Review Reports - The Cost of Brine Dilution in the Desalination Plants of Alicante

Round 1

Reviewer 1 Report

There is not enough scientific novelty in this manuscript.

Author Response

We do not agree with this reviewer. Brine dilution has been recently proposed as one way to meet sustainable desalination (Sola et al 2020) but it implies energy consumption that has not been previously evaluated. In this manuscript we evaluate for the first time the cost of brine dilution to meet environmental requirements

Reviewer 2 Report

I have no further comments on the work done

Author Response

We thank previous comments of this reviewer that have contributed to improve our manuscript

Reviewer 3 Report

Interesting paper. The MS could be improved by the following additions:

Adding a location map showing the various components of the plant mentioned in the text, plant, ponds, inflow and outflow pipes, location of the sensitive seagrass beds which you are trying to protect location of the seawater extraction pipes for dilution.
Adding a table or graph to supplement Figure 2 providing: (i) volume of seawater abstracted to make the desalinated water (including salinity), volume of raw brine produced (and salinity), volume of dilution water abstracted and salinity, volume of diluted brine produced (and salinity). Note the product water salinity associated with each year in Fig 2. Was it 0 g/L or something higher?
The relationship between the dilution ratio and product water salinity - if you have product water and seawater pH please include them, together with the average feedwater and discharge water temperature,. One of the issues at your location is whether the discharge is solely responsible for the seagrass decline. Could other discharges, fishing practice etc also have contributed to the decline - suggest that you address this issue before the conclusions.
Line 219 - Not clear why abstraction of seawater should alter the groundwater level. If this is not a mistake, please in your description of the plant describe how and why the abstraction of seawater affects the local groundwater levels. I am assuming from your wording that you are not referring to seawater infringement into the aquifer.
Line 220 - you need under the plant description to describe the irrigation project for the saltmarsh including area covered, nature of the scheme the amount of water involved, where it is from, brine, diluted brine, etc, and the salinity of the irrigation water (and seawater in the marsh), and whether the irrigation is actually diluting the salinity of water in the saltmarsh. In my experience the salinity of water in the saltmarsh can naturally be 5 to 15 g/L higher than that in seawater, and will locally reach supersaturation salinities during low tide
Is it possible to update the paper to include 2019/21 data?
These additions will make the paper easier to read (and more useful) for an international audience.

Author Response

Interesting paper. The MS could be improved by the following additions:

Adding a location map showing the various components of the plant mentioned in the text, plant, ponds, inflow and outflow pipes, location of the sensitive seagrass beds which you are trying to protect location of the seawater extraction pipes for dilution.

A new figure have been prepared

Adding a table or graph to supplement Figure 2 providing: (i) volume of seawater abstracted to make the desalinated water (including salinity), volume of raw brine produced (and salinity), volume of dilution water abstracted and salinity, volume of diluted brine produced (and salinity). Note the product water salinity associated with each year in Fig 2. Was it 0 g/L or something higher?

A table with requested information has been prepared as supplementary material. Salinity of product water is almost 0.

The relationship between the dilution ratio and product water salinity - if you have product water and seawater pH please include them, together with the average feedwater and discharge water temperature,. One of the issues at your location is whether the discharge is solely responsible for the seagrass decline. Could other discharges, fishing practice etc also have contributed to the decline - suggest that you address this issue before the conclusions.

We do not have product water and seawater pH. Feedwater and discharge water temperatures are quite similar and have a seasonal variation. Yes, other causes have contributed to the decline of seagrasses. A new paragraph has been included explaining the different impacts that suffer seagrass meadows in the area.

Line 219 - Not clear why abstraction of seawater should alter the groundwater level. If this is not a mistake, please in your description of the plant describe how and why the abstraction of seawater affects the local groundwater levels. I am assuming from your wording that you are not referring to seawater infringement into the aquifer.

The intake systems include beach wells and it has been observed that that may produce a lowering of the ground water level that affects the saltmarsh. An irrigation system has been established to protect the saltmarsh. See Navarro & Sánchez Lizaso (2021) for details.

Line 220 - you need under the plant description to describe the irrigation project for the saltmarsh including area covered, nature of the scheme the amount of water involved, where it is from, brine, diluted brine, etc, and the salinity of the irrigation water (and seawater in the marsh), and whether the irrigation is actually diluting the salinity of water in the saltmarsh. In my experience the salinity of water in the saltmarsh can naturally be 5 to 15 g/L higher than that in seawater, and will locally reach supersaturation salinities during low tide

The irrigation project has been described in Navarro & Sánchez Lizaso 2021

Is it possible to update the paper to include 2019/21 data?

Some data are not available at this moment. It will take us a lot of time to obtain the data for the period 2019-2021

These additions will make the paper easier to read (and more useful) for an international audience.

