Study on Carbon Emissions from an Urban Water System Based on a Life Cycle Assessment: A Case Study of a Typical Multi-Water County in China’s River Network Plain

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

Title：Study on Carbon Footprint of Urban Water System Based on the Life Cycle Assessment: A Case Study of a Typical Multi-Water County in China's River Network Plain

 

In this manuscript, the authors constructed a carbon accounting framework for the Life Cycle Assessment of urban water systems and analyzed the carbon emission reduction potential of the water system under different scenarios. The study has implications for carbon emission reduction. But there are some issues needed to be cleared. Thus, I suggest that major revision is necessary before considering the acceptance.

 

1.      What is the current situation of carbon emissions from urban water systems. What is the basis for the cases selected for analysis in the manuscript and how representative is it?

 

2.      The authors said that the main sources of carbon emissions during the construction phase include material consumption, transportation consumption and construction consumption. The formula for calculating carbon emissions at this stage is also based on this classification. However, the data in the graphs used for the analysis show that based on intake, supply, drainage and reuse. What is the correspondence of data between different classifications. Similarly, the authors should explain the same issues in the operation phase and the demolition phase.

 

3.      The authors said this study averages the total lifecycle carbon emissions of each water engineering and facility over an annual scale. However, in the subsequent projections of total carbon emissions in 2030, whether the actual condition of water engineering and facility is taken into account. For example, which stage of the total lifecycle of the water engineering and facility are they in, and on the basis of this, the results obtained from the average data will be revised to obtain a more realistic projection.

 

4.      The authors analyzed the potential for carbon reduction under three different modes of operation. The authors should indicate which segments of the urban water system have a stronger potential for carbon reduction.

 

5.      The authors said “assuming further improvement in water resource utilization efficiency of urban water systems in the study area or the strengthening of constraints on related water resource development and utilization policy planning” could achieve the high low-carbon scenario. Based on the current state of the technology and water resource utilization efficiency of urban water systems, how much should the relevant indicators be increased to reach the scenario.

 

Comments on the Quality of English Language

Some sentences could be more concise and clear

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The present manuscript entitled “Study on Carbon Footprint of Urban Water System Based on the Life Cycle Assessment: A Case Study of a Typical Multi-Water County in China's River Network Plain” have the authors analyzes the "water-carbon" correlation mechanism of urban water systems, and constructs a carbon accounting framework for the Life Cycle Assessment of urban water systems. The results show that the operational phase is the main contributor to the carbon emissions of the urban water system in the research area, accounting for approximately 86% of the total carbon emissions. Among them, the supply and drainage links have the largest carbon emissions, accounting for 39% and 31% of the total carbon emissions, respectively. In terms of carbon emission intensity, the carbon footprint of the water cycling process using reclaimed water as the water source is higher than that of high-quality water and conventional water sources. The paper is encouraging and more precisely fits into the Journal. Before the manuscript deems acceptable for publication, it needs be revised very well. Some specific suggestions are listed below.

1. Authors must define clearly the novelty of your research paper compared to other similar works.

2. Introduction is somewhat monotonous and can be improved using the relevant recent literature.

3. Need to more discuss future perspectives related research work.

4. The authors must be rechecking the English of the manuscript. It is fairly poor in some parts of the paper and must improve it.

Comments on the Quality of English Language

It is necessary to refine the English language.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Recommendation: Major Revision

 

Comments to the Author

The topic of the manuscript is appropriately suited for publication. The manuscript is in general well written and organized. It provides a large amount of experimental data, and the work seems to be carefully executed. The authors used appropriate methods to address the aims and objectives of the study. The results obtained are also interesting and relevant. Overall, the study is technically solid and includes appropriate methods as well as pertinent results. However, and for the sake of full impact only, the authors are invited to consider the following list of suggestions and recommendations.

The reviewer has some specific comments/suggestions provided below.

Section (1 Introduction):

 

·         The mention of a "typical county in China" is quite general. For better comprehension, it would be beneficial to include specific details about the study area, such as its location, size, or particular characteristics that justify the choice of this region. Adding some specific details about the region, such as its geographic, demographic, or industrial features that make it representative or relevant to the study, would enhance understanding.

·         There is a slight redundancy in emphasizing the importance of understanding the relationship between water cycle processes and carbon emissions. To reduce redundancy, rephrase the sentence to maintain clarity while avoiding the repetition of ideas. Striking a balance between emphasizing importance and conciseness would be ideal.

Section (2.Methods) :

·         The "Methods" section is detailed, which is positive, but some parts could be presented more clearly. Divide the text into well-defined subsections with distinct titles for each step of the process (construction, operation, demolition). This will make the reading smoother and facilitate reference.

·         When discussing specific processes, such as the construction of pumping stations or wastewater treatment, include concrete examples to illustrate your points. Integrate specific examples of construction projects or wastewater treatment processes to bring your description to life. This will help the reader better understand the real-world applications of your methods.

·         Some calculations are described in general terms, but it would be useful to include numerical data to illustrate your calculations and results. Where possible, add quantitative data, such as energy consumption figures, specific carbon emissions, or volumes of treated water. This will strengthen the credibility of your results.

·         You mentioned the operational lifespan of different facilities but did not discuss how this influences the calculation of carbon emissions. Explain how you have taken the operational lifespan into account in the calculation of carbon emissions, especially when mentioning significant differences in the lifespans of different facilities.

