors used brackish water and seawater. It does not make any sense, the requirements for brackish are completely different than for seawater in terms on membrane (SW or BW RO membrane element), feed pressure and recovery.

Author Response

Ref. ID: sustainability-2215470

Title: Feasibility study of a reverse osmosis desalination unit powered by

photovoltaic panels for a sustainable water supply in Algeria

Corresponding author: Seif El Islam Lebouachera, Nadjib Drouiche

Cover letter

Dear Editor,

The paper is reworked and modified according to the comments of the reviewers. In the second revised paper, we give changes that are clearly indicated in Green.

We give below a separate point-by-point response to each comment. Each of the reviewers comments is listed (in black) followed by our response (in blue).

Reviewer 3

Comments and Suggestions for Authors

- Page 2, line 65. Reverse osmosis was abbreviated so use the abbreviation in line 80, 81, 86. Revise the entire manuscript and for all the abbreviations made.

All the abbreviations are made in the MS.

- Page 2, lines 81-83. Authors mentioned recovery and specific energy consumption. These values depend on the water to be desalinated. Lower specific energy consumption is found in brackish water due to lower osmotic pressure in comparison with seawater. This can be supports by published studies (Desalination, 491, 114569; Desalination 491, 114582).

We added the following sentences in the MS to clarify more the meaning:

-The major drawback is that it still consumes energy despite the integration of energy recovery systems. This depends on the water to be desalinated, a lower specific energy consumption is found in brackish water (BWRO) due to a lower osmotic pressure compared to seawater [12,13]. The energy requirements for BWRO and SWRO are approximately 1-1.5 kWh/m3 and 3-4 kWh/m3, respectively.

-We added the following references:

[12] Haya Nassrullah, Shaheen Fatima Anis , Raed Hashaikeh , Nidal Hilal. Energy for desalination: A state-of-the-art review. Desalination 2020,Volume 491, 114569. https://doi.org/10.1016/j.desal.2020.114569.

[13] Ruiz-García, A.; Nuez, I.; Carrascosa-Chisvert, M.D.; Santana, J.J. Simulations of BWRO systems under different feedwater characteristics. Analysis of operation windows and optimal operating points. Desalination 2020, 491, 114582. https://doi.org/10.1016/j.desal.2020.114582.

- Page 3, line 135. What’s the meaning of 2024? The year of the publication should not be written according with the citation style of the journal. Please revise the entire manuscript.

All years of publication are removed from the revised manuscript.

- The author did not remark the challenges of operating RO systems powered by renewable energy such as variable operation and intermittency. This should be commented (Computers & Chemical Engineering 153, 107441; Desalination, 532, 115715; Desalination 489, 114526; Journal of Membrane Science, 647, 120286; Desalination, 494, 114669; Applied Sciences 10 (14), 4748).

We added a paragraph on the challenges of operating RO systems powered by renewable energy such as variable operation and intermittency, based on published studies as requested

We have added a paragraph on the operational difficulties of RO systems powered by renewable energy, such as variable operation and intermittency, based on published studies, as requested :

- Various factors need to be taken into account when designing brackish water reverse osmosis BWRO desalination plants with short operating times, such as those powered by renewable energy sources [31,32]. Many published works have studied the impact of operating parameters and SEC in intermittent mode (during solar irradiance fluctuation) and its fluctuations on the performance of a BWRO desalination plant during operation and, consequently, on osmotic backwash and membrane fouling [33-36]. The evolution of operating parameters and the ideal SEC over a long period of intermittent operation with constant water production has been carried out and investigated in the relevant work of A. Ruiz-García and I. Nuez [31,33], [34]. The objectives are to provide a long-term performance analysis of a large-scale BWRO desalination plant operating intermittently without membrane replacement. Other variable renewable energy sources for powering RO desalination, with a case study of wave powered desalination for Kilifi, Kenya and experimental data on a commercial RO system are presented by Jennifer Leijon et al [33]. They discuss detail the possibility of using wave energy converters (WECs) to power RO systems. It is found that the power output of a WEC studied in this work is estimated to be 7 kW and it would be sufficient to power a suitably sized RO system.

[31] A. Ruiz-García and I. Nuez . On-Off Control Strategy in a BWRO System under Variable Power and Feedwater Concentration Conditions. Appl. Sci. 2020, 10(14), 4748. https://doi.org/10.3390/app10144748.

[32] A. Ruiz-García, I. Nuez. Long-term intermittent operation of a full-scale BWRO desalination plant. Desalination 489 (2020) 114526. https://doi.org/10.1016/j.desal.2020.114526

[33] Jennifer Leijon, Dana Salar, Jens Engström, Mats Leijon, Cecilia Boström. Variable renewable energy sources for powering reverse osmosis desalination, with a case study of wave powered desalination for Kilifi, Kenya. Desalination 494 (2020) 114669. https://doi.org/10.1016/j.desal.2020.114669.

