Comparative Gate-to-Gate Life Cycle Assessment for the Alkali and Acid Pre-Treatment Step in the Chemical Recycling of Waste Cotton

Round 1

Reviewer 1 Report

The aim of this paper is of interest but the authors need to improve some aspects:

Section 1. Introduction: Authors have prepared a comprehensive presentation of the state of the art incorporating a sufficient number of scientific papers and summarizing the conclusions they have reached. As a recommendation, the authors could add more specifically the reasons or novel points that have led to the choice of the two alternatives employed. Similarly, it would be advisable for them to argue what the limitation of the gate-to-gate system consists of, so that readers understand that only the processes that occur within production will be evaluated and not those related to other phases such as extraction of raw materials, transport, use, etc.

Section 2. Material and methods: Authors explain, in a logical and precise way, all the key aspects that every LCA must have, showing fundamental information such as the objective, the scope, the functional unit or the limits of the system that they have taken into account for the analysis. The choice of calculation methodology is a key aspect to be taken into account, so it would be advisable for the authors to argue more deeply the reasons or grounds for their choice taken from the guide (Renouf, 2018).

Section 3. Results: As in the previous section, all the information is clearly and progressively detailed. It is advisable to move forward in the reading without getting lost even if the user is not an expert in the topics specifically covered or in life cycle analysis in general. In order to make a recommendation, what has happened in the MAETP impact category is a fact that globally affects many studies. In fact, there are specific articles that investigate the reasons. Nothing to mention with regard to this section.

Section 4. Conclusions: Although an attempt has been made to keep the conclusions light and to the point, I have the feeling that they are too short. I would recommend including a little more information in the paragraph to complete the study. It is curious that the sulphuric acid process is more environmentally sustainable than the one it is compared to. The process of neutralization of the waste water is a very important step in this aspect, it would be advisable to incorporate more information about this process, even if it is in a theoretical or summarized way.

References: The references used are sufficient and have a representative number of current references from the last 3 years.

In general, I find the document very complete and very well constructed. My congratulations to the authors for their paper.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors,

I found the manuscript well-written. The LCA sufficiently showed the contrast of environmental impact between the alkali and acid treatments. Congrats for the nice work.

I do not have much comment to improve. 

There are two main factors affecting the LCA: electricity consumption and material consumption. 

Electricity. Caption in Fig1. is nice. It concisely shows the likely outcome of electricity, where 1 hour vs 15 hours at the respective temperature. These measurements of electricity were based on actual bench-scale lab devices, right? Which are likely lead to an overestimation in prospective industry usage. A line or two clarifying this point will be nice. Probably somewhere around line 394, where you mentioned the theoretical net-zero-emission. 

Material. I appreciate the analysis of material contribution without electricity, line 391 onwards. I suggest to separate the paragraph into 3.5 sub-section instead of combining them with normalization. The message from normalization is: only those few impact indicators are significant, and the additional analysis without electricity is: material-wise alkali did consume more, and the impact of the chemicals are higher.

(Also, somehow the MDPI reviewer system does not provide me with the supplementary document (ESI)). 

Best regards,

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf