Comparative Life Cycle Assessment Study on Carbon Footprint of Water Treatment Plants: Case Study of Indonesia and Taiwan
, Allen H. Hu 1,*, Chien-Hung Kuo 1 and Hongwei (Lance) Huang 1
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsSome justification and suggestions are as follows:
1. Comparison of LCA study on the Carbon Footprints of WTP in Indonesia and Taiwan is quite difficult as both countries are vastly different in their WTP technology. The rationale for choosing the location should be included and justified.
2. Figure 9-11 should be presented in one figure for easy comparison and bar graph would be more appropriate. The same goes for Figure 2-7.
Comments on the Quality of English Language
The manuscript should be thoroughly check for grammatical mistakes.
Author Response
1) Comparison of LCA study on the Carbon Footprints of WTP in Indonesia and Taiwan is quite difficult as both countries are vastly different in their WTP technology. The rationale for choosing the location be included and justified.
Author's comment: Highlighted
Author's answer: Thank you for your thoughtful suggestion. The rationale for choosing these locations lies in exploring novel solutions to improving the sustainability of the WTPs, especially in Indonesia. In our study; Taiwanese WTPs are somehow considered as a witness case. Therefore, in our study, we aim to evaluate how far Indonesian WTPs are from the Taiwanese WTPs in terms of sustainability. It has been highlighted in section 3.2 Goal and Scope; page 6; lines 562 – 567.
2) Figure 9-11 should be presented in one figure for easy comparison and bar graph would be more appropriate. The same goes for Figure 2-7.
Author's comment: Revised.
Author's answer: In this updated version, we reduce the number of water treatment plants (WTPs). Also, figures have been presented using bar graph as recommended by the reviewer. Figure 2, page 10 aims to show the total carbon footprint generation of the studied WTPs. From that figure, we can identify that Taiwanese WTPs are more ecologically friendly compared to those in Indonesia. From Figure 3-9; we would like to highlight the contribution of each element to the carbon footprint generation. The biggest contributor is the electricity consumed during the raw water intake phase. This information can be obtained from page 8 lines 841 – 853. In final the quality of the different figures has been improved.
3. The language has been improved.
Reviewer 2 Report
Comments and Suggestions for Authors
Authors used life cycle assessment method to trace the carbon footprints of 10 water treatment plants across Indonesia and Taiwan. This manuscript looks like still a draft to me, contextual redundancy and not well summarized concepts make readers very difficult to follow the flow of the manuscript. Some detailed issues are as follows:
1. Introduction and the Literature Review need to be merged and summarized well as a research article.
2. Authors need to provide citation/reference as soon as mentioning an accurate number, eg. line 53-54, line 56-57, line 268-269, line 286 (ISO 14067 is not even cited as the method) etc.
3. Table 2.1 is a blank table, clarification needed
4. line 306, authors mentioned some data may not be original, those referenced data need to be explicitly and clearly noted in the context.
5. section 4.1, it is very difficult to compare the CFA from different cities by the pie chart, since the category of different cites are different (variables and parameters are different in each case), nothing is comparable except the overall CF.
6. section 4.3, I am very confused with those charts, what are the the purple and grayish bars (the legends in the histogram and the label below don't match)? Multiple labels having the same name are also confusing. And those two have negative impact in ecosystems but positive on resources (Figure 13) ?
Comments on the Quality of English Language
English needs some polish to be concise and intelligible.
Author Response
Comment 1: Introduction and the literature Review need to be merged and summarized well as a research article.
Author's Response: Amended
Author's comment: Thank you for your thoughtful suggestion. The structure of the paper has been improved and we believe that with this structure it will be better to have an introduction. Therefore, we did not merge it with the literature review. One thing is sure, this comment helped us to improve the structure of the introduction and help us organize the literature review
Reviewer's comment 2: Authors need to provide citation/reference as soon as mentioning an accurate number, e.g. line 53-54; line 56-57; line 268-269, line 286 (ISO 14067 is not even cited as the method) etc
Author's Response: Revised
Author's comment:
The corrected version is as follow:
Line 40 – 42: The drinking water facility company PDAM of Indonesia is the principal supplier of clean water with a production capacity of 153,881 L/s, which meets around 19 – 20% of the country’s basic needs……Permana, A. (2020) [5].