Thanks for your useful comments

Author Response File: Author Response.pdf

Reviewer 4 Report

This paper aims at providing an interesting return of experience of brine dilution for disposal of the desalination plant of Alicante. This type of study is of interest as it gives valuable feedback on implemented technology and their optimisation to fulfil the requirements. However, the scientific quality of this manuscript should be improved to get a clear analysis and be of valuable interest for the community.

Here are my main concerns:

All figures/tables are basic excel figures that should be modified to look more professional
All numbers should be revised to be more readable and with the adequate numbers of digits
More advanced analysis should be provided regarding the cost of the technology, impact of dilution rate and production capacity

Here are some more specific points that are example of points to be improved/clarified:

Abstract:

Simplify the numbers so that they are more readable
Why such a high variation of energy in-between years? If because of change of production maybe better express energy per m³ of water produced.
Same comment regarding the dilution rate (2.7 to 7.5). Explain the rational and the desired optimised value.

Introduction:

L31: mixing of brine? With what 8seawater I guess) but be more specific
L38: bypassing seawater…again not very clear. Do you mean that seawater is pumped just to dilute the brine?
A slightly more expended review of return of experiences of brine disposal and other brine dilution system would bring some valuable information (including economics/energy and impact on ecosystem).

Materials and methods:

L92: any more measurable value regarding the statement’’enough turburlence’’? Reynolds number? What are the recommendation/usual values.
I do not understand how come the dilution rate is fluctuating so much if the pumps have variator and therefore can adapt the volume pumped to the capacity needed. Please make it clearer

Results

L117-118: minimum costs of t2014 seems more connected to the production which was low…In general, please provide costs per m3 produced/year. It may be more readable.
L123-125: again I do not understand this statement. It seems to me that the dilution unit works at fixed flowrate and therefore lower production of water means same energy costs…please explain better
Table 1: please simplify the numbers and I miss the €/m3 of water produced. Also what do you mean by total cost and average cost in the last columns? In general all figures and tables should be revised.

Discussion:

L182-184: Please be more specific.
L207: 38.5PSU of salinity?
L221-222: and what is the cost to protect Posidonia oceanica?

Conclusion:

Please be more critical on the results of the study, way to improve the system,etc…to better control the dilution rate and optimised the costs for example.

Author Response

Here are my main concerns:

All figures/tables are basic excel figures that should be modified to look more professional

New figures have been prepared

All numbers should be revised to be more readable and with the adequate numbers of digits

We have revised all the numbers following the suggestion

More advanced analysis should be provided regarding the cost of the technology, impact of dilution rate and production capacity

We have clarified these aspects.

Here are some more specific points that are example of points to be improved/clarified:

Abstract:

Simplify the numbers so that they are more readable

Done

Why such a high variation of energy in-between years? If because of change of production maybe better express energy per m³ of water produced.

The variation of energy is due to the changes in water produced and changes in the dilution ratio. Energy per m³ of water produced has a similar trend than dilution ratio.

Same comment regarding the dilution rate (2.7 to 7.5). Explain the rational and the desired optimised value.

We have tried to clarify it. The minimum dilution ratio is 2:1. It has been optimised in last years but in previous years a dilution ratio higher than necessary was reached.

Introduction:

L31: mixing of brine? With what 8seawater I guess) but be more specific

It has been clarified.

L38: bypassing seawater…again not very clear. Do you mean that seawater is pumped just to dilute the brine?

Yes, it is. We think it is clearly stated: “the mixing behavior can also be improved by bypassing seawater and mixing it with brine to reduce its salinity before its discharge to the marine environment”

A slightly more expended review of return of experiences of brine disposal and other brine dilution system would bring some valuable information (including economics/energy and impact on ecosystem).

A new paragraph has been added at the beginning of the discussion on experiences of brine disposal and the reduction of environmental impacts, however no other study quantify the energy consumption of a dilution system

Materials and methods:

L92: any more measurable value regarding the statement’’enough turburlence’’? Reynolds number? What are the recommendation/usual values.

We have monitored the mixing of the brine with seawater and we observed that there is a good mixing. If turbulence was not enough the result will be an stratified system with brine at the bottom that will make useless seawater by-passing

I do not understand how come the dilution rate is fluctuating so much if the pumps have variator and therefore can adapt the volume pumped to the capacity needed. Please make it clearer

Because the company operating the plants did not try to optimise the dilution ratio up to the last years. Now they realise of the advantages of optimising the dilution.

Results

L117-118: minimum costs of t2014 seems more connected to the production which was low…In general, please provide costs per m3 produced/year. It may be more readable.

The energy consumption is lower in 2013 but the cost was lower in 2014 due to a lower price of energy. Both years have a low water production. Cost per m3 produced/year is included in table 2

L123-125: again I do not understand this statement. It seems to me that the dilution unit works at fixed flowrate and therefore lower production of water means same energy costs…please explain better

Not necessarily but during 2013 and 2014 the decrease in production did not produce a similar reduction in dilution. This has changed in recent years optimising the dilution ratio.