[34] A. Ruiz-García, I. Nuez. Performance evaluation and boron rejection in a SWRO system under variable operating conditions. Computers and Chemical Engineering 153 (2021) 107441. https://doi.org/10.1016/j.compchemeng.2021.107441

[35] Mohamed T. Mito, Xianghong Ma, Hanan Albuflasa, Philip A. Davies . Variable operation of a renewable energy-driven reverse osmosis system using model predictive control and variable recovery: Towards large-scale implementation .Desalination 532 (2022) 115715. https://doi.org/10.1016/j.desal.2022.115715

[36] Yang-Hui Cai, Claus J. Burkhardt , Andrea I. Schäfer. Renewable energy powered membrane technology: Impact of osmotic backwash on organic fouling during solar irradiance fluctuation. Journal of Membrane Science Volume 647, 2022, 120286. https://doi.org/10.1016/j.memsci.2022.120286

- The paragraph from page 3, line158 till page 4 line165 does not have any reference that support the information. Same in the following paragraph. This is not appropriate.

-References below are added in this paragraph to support the information

-The following references are repositioned in the text :

[36] Youcef Himri ,Shafiqur Rehman ,Ali Mostafaeipour ,Saliha Himri ,Adel Mellit ,Mustapha Merzouk and Na-769 chida Kasbadji Merzouk. Overview of the Role of Energy Resources in Algeria’s Energy Transition.Energies 2022, 770 15(13), 4731; https://doi.org/10.3390/en15134731.

[48] Mahmoudi H, Spahis N, Goosen MF, Ghaffour N, Drouiche N, Ouagued A (2010) Application of geothermal energy for heating and freshwater production in a brackish water greenhouse desalination unit: a case study from Algeria. Renew Sustain Energy Rev 14:512–517

[29] N. Drouiche, N. Ghaffour, M. Naceur, Hacène Mahmoudi, Tarik Ouslimane Reasons. for the Fast Growing Sea water Desalination Capacity in Algeria. Water Resources Management. (2011) 25,pp2743-2754.

[31] Ait Mimoune Hamiche, A. Boudghene Stambouli, S. Flazi, A. Tahri & H. Koinuma . Desalination in Algeria: 755 Current State and Recommendations for Future Projects. Thermo-Mechanics Applications and Engineering Tech-756 nology, 2018. ISBN : 978-3-319-70956-7.

- Page 4, line 192. Number 2 must be written as superscript. Revise the entire document.

- Number 2 is written in superscript and the whole document is revised.

- Page 4, line 208, write SWDP between brackets.

(SWDP) is rewritten between brackets

- Last paragraph of page 4. Please, add reference/s that support the information provided.

-Two references below are added in last paragraph of page 4 to support the information provided.

- Page 5, line 230. Please, provide space between number and unit. 3 kWp. Revise the entire manuscript.

We have provided space between number and unit in the entire manuscript.

- The structure of the paper must be changes to usual structure, introduction, material and methods, results, discussion and conclusions.

-The structure of the paper is changed to usual structure (introduction, material and methods, results, discussion and conclusions).

- In section 2 there are information that it does no belong to the section. This section should be rewritten. Section 2 – solar powered desalination unit should be removed. Material and methos should be a section instead of subsection.

Section 2.solar powered desalination unit is moved as subsection after Section Material and methos

- Table 4 is a copy of the membrane manufacture datasheet. This is not admissible.

Table.4 has been redone and reprocessed.as presented below:

Membrane Element

SWC5-LD-4040

(Low Fouling Technology)

Performance :

Permeate Flow :

Salt Rejection :

1,750 gpd (6.62 m³/d) 99.7% (99.5% minimum)

Type

Configuration :

Membrane Polymer:

Membrane Active Area :

Feed Spacer :

Low Fouling Spiral Wound

Composite Polyamide

80 ft2 (7.43 m²)

34 mil (0.864 mm)

Application Data*

Maximum Applied Pressure :

Maximum Chlorine Concentration :

Maximum Operating Temperature:

pH Range, Continuous (Cleaning):

Maximum Feedwater Turbidity:

Maximum Feedwater SDI (15 mins):

Maximum Feed Flow :

Minimum recovery rate for any Element:

Maximum Pressure Drop for Each Element:

600 psig (4.14 MPa)

< 0.1 PPM

113 °F (45 °C)

2-11 (1-13) *

1.0 NTU

5.0

16 GPM (3.6 m³/h)

1O%

15 psi

* The limitations shown here are for general use. For specific projects, operating at more conservative values may ensure the best performance and longest life of the membrane. See Hydranautics Technical Bulletins for more detail on operation limits, cleaning pH, and cleaning temperatures.

A, inches (mm)	B, inches (mm)	C, inches (mm)	Weight, lbs. (kg)
40.00 (1016)	3.95 (100.3)	0.75 (19.1)	8 (3.6)

Table.4 Characteristics of membrane element SWC5-LD-4040 of the manufacturer Hydranautics

- Was the Figure 4 made by the authors? If not, the authors should include the reference from where it was taken.

Yes, Figure 4 is made by the authors

- There is information in material and methods that is not suitable here. In this section include detailed information. The reader should be able to reproduce the experiment, methods, identify the equipment and materials used and nothing else.