This information is obtained from the yearly statistical note of the company managing water-related issues in Taiwan. Although it is evident that, these sectors are consuming more water, we believe that it is still necessary to highlight them in a general way. Line 42 – 45: According to the TWC statistical book published in 2020, the total water consumption in Taiwan mostly comes from agriculture, industrial, and domestic sectors.
Line 406 – 410: The Qingtian Dam, which supplies raw water to the Changxing and Gongguan purification plants, has a daily capacity of 1.08 million m3 of raw water, while the Zhitan Dam, serving only the Zhitan
water treatment plant, has a daily capacity of 2.70 million m3 of raw water (Taipei Water department) [39]. We are not sure if we get this highlight but we tried to rewrite our sentence as you can find below:
Page 7; Line 493 - 494: ISO 14067 was used as the method to quantify the carbon footprint while, ISO 14040, and ISO 14044 were employed as guidelines for the LCA method to calculate the CF in this study.
Reviewer's comment 3: Table 2.1 is a blank table, clarification needed.
Author's Answer: Table 2.1 is not blank. This table shows the operational units of the different WTPs. It aims to present the different technologies used in these countries. It can be found on page 7. Moreover, we have improved the quality of this table making it more captive.
Reviewer's comment 4:
Line 306, authors mentioned some data may not be original, those referenced data need to be explicitly and clearly noted in the context.
Author's comment: Amended.
Author's answer: Page 7; Line 511 – 517. The data were collected from the companies’ inventories and annual Corporate Social Responsibility (CSR) books. The electricity coefficient for GHG emission characterization is based on 2020 data reflecting each country’s overall GHG emissions. Based on data from the National Energy Administration of both countries, the average GHG emissions coefficient used for electricity was 0.848 kgCO2eq/kWh for Indonesia and 0.574 kg CO2eq/kWh for Taiwan respectively [40, 41]. The details on inventories of all the WTPs can be found in Tables 5, 6, 7, and 8, respectively, for Karang Pilang II, Karang Pilang III, Changxing, and Gongguan WTP in the supplementary materials. All the data about electricity GHG emission coefficient were obtained from the energy departments of the different countries.
Reviewer's comment 5:
Section 4.1, it is very difficult to compare the CFA from different cities by the pie chart, since the category of different city are different (variables and parameters are different in each case), nothing is comparable except the overall CF.
Author's comment: Explained.
Explained text: The goal of this study is to compare the CF emitted by these WTPs in these countries and see how far the least sustainable are from the most sustainable one. The same functional unit has been used. Although we acknowledge that several variables and parameters may influence the CF amount we still wish to analyze and compare to see how the technologies used may influence the CF emission. We believe that with the results of this study, Indonesian policy-makers in that field could learn from their counterpart in Taiwan. Moreover, bar graphs have been used to display the overall results.
Reviewer's comment 6: Section 4.3, I am very confused with those charts, what are the the purple and grayish bars (the legends in the histogram and the label below don't match)? Multiple labels having the same name are also confusing. And those two have negative impact in ecosystems but positive on resources (Figure 13) ?
Author's answer: Amended.
Revised text: The result is written in one section. The different graphs have been updated. We use bar graph to display the results. Yes, the WTPs in Taiwan have the least impact on resources and Human health but cause more damage to the ecosystem. This could be explained by the fact that these WTPs are employing more chemicals to improve the water quality which is not the case in Indonesia. The water quality in these two countries is different. Also, sometimes the chemical usage depends on the volume of water to treat. This information can be found on Page 13. In the ecosystem impact category, Taiwanese water treatment plants (WTPs) exhibited a more significant contribution compared to Indonesian WTPs, as shown in Figure 8. This discrepancy is primarily due to the substantial quantities of chemicals utilized during the treatment process in Taiwan. Chemicals are the second most significant environmental hotspot in water treatment, with Taiwanese WTPs deploying extensive amounts known to be toxic to ecosystem services. The volume of chemicals used is somewhat influenced by stringent water quality regulations.
