Water-Energy-Food-Climate Nexus in an Integrated Peri-Urban Wastewater Treatment and Reuse System: From Theory to Practice

Round 1

Reviewer 1 Report

The manuscript presents a study on water-energy-food-climate nexus assessment across several water reuse scenarios. I found the paper very interesting, with excellent idea, especially introduction, and methods, however I was somewhat disappointed by the lack of actual results and result analysis. You have introduced methods for carbon, energy, water and different crop production, and then you calculated only the very basic scenarios, without further look at different crop production, across different levels of demand, etc. While the idea of the paper is excellent, in a present form, work looks like a conference extended abstract, rather than journal paper. You need to add more analysis of scenarios and results for this work to be complete.

See detailed comments below.

Line number	Comment
1.      Abstract	You should add some results to the abstract. It only discusses the ideas, but there are no specific outcomes of the paper in the abstract.
2.      Keywords	Don’t use the same keywords from title or abstract. Keywords are meant to increase the article’s searchability. Have a think what would someone type to find your work.
3.      LN137	Significant, instead of significative
4.      LN232	Section 3.1 about scenarios should go into methodology section.
5.      Table 4	I am not sure what are your assumptions for treatment for every class, since your nutrients are all the same. Is the only difference in disinfection level (and some minor differences in TSS and BOD)? If so, why is disinfection “star” level in Fig 1 all the same (even for non-reuse)?
6.      Table 3	What is “n” in E. coli unit? I have never seen that unit. It’s usually either CFU or MPN (depending on the method).
7.      Table 4 and Fig 1	These two things don’t seem to match. Water Reuse Class C seems the best for energy and carbon, but you gave class A the most stars in Fig 1. I don’t really understand this.
8.      Fig 1	What are these stars based on?

Author Response

Rensponses to the reviewer's comments are reported in the attached document

Author Response File: Author Response.pdf

Reviewer 2 Report

I would like to suggest some requests for changes and additions before positively evaluating the acceptance of this manuscript for publication in Sustainability.

In general, the bibliographic references must be increased in the text, as there are not many (ie line 33, 37, 40 etc.), both in the introduction and in subsequent chapters.

Line 55, Please enter a reference. I would like to suggest this:

Bassano, C .; Deiana, P .; Vilardi, G .; Verdone, N. Modeling and economic evaluation of carbon capture and storage technologies integrated into synthetic natural gas and power-to-gas plants. Appl. Energy 2020, 263, 114590, doi: 10.1016 / j.apenergy.2020.114590.

Line 112, 244, 253. I think it can also be very useful to provide a flow diagram of the water resources, the treatment plant and the distribution of water together with the irrigation systems, in order to make the text smoother.

Author Response

Rensponses to the reviewer's comments are reported in the attached document

Author Response File: Author Response.pdf

Reviewer 3 Report

I think his paper is good, informative, and well-organised. However, there are few spelling/grammar mistakes that must be removed before the final acceptance 

Author Response

Rensponses to the reviewer's comments are reported in the attached document

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for the effort in trying to revise the manuscript. However, there are still some major concerns about this manuscript. 

Your Methods are still lacking clarity. E.g. for carbon footprint assessment, you have a sentence that says: "Emissions were reported separately for each GHG when possible, as well as the distinction on the type of CO2, depending on its origin (i.e., fossil or biogenic)." But you don't report any type of CO2, other than cumulative. Also "For each  GHG, the emissions were multiplied by the respective Global Warming Potentials (GWPs) to obtain all the values expressed in CO2 equivalents [32]." - yet you don't provide any clarity what is the final equation used for Carbon footprint calculation from Table 4. It is very much the same for other calculations and assessments. You need to give equations which were used to produce final numbers, or at least which tool (computer program or whatever) you used for this. There is a lot of  

Table 2 - I assume that "efficiencies" means water loss factor; i.e. for 0.5 efficiency, you need double the amount of water to irrigate crop? If true, maybe clarify this a bit further in the text. Since these are literature values (I assume, since you don't have any data for this), instead of presenting a table, just describe this in one sentence. 

Table 3 - put reference to the guidelines in the caption of the table

LN249 - ...attention needs to be paid to toxicity...

Figure 1 and 2 - I would put these figures next to each other, and mark them with A) and B). This will ensure they don't split them in publication process.

Generally, Results section is still very messy and not clear. Firstly, presentation of values in Table 4 doesn't make sense. Why is it important to show inflow concentration of nutrients for every class? Isn't outflow more important? And if this is outflow, I am pretty sure that in order to reach Class A, TN is going to be lower than 7.8 mg/L (while not in guidelines, it is as a consequence of other treatment methods). Also if a number is in millions, no one cares about single digits; i.e. your water quantity should be in ML or GL. Also, not very important part of the table, since it's not varying across your analysis. Fix the units for other things too. Same for Table 5. 

But other than units, the whole message of the Results section doesn't make sense. E.g. Ln 352-354 - This was never part of the analysis. This is a method assumption, so why are you presenting it as a result? Same with 344-346, this is a method assumption from Table 3, why are you giving it again here. 

These are only some of the examples, but the whole Results section needs to be reconsidered and restructured with a clear aim in mind. At the moment, I find this work more useful as an incomplete literature review, rather than a novel research. 

Author Response

Point-by-point responses are provided in the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

All comments have been addressed and all the relevant modifications have been made to the manuscript which make it publishable in its present form.

Author Response

Point-by-point responses are provided in the attachment

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

I would like to thank authors for revising the manuscript. I think that GHG part is covered well now, but to make this work even better, it would be good to include similar breakdown for energy, both in Methods (describing calculations a bit clearer) and in the results (showing breakdown of different energy consumptions across all processes calculated). 

Author Response

Point-by-point response to the reviewer’s comments are reported in the attachment

Author Response File: Author Response.docx