Some information in material and methods that is not suitable here are moved.

Reviewer 4 Report

Some questions are as follows:

P4---L191:In the sentence ‘The energy daily received on a horizontal surface of 1m2 is of the order of 5 kWh over most of the national territory ’ ,for the‘ 1m2 ’ 2 should be superscript. Other similar problems in the text also need to be modified.

p8---L308:Table 4 is a blurry picture with incomplete information and needs to be reprocessed.

P10---L357:The information in Table 5 is stacked with rows causing confusion and needs to be modified.

P21-L661:The format of the references cited in the article should agree with international standard.

Author Response

Ref. ID: sustainability-2215470

Title: Feasibility study of a reverse osmosis desalination unit powered by

photovoltaic panels for a sustainable water supply in Algeria

Corresponding author: Seif El Islam Lebouachera, Nadjib Drouiche

Cover letter

Dear Editor,

The paper is reworked and modified according to the comments of the reviewers. In the second revised paper, we give changes that are clearly indicated in Green.

We give below a separate point-by-point response to each comment. Each of the reviewers comments is listed (in black) followed by our response (in blue).

Reviewer 4

Comments and Suggestions for Authors

Some questions are as follows:

P4---L191: In the sentence ‘The energy daily received on a horizontal surface of 1m2 is of the order of 5 kWh over most of the national territory ’ ,for the‘ 1m2 ’ 2 should be superscript. Other similar problems in the text also need to be modified.

Number 2 is superscripted in the text and all other similar problems is modified.

p8---L308:Table 4 is a blurry picture with incomplete information and needs to be reprocessed.

Table 4 is reprocessed.

P10---L357: The information in Table 5 is stacked with rows causing confusion and needs to be modified.

Table 5 is modified.

P21-L661:The format of the references cited in the article should agree with international standard.

The format of the references cited in the article is correcte dit is agree with international standard

Round 3

Reviewer 1 Report

Thank you for considering my suggestions in the last revision round. I have no further suggestions regarding your ms

Reviewer 3 Report

The manuscript titled “Feasibility study of a reverse osmosis desalination unit powered by photovoltaic panels for a sustainable water supply in Algeria” and written by Zahia Tigrine et al. still has too many drawbacks to being considered to be published. I recommend rejecting this paper based on the following comments:

1. Generally, abstracts do not include periods.

2. Please, keep space between number and units. For example in page 1, line 45, write 35 g/L instead 35g/L. Revise the entire manuscript.

3. Page 2, lines 88-104. There are not references that give support to the sentences written on those lines. This is not admissible in a scientific article. Authors should include some references.

4. Page 5, lines 221-233. why authors use thousands separators in some numbers and not in others?

5. Page 5, line 256. According with the forma of the journal it should be written Figure 2 instead of figure.2. Please, revise the entire manuscript. In caption of figures, Figure 2. Must be written.

6. In Table 2, what is à? Revise this.

7. In the beginning of section 2 it is written what RO membrane and RO process are. The authors repeat at the beginning of subsection 2.1. This is redundant information. The authors must avoid this, revise the entire manuscript. The material and methods section must include information about the material used and the methods used in the experimental. This should allow other researchers to make the same experiments. Do not include sentences about the more efficient process, etc..

8. The work photovoltaic was abbreviated in page 3, line 110. From this point the authors must write the abbreviation. Revise the entire manuscript.

9. In Figure 4, Are the authors sure that the inverter is correct? As much as I know the DC should be in the side of the battery, and the AC to the electrical engine.

10. Why does the pilot plant not have microfiltration stage? It is weird to connect from sand filters to carbon filter.

11. Why the authors used a seawater membrane to treat brackish water (water 1 and 2 in table 5)? Seawater membrane have higher solute rejection, but the specific energy consumption is higher than brackish water RO membranes?

12. Page 12, line 477. The authors wrote that Fig 8 shows the evolution of the estimate of the monthly solar radiation. I do not understand this sentence. Beside this, Fig 8 shows a solar radiation and temperature per hour. Is this an average of the whole year or just measurements of a single day?

13. Title of section 3.1 should be RO membrane performance.

14. Page 14. Authors wrote Figure 10 and Fig.10. in the same paragraph. Please, the writing must be uniform. Revise the entire manuscript.

15. According with the Figure 3, there is one spiral wound membrane element in the desalination plant. How is possible that Figure 10 shows flux recoveries that high considering that the maximum flux recovery for SWRO membrane elements are around 30%?

16. Page 15, line 563, include the reference for the document of the WHO.

17. Figures 12, 13 and 14 show low rejection flows. For a 4 inches spiral wound membrane module, the minimum rejection flow established by membrane manufacturers is 0.5, usually 0.7 m3/h. Have the authors considered this?

18. Revise the Table 7.

Author Response

Dear Editor,

The paper is reworked and modified according to the comments of the reviewers.

In the third revised paper, we give changes that are clearly indicated in Yellow.

We give below a separate point-by-point response to each comment. Each of the reviewers comments is listed (in black) followed by our response (in blue).

Please see attached file

Author Response File: Author Response.pdf