Reviewer's comment 7: English needs some polish to be concise and intelligible.
Author's Answer: Yes, we agree. The language level has been improved.
Reviewer 3 Report
Comments and Suggestions for Authors
The paper addresses an exceptionally interesting and highly relevant issue. Although after reading the initial part of the paper, I expected an excellently structured and conceived scientific work, the main body of the paper lacks data for potential replication and verification of the obtained results. The reader and reviewer simply have to trust the authors' word that the applied LCA models are correctly set up. Detailed data on inputs/outputs with accurate specifications of individual quantities at each of the analyzed WTPs are simply missing, thus preventing the verification of the obtained results. Therefore, the main criticism is that the paper necessarily needs to be supplemented in this part, in order to contain all the necessary data for replication and verification of the obtained results. In the present form, the methodology and model settings themselves are untrustworthy.
Following are specific comments on individual parts of the paper:
1. All abbreviations should be defined upon their first appearance in the main body of the paper (excluding the abstract), including: CF, GHG, IPCC, etc.
2. When writing specific references that begin sentences or similar (e.g., ref. [4]), the names of the authors should be included, rather than starting the sentence with just the reference number. For example, 'Sala-Garrido et al. [4] found...'. The same applies to numerous other citations, for instance, references: 20, 21, 22, 23, 24, 25, 27, 28, etc.
3. Page 2/23, line 46: is there missing “kg” in the unit so there should be “0,95 kg CO2e/m3”. Also to what example (location/WTP) this data refers to? Or this is maybe some worldwide average? But it needs to be specified on what this amount refers to.
4. Page 2/23, line 51: I guess the should be “Nationwide” instead of “Worldwide”.
5. Page 2/23, line 53: stated amount of 153,88 l/s seems far to small (especially when later stated WWTP capacities are considered). Please check and correct. Also, the SI unit is “L/s”, not “L/ second”.
6. Page 3/23, lines 99-100: Maybe bacteria should be supplemented with “microbiological contamination”, and I believe chemical contaminants/pollutants should also be separately mentioned here.
7. Page 3, line 125: missing reference at the end of this section!
8. Subsection 2.3 doesn’t fit under the section “Literature review”. This should be moved later and merged with the section “Study Area”, especially since it pertains to the same subject, and some information is repeated.
9. Table 2.1 appears confusing due to the use of '0'. It is recommended to use labels such as 'YES/NO' or '+/-' or similar.
10. Page 4/23: The data for Mojokerto City WTP and Taipei City WTPs are incomplete: provide current capacities, especially more precise data for each of the Taipei WTPs being analyzed, instead of providing unnecessary information at the level of the entire Taiwan.
11. Page 5/23, lines 217-220: In recent years, trends also indicate the significant possibility of even stronger global warming than indicated. While these data are official, they primarily stem from sources and predictions that are several years old. Therefore, it would be advisable to provide at least a note acknowledging that with the adoption of trends that have been even more pronounced in recent years, even more significant warming than stated can be expected.
12. Use subscript where applicable: CO2, N2O, CH4, etc.
13. Page 7/23, lines 278-279: author refer to “CF of the urban water supply system”. Is this really the case, or the analysis (as I understood) in this paper are limited on WTP only. Urban water supply systems also encompass other elements, as pumping stations etc. that can also contribute significantly to the overall water supply system CF.
14. Page 7/23, authors state: “This study did not include the 288 sludge treatment process because some WTPs could not provide sludge treatment data.” This should be further emphasized and explained how this important item is leftout from the analysis and how can we still expect the results to be comparable. This can also be considered as the main shortcoming of the methodology of the study itself, so this fact should be further elaborated. Here, the importance of supplementing the study in accordance with the main comment is evident because it is not clear what exactly and in what quantities is included in the LCA model for each WTP.
15. Page 8/23, lines 314-315: This directly follows from comment number 14, and I believe this statement is incorrect based on what I understood from the paper. The study is based on the individual WTPs, not the entire water supply systems. Therefore, this needs further clarification!
16. Page 8/23_ authors state that “Chemical transportation to the treatment plant is not included.” I believe we can say that this is negligible, so it's not even included within the model boundaries?