Section (3. Results) :

·         Some sentences are quite complex and might benefit from simplification for better readability. For instance, in the sentence "The carbon emission intensities during the construction, operation, and decommissioning phases of the high-quality water subsystem are 0.08、0.90 and 0.05CO2eq/m3," it would be clearer with consistent spacing: "The carbon emission intensities during the construction, operation, and decommissioning phases of the high-quality water subsystem are 0.08, 0.90, and 0.05 CO2eq/m3."

·         Consider including a brief discussion on how your findings compare with existing literature or other relevant studies in the field. This can provide context and enhance the significance of your results.

·         Provide more interpretation of the results. Why are certain phases or subsystems showing higher carbon emissions? What are the implications of these findings?

·         Be precise in language. For instance, "The carbon emissions during the construction and demolition phases are 1.92×10 4 tons and 1.03×10 4 tons, respectively." It would be clearer to say, "The carbon emissions during the construction phase are 1.92×10 4 tons, and during the demolition phase, they are 1.03×10 4 tons."

·         Ensure a smooth flow between sentences and paragraphs, especially when transitioning between different aspects of the analysis. This aids in maintaining the reader's engagement..

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

In connection with the inevitably looming global problem of water shortages, issues of rational water use are acute, among which the solution to the issue of water recycling occupies a significant place. At the same time, when addressing issues of rational water use, which is most acute in urban areas, it is necessary to maintain energy efficiency, in particular, reducing the carbon footprint arising from energy production. On the one hand, these are two mutually exclusive tasks, on the other, it is necessary to achieve an optimal balance when solving these problems. The solution to this problem is complex, requiring comprehensive consideration of a large number of parameters, especially in relation to the conditions of large urban areas. The literature presents in some detail the results of studies on rational water use, but in private conditions, without taking into account a large number of features. The present work exploring the "water-carbon" correlation characteristics and carbon emission intensity under different water sources, and analyzing the carbon emission reduction potential of the water system in urban territory under different scenarios, utilizing statistical data, fills this gap. There are several new and interesting findings, for instance, construction of a model and methodology for assessing the carbon footprint of urban water systems throughout their lifecycle, from cradle to grave, at temporal and spatial scales, as well as the factors influencing carbon emissions in urban water systems are identified. The research allowed to determine the quantitative value that the operational phase of urban water systems is the main contributor to carbon emissions, accounting for 86% of the total carbon emissions throughout the lifecycle, as well as the effect of different stages upon the amount of carbon footprint.

The strength of the work: The convincing models built on comprehensive statistical analysis with account of variety of parameters. High applied relevance of the results obtained for the sustainable development of urban areas.

The weakness: The work would gain if the specificity of the certain different urban areas in China, as well as other countries were analyzed.

In general, the manuscript is scientifically sound with the appropriate design to address the issues under consideration. It is clear, relevant for the field and presented in a well-structured manner. The manuscript provides sufficient details that support the conclusions. It encompasses a vast amount of relevant case studies. The manuscript is suitable for publication in Sustainability in its present form.

Author Response

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Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

This article focuses on the carbon footprint of urban water system based on life cycle assessment, using a case study of a typical county with multiple water sources in the plain of China's river network. It investigates the correlation mechanism between the urban water cycle and carbon emissions and constructs a carbon accounting framework for the urban water system.

The article shows that the operational phase is the main contributor to carbon emissions from the urban water system in the research area, accounting for around 86% of total carbon emissions. Among them, the supply and drainage links have the highest carbon emissions, representing 39% and 31% of total carbon emissions, respectively.

The article also presents three scenarios to predict carbon emissions from the urban water system in 2030, based on different patterns of water supply and use, energy efficiency and planning policies.

The article suggests that for the coordinated development of “water saving and carbon reduction” in urban areas, future efforts should focus on improving the reuse rate of recycled water in urban life and industry, reducing the leakage rate of water distribution networks, and improve water treatment processes. These measures aim to increase water efficiency in urban water systems and reduce carbon emissions.

I had a great interest and pleasure in reading this first version of the article, may the authors be thanked and encouraged.

I give this article a favorable opinion.

Author Response

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Author Response File: Author Response.pdf

Reviewer 6 Report

Comments and Suggestions for Authors

The majority of the content in Section 2.1 appears to be inappropriate for the methods section. Figure 1 also seems unrelated to the methods, and this image does not present a new claim by the authors. I don't understand its significance in the context of research methods. What I see in this section looks more like an introduction to the current progress in wastewater treatment rather than a description of your research methods.

 

Section 2.2 also seems less relevant to the methods, with much of the content still introducing common knowledge. I hope you can succinctly outline in the research methods section what methods you used, the research process, rather than attempting to educate readers on management knowledge.

 

You should add a literature review section to provide detailed explanations of proprietary terms mentioned in the paper, such as life cycle theory, process analysis, and emission factor methods. Explain how they are defined, used, and the basis for their application.

 

Additionally, the rationale for the deductive reasoning in the paper is somewhat unclear. The formulation of some formulas seems subjective, and you need to provide stronger evidence or references.

 

Separate the results and discussion sections into independent chapters rather than combining data and personal opinions in a generalized manner throughout the text.

 

Try adopting a more reflective writing style to discuss the significance and contribution of the data, rather than merely restating the results descriptively.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have answered and addressed the major questions. I recommend to accept the current version.

Reviewer 3 Report

Comments and Suggestions for Authors

 Accept in present form

Reviewer 6 Report

Comments and Suggestions for Authors

I don't have any other comments.