Table 1: please simplify the numbers and I miss the €/m3 of water produced. Also what do you mean by total cost and average cost in the last columns? In general all figures and tables should be revised.

We have simplified the numbers in all the tables and figures. Total cost means total cost of the energy used for dilution and average cost is the average cost of the energy consumed that has been different for each year. €/m3 of water produced is in table 2. Tables and figures have been revised.

Discussion:

L182-184: Please be more specific.

We have tried to clarify

L207: 38.5PSU of salinity?

Yes, it refers to the Practical Salinity Unit scale

L221-222: and what is the cost to protect Posidonia oceanica?

We have clarified that it is the brine dilution cost to protect Posidonia oceanica meadows

Conclusion:

Please be more critical on the results of the study, way to improve the system,etc…to better control the dilution rate and optimised the costs for example.

We have modified the conclusions following reviewer’s suggestions

Author Response File: Author Response.pdf

Reviewer 5 Report

This problem is relevant for journal scope. The concept and aim are clearly defined. I could find some typing errors. The manuscript follows the formal regulations of MDPI journals.

I suggest the acceptance major revision.

Remarks, suggestions, questions

I suggest using rounding the representations (kWh and euro), e. g. thousands.
Please cite more papers from this journal at the last two years in the similar topic of this research.
The main remark: please emphasize the novelty side(s) of your manuscript.
Please take out Figure 4 from the manuscript.
Which are the main significant and less significant parameters in the case of total cost and the consumed energy for production?
Please compare your results with literature results.
The conclusion part is too short and general. Please expand it with specific information and explanations.

Author Response

This problem is relevant for journal scope. The concept and aim are clearly defined. I could find some typing errors. The manuscript follows the formal regulations of MDPI journals.

Thanks for your comments

I suggest the acceptance major revision.

Remarks, suggestions, questions

I suggest using rounding the representations (kWh and euro), e. g. thousands.

Numbers have been rounded

Please cite more papers from this journal at the last two years in the similar topic of this research.

There are no papers on the same topic. Some related paper from this journal has been cited.

The main remark: please emphasize the novelty side(s) of your manuscript.

We indicate that up to the moment the energy consumption of the dilution System has not been quantified both in the abstract and the introduction.

Please take out Figure 4 from the manuscript.

We removed the previous figure 4 from the manuscript

Which are the main significant and less significant parameters in the case of total cost and the consumed energy for production?

The amount of energy consumption for production is directly related with the amount of water produced. The amount of energy consumption and cost for dilution is related both with water production and the dilution ratio.

Please compare your results with literature results.

As we have explained before there are no similar results in literature about the evaluation of the cost of dilution since it has been done for the first time in this paper.

The conclusion part is too short and general. Please expand it with specific information and explanations.

We have expanded the conclusions.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

In my view the MS can be published in its current form without alteration

Reviewer 5 Report

Thank you very much for your professional answers. I suggest the acceptance in this present form for publication.

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 purpose of this study is to estimate the cost of the dilution of brine in the SWRO of Alicante. This topic is interesting while this manuscript is more like a report not an article because it can’t provide some scientific indications for readers. Detailed comments are as follows: 1. The title is too large for the actual purpose of this work. Environmental protection includes many aspects not only dilution of the brine. I suggest the authors should revise it. 2. The “Abstract” part is not good enough. It lacks the introduction of this kind of studies and the gap of this field. This abstract looks like a “case study”. Thus, it can’t provide enough scientific significance for the readers. Right now, this manuscript is more like a report not an article. 3. The “introduction” has the same problems as the “abstract”. Authors should include more data and references in the same research field. How about the techniques for environmental protection or brine dilution in other SWRO plants? What’ the cost of them? Such data can provide a good reference for readers. 4. The figures from Fig. 1to Fig. 5 are poorly prepared. The resolutions of them are too low and I can’t see much importance to show them. otherwise you can combine them into 1 figure? 5. Fig. 6, there is no name of coordinate axis. 6. There is no error bar in the figures?

Reviewer 2 Report

Check the following points:

1) Check the units, kwh, KWh,… etc… throughout the article and use the international system of units.

2) Table 1 on line 139. The data for energy consumed, for example, year 2016, is higher than 2017, however, production was not. You will have to justify what is happening in that table. Furthermore, energy prices are not understood as being worth less in 2016 than in 2017. It is understood that it is the price of energy consumed.

3) It should provide the energy that has been consumed in the desalination process, since it refers to percentages in the desalination process.

4) However, in 2013-2014, the reduction in production increased the dilution to more than 7: 1, and the consumption was close to 4%. Justify these changes as these values are not understood.

5) The adjustments you make do not add value to the job, figures 8 and 9.