17. Page 8/23 - The author's final remark regarding the shortcomings of the methodology and model is unnecessary. Indeed, it has been quite some time since the travel restrictions due to the pandemic, and online data collection in this case is entirely appropriate.
18. The scientific paper is typically written in the third-person passive voice. Therefore, it should not include phrases like 'our study,' 'we consider,' “we conducted”, etc.
19. Page 8/23, line 341: Sentence “In this process, The chemicals used in this WTP are polyaluminum…” needs to be rephrased.
20. Page 8/23, line 345: unit with number 0.276 is incomplete I guess? I guess this is per m3 of water purified.
21. Which units are used for the numbers provided in Figures 2-11? As they are, these graphs don't convey any meaningful information. Additionally, if a representation is given through pie charts, it's common to include the percentages of each category (to provide insight into the whole, i.e., 100%). Moreover, on some of these graphs, it's unclear what each number represents; the shares are too small, and it's simply not clear which number corresponds to which category. Therefore, a different representation should be considered. For example, in Figure 10, it's absolutely unclear what the numbers at the bottom represent and what each category is. There are similar instances in other figures as well.
22. There are some parts in chapters 4.1.1, 4.1.2, and 4.1.3 that are repetitive and provide similar information already covered in chapters 2.3 and 3.1. This should be reorganized to avoid unnecessary repetition. Or somehow combine these chapters.
23. Page 12/23, line 393: Once again, we come back to this main drawback of the methodology and the inadequacy of the conducted analyses. Was this fact ultimately considered through the developed LCA models, i.e., was this environmental impact quantified? Because it is significant and should not be easily disregarded; otherwise, comparing the obtained results wouldn't make much sense. This is again mentioned in page 16/23 – lines 481-483. Still it is not clear is this impact included in the models or not.
24. Complete alignment of the subchapter titles in 4.3.1, 4.3.2, and 4.3.3 is necessary.
25. Page 13/23 – authors mention use of the sand as the filter media. Since the paper lacks information on all input and output variables of the created models, it is unclear whether the final disposal of waste generated here (sand that needs to be replaced after some time) has been considered as another environmental impact or not. Depending on the quantities of new sand required and the generated waste sand for disposal, these impacts could also be significant in some cases.
26. Page 14/23, line 435 – The statement using references [34, 35] is repetition from the page before.
27. Table 4.2 caption. I guess “in” would be more appropriate than “per”.
28. Table 4.2 – 2nd column – Please use the same number of decimal places for all WTPs.
29. Page 15/23 – line 456 – what does the stated result (0.1768) refer to? Is this the average value for all 10 analyzed WTPs, or? This needs to be specified.
30. All images 12-21 need to be adjusted in terms of display size and font size. As they are, they are unreadable and unclear. At the very least, the y-axis should be stretched and the font size in the legends should be increased. Additionally, it is necessary to use the same colors for individual items across different images to facilitate easier tracking and comparison of results.
Additionally, all these images are presented in percentages, making it impossible to compare the overall impacts of different WTPs directly. Only the shares of individual items in the total impact result of each WTP can be compared. Why is so, can this be presented more appropriately?
31. It is necessary to adjust the size of the table, text, and font to match the rest of the paper. Explain which units of measurement are used and what the 'unit' column represents. A number without an explicitly stated unit of measurement means nothing (e.g., what DALY means).
32. Statement “Each country has its regulations on water quality, but the comparison is performed according to the water quality required by each country.” in the Conclusions is redundant.
Author Response
Reviewer's comment 1: All abbreviations should be defined upon their first appearance in the main body of the paper (excluding the abstract), including: CF, GHG, IPCC, etc.
Author's reply and comment: Thoroughly revised; Thank you for your thoughtful suggestion; this comment has been considered and all the abbreviations have been explained upon their first appearance and highlighted in the manuscript.
Reviewer's comment 2: When writing specific references that begin sentences or similar (e.g., ref. [4]), the names of the authors should be included, rather than starting the sentence with just the reference number. For example, 'Sala-Garrido et al. [4] found...'. The same applies to numerous other citations, for instance, references: 20, 21, 22, 23, 24, 25, 27, 28, etc.
Author's answer: Thank you for the thoughtful suggestion. The reference at the beginning of sentences has been corrected and highlighted in the manuscript based on your suggestion.
Reviewer's comment 3: Page 2/23, line 46: is there missing “kg” in the unit so there should be “0.95 kg CO2e/m3”. Also to what example (location/WTP) this data refers to? Or this is maybe some worldwide average? But it needs to be specified on what this amount refers to.
Author's answer: Revised.
It is not a worldwide average data. This study was conducted in England. It has been corrected in the document as below;
At Line 74-77: In that sense, Sala-Garrido et al.[7] in England and Wales analyzed the environmental burden of WTPs and found that the CF per cubic meter of clean water delivered to the end users was 0.95 kg CO2eq/m3, as computed using LCA methodology Their study acknowledged that the cost to offset one kilogram of CO2 is £0.264. Moreover, their study highlights the need for new technologies and practices that minimize water treatment costs.
Reviewer's comment 4: Page 2/23, line 51: I guess it should be “Nationwide” instead of “Worldwide”
Author's Replies: revised based on your suggestion and more recent information has been used.
The updated text is as follows: Line 38 – 39; Worldwide, more than two billion still do not have access to proper sanitary facilities [4]
Reviewer's comment 5: Page 2/23, line 53: stated amount of 153,88 l/s seems far to small (especially when later stated WWTP capacities are considered). Please check and correct. Also, the SI unit is “L/s”, not “L/ second”.
Author's answer: Revised based on your suggestion.
The revised text is as follows: Line 40 – 42: The drinking water facility company PDAM of Indonesia is the principal supplier of clean water with a production capacity of 153,881 L/s, which meets around 19 – 20% of the country’s basic needs……Permana, A. (2020) [5].
Reviewer's comment 6: Page 3/23, lines 99-100: Maybe bacteria should be supplemented with “microbiological contamination”’ and I believe that chemical contaminants/pollutants should also be separately mentioned here.
Author's answer: Information added based on your suggestion.
The added text: Line 162 – 165; A water treatment facility eliminates odors, color, turbidity, bacteria with microbiological contaminants, chemical pollutants, and other pollutants. The turbidity of raw water entering a treatment facility is often produced by colloidal clay and silt particles.
Reviewer comment 7: Page 3, line 125: missing reference at the end of this section!
Author's Answer: Revised.
The revised text: Page 3 Line 190: Chlorine is the most commonly used substance in disinfection. It can destroy most biological contaminants through mechanisms such as breaking the cell wall, breaking through cell permeability, passing through protoplasm, inhibiting cell enzyme activity, and inhibiting cell production Marhaba, T. F et al [16].
Reviewer's comment 8: Subsection 2.3 doesn’t fit under the section “literature review”. This should be moved later and merged with the section “Study Area”, especially since it pertains to the same subject, and some information is repeated.
Author's answer: Agree. The section has been moved and combined with section 3.1 (study area) and can be found on pages 5 and 6.
Reviewer's comment 9: Table 2.1 appears confusing due to the use of '0'. It is recommended to use labels such as 'YES/NO' or '+/-' or similar.
Author's Answer: Agree. The table 2.1 has been update following the recommendation of the reviewer. The “Yes/No” label has been used.
Reviewer's comment 10: Page 4/23: The data for Mojokerto City WTP and Taipei City WTPs are incomplete: provide current capacities, especially more precise data for each of the Taipei WTPs being analyzed, instead of providing unnecessary information at the level of the entire Taiwan.
Author's Answer: Agree and revise. The actual study compares the CF emission of WTPs from Surabaya City and Taipei City. In total, four WTPs are considered: two (Karang Pilang II and Karang Pilang III) from Surabaya and two ( Changxing and Gongguan) from Taipei. Karang Pilang II and Karang Pilang III have a capacity of 2750L/s and 2400L/s respectively, on page 5 line 339, and page 6 line 400. Changxing and Gongguan have a daily capacity of 314,124.02 m3 and 237,186.91m3 respectively page 6; line 413. More information related to the inventories can be found in the supplementary material.
Reviewer's comment 11: Page 5/23, lines 217-220: In recent years, trends also indicate the significant possibility of even stronger global warming than indicated. While these data are official, they primarily stem from sources and predictions that are several years old. Therefore, it would be advisable to provide at least a note acknowledging that with the adoption of trends that have been even more pronounced in recent years, even more significant warming than stated can be expected.
Author's Answer: Ok, thank you for your suggestions. This part has been updated. In the new manuscript, we added more recent information.
The added text: According to the UN Intergovernmental Panel on Climate Change (IPCC) latest synthesis report, human activities through the emission of greenhouse gases, have unequivocally caused global warming, with global surface temperature reaching 1.10C above 1800 – 1900 in 2011-2020. It has reduced food security and affected water security hindering efforts to meet the sustainable development goal. The different protocols and agreements such Kyoto Protocol and the Paris Agreement should be strengthened. To date, several countries have acknowledged the need to shift to a more sustainable economy and all sectors including the water treatment sector must contribute to the solution if governments are to keep their commitments.
Reviewer's comment 12: Use subscript where applicable: CO2 N2O CH4, etc.
Author's Answer: Yes, we agree and have corrected the mistakes about the manuscript writing error.
Reviewer's comment 13: Page 7/23, lines 278-279: author refer to “CF of the urban water supply system”. Is this really the case, or the analysis (as I understood) in this paper are limited on WTP only. Urban water supply systems also encompass other elements, as pumping stations etc. that can also contribute significantly to the overall water supply system CF.
Author's Answer: Agree. The new manuscript is more clear. This study aims to compute and compare the environmental impact of the CF emitted by the selected WTPs during clean water production through the LCA method. Raw water intake and the treatment process are the main targets including the chemicals used and the impact of waste emitted. In the system boundary, chemical transportation, waste treatment, and the distribution of clean water are excluded, as we did not conceive a treatment unit for that. System boundary page 7 section 3.2.
Reviewer's comment 14: Page 7/23, authors state: “This study did not include the 288 sludge treatment process because some WTPs could not provide sludge treatment data.” This should be further emphasized and explained how this important item is leftout from the analysis and how can we still expect the results to be comparable. This can also be considered as the main shortcoming of the methodology of the study itself, so this fact should be further elaborated. Here, the importance of supplementing the study in accordance with the main comment is evident because it is not clear what exactly and in what quantities is included in the LCA model for each WTP.
Author's Answer: Absolutely true. It is the main limitation of this study method as highlighted in page 7 lines 642 - 649. Our study boundary includes, the raw water supply and the treatment process including chemicals used and the impact of waste emitted. The system boundary start from raw water supply until the last step before clean water is delivered. The system boundary just considered the impact of the waste and sludge. We did not conceive a treatment unit for these wastes. We believe that our study will still have valuable insight because such a system boundary also allows us to determine the real impact of the chemicals and the electricity consumption during the treatment phase. This study will allow us to determine how much CF can be reduced if employing more advanced technologies like in Taiwan. The fact of not having a sludge treatment unit for Indonesian WTPs impacts the raw water quality, making these electrical machines consume more electricity to filter the water. The inventories can be found in the supplementary materials.
Reviewer's comment 15: Agree and revise. Yes, the system boundary of each WTP includes raw water abstraction until the last step before delivering clean water to the consumers. We aim to determine and compare the CF emitted during the treatment of water. It has been more emphasized on page 7 lines 489 - 501.
Reviewer's comment 16: Page 8/23_ authors state that “Chemical transportation to the treatment plant is not included.” I believe we can say that this is negligible, so it's not even included within the model boundaries?
Author's Answer: Ok.
Chemical transportation is not included in our system boundary. In this paper, we do not have any proof that this part can be negligible in the system boundary of the WTPs. The reason for excluding this segment from the system boundary is that we could not get information from all of the studied WTPs.
Reviewer's comment 18: The scientific paper is typically written in the third-person passive voice. Therefore, it should not include phrases like 'our study,' 'we consider,' “we conducted”, etc
Author's Answer: Yes We agree. It has been corrected to the best of our knowledge.
Reviewer's comment 19: Page 8/23, line 341: Sentence “In this process, The chemicals used in this WTP are polyaluminum…” needs to be rephrased.
Author's Answer: We agree with you. This section has been deleted since we are no longer studying Mojokerto WTP. In the actual revised document, we focus on WTPs including Karang Pilang II and III in Indonesia and Changxing and Gongguan in Taipei
Reviewer's comment 20: Page 8/23, line 345: unit with number 0.276 is incomplete I guess? I guess this is per m3 of water purified.
Author's Answer: Yes, we agree with your suggestion. The right unit is 0.276 kg CO2eq/m3. As we said, this section has been deleted.
Reviewer's comment 21: Which units are used for the numbers provided in Figures 2-11? As they are, these graphs don't convey any meaningful information. Additionally, if a representation is given through pie charts, it's common to include the percentages of each category (to provide insight into the whole, i.e., 100%). Moreover, on some of these graphs, it's unclear what each number represents; the shares are too small, and it's simply not clear which number corresponds to which category. Therefore, a different representation should be considered. For example, in Figure 10, it's absolutely unclear what the numbers at the bottom represent and what each category is. There are similar instances in other figures as well.
Author's Answer: The units used for the numbers are Kg/CO2 eq per Functional Unit (m3). Bar chart modeling is used to represent these figures in the updated version. They represent the Carbon Footprint contribution of each element (chemical consumption, electricity consumption, and impact of waste generated) employed during the water abstraction and treatment process. These graphs aim to highlight the most important source of CF in WTP. Through this result, we can easily identify the segment that needs to be improved to obtain a better outcome. In the previous version of the document, we aimed to highlight the share of each element, i.e., the contribution of electricity consumed during filtration, pumping, etc. But since the shares are very small in the actual version, we added all these values since they pertained to the same, i.e., electricity consumption. The overall results can be found in Figures 3 to 9 in Section 4.
Reviewer comment 22: There are some parts in chapters 4.1.1, 4.1.2, and 4.1.3 that are repetitive and provide similar information already covered in chapters 2.3 and 3.1. This should be reorganized to avoid unnecessary repetition. Or somehow combine these chapters.
Author's Answer: We agree. Thank you very much for your suggestion. Section 4 has been compiled in only one section to avoid redundancy. It can be found on page 8. The unnecessary information provided has been thoroughly addressed.
Reviewer's comment 23: Page 12/23, line 393: Once again, we come back to this main drawback of the methodology and the inadequacy of the conducted analyses. Was this fact ultimately considered through
Author's answer: The treatment of the waste and sludge generated during water treatment was not included in the system boundary. If considering the raw water and chemicals as inputs, our output includes clean water, sludge, and other waste. We evaluate the impact of these wastes. But we did not conceive a unit for treating them. In some WTPs, they have technology to treat the generated waste and sludge but in some of them, this technology is simply missing. So including this section in the system boundary will be unfair and will not convey real results.
Reviewer's comment 24: Complete alignment of the subchapter titles in 4.3.1, 4.3.2, and 4.3.3 is necessary.
Author's answer: We agree. This section has been merged to form one section. The results has been updated.
Reviewer's comment 25: Page 13/23 – authors mention use of the sand as the filter media. Since the paper lacks information on all input and output variables of the created models, it is unclear whether the final disposal of waste generated here (sand that needs to be replaced after some time) has been considered as another environmental impact or not. Depending on the quantities of new sand required and the generated waste sand for disposal, these impacts could also be significant in some cases.
Author's answer: In this study, some WTPs employ sand as filter media. In our results, when discussing wastes we are referring to sand and other generated waste. These wastes have been considered as environmental burdens, and their effect has been evaluated. The related information can be found in the supplementary material.
Reviewer's comment 26: Page 14/23, line 435 – The statement using references [34, 35] is repetition from the page before.
Author's response: This section has been deleted.
Reviewer's comment 27: Table 4.2 caption. I guess “in” would be more appropriate than “per”.
Author's response: We agree. it has been corrected. See page 9, line 835.
Reviewer's comment 28: Table 4.2 – 2nd column – Please use the same number of decimal places for all WTPs.
Author's answer: Yes we agree. it has been corrected. See page 9, table 2.
Reviewer's comment 29: Page 15/23 – line 456 – what does the stated result (0.1768) refer to? Is this the average value for all 10 analyzed WTPs, or? This needs to be specified.
Author's comment: It is not an average value; see page 8; lines 707 – 710. In previous studies, the average CF results from WTPs in Taiwan, as reported by Hu et al,. [31], were 0.1768 kg CO2eq/m3. These results are comparable to the actual study since the previous study includes infrastructure and distribution stages within their system boundary.
Reviewer's comment 30: All images 12-21 need to be adjusted in terms of display size and font size. As they are, they are unreadable and unclear. At the very least, the y-axis should be stretched and the font size in the legends should be increased. Additionally, it is necessary to use the same colors for individual items across different images to facilitate easier tracking and comparison of results. Additionally, all these images are presented in percentages, making it impossible to compare the overall impacts of different WTPs directly. Only the shares of individual items in the total impact result of each WTP can be compared. Why is so, can this be presented more appropriately?
Author's answer: Since the number of WTPs has been reduced, the number of graphs is also reduced. Moreover, bar graph design has been used to display the results. On the different bar graphs, we show the amount of CF generated by each element as requested. The figure can be found on pages 10 - 14; from Figure 2 to Figure 9. The quality of all the images has been improved. Thank you very much for your thoughtful suggestion.
Reviewer's comment 31: It is necessary to adjust the size of the table, text, and font to match the rest of the paper. Explain which units of measurement are used and what the 'unit' column represents. A number without an explicitly stated unit of measurement means nothing (e.g., what DALY means).
Author's comment: The size of all the tables has been addressed. On each figure, the unit is also mentioned. For example, the unit in analyzing the human health impact is DALY which means Disability-adjusted life year. The unit in resource is the 2013 USD. It indicates the amount of resources needed based on the value of the USD currency in 2013.
Reviewer's comment 32: Statement “Each country has its regulations on water quality, but the comparison is performed according to the water quality required by each country.” in the Conclusions is redundant.
Author's answer: Yes, we agree.
This part has been addressed and the conclusion has been well organized. See pages 15, lines 972 – 990
Reviewer 4 Report
Comments and Suggestions for AuthorsThe paper conducted a comparative study on the carbon footprints of ten water treatment plants in Indonesia and Taiwan based on the Life Cycle Assessment (LCA) methodology. The findings provide insights for the low-carbon transition of the aforementioned water treatment plants. However, the paper has several key issues that need to be addressed.
(1) The literature review is disorganized and lacks a clear logical structure. The comparative description of water treatment plants in Indonesia and Taiwan in section 2.3 should not be part of the literature review and might be more appropriately placed in the Materials or Methods.
(2) It is well known that the biggest challenge of the LCA model is the collection of baseline data. Even though the authors defined the scope of LCA accounting, there are significant differences in the actual construction and operation of different water treatment plants. How can the comparability and accuracy of data among the ten water treatment plants be ensured? The paper does not provide an explanation for this issue.
(3) Additionally, different LCA calculation platforms (such as Simapro and Gabi) may lead to varying results. The authors have not detailed the specific implementation process of the LCA, which requires further clarification. In studies on LCA topics, it is common practice to provide readers with key data and processing details as appendices.
(4) Should the section number "3.1 Research Limitations" be "3.4"? Additionally, the discussion of research limitations should be part of the discussion section rather than the methodology.
(5) According to the LCA accounting boundary defined in Figure 1 and the textual description in section 3.2, wastewater treatment is clearly not within the accounting scope of this study's carbon footprint. However, why are the carbon footprint calculation results for the wastewater treatment process frequently mentioned in the results analysis?
(6) The authors focus on electricity in terms of energy input. However, aside from the carbon footprint generated by electricity consumption, do these water treatment plants consume other types of energy (such as fossil fuels) during their operational cycles?
(7) The results and discussion section only provides a statistical description of the carbon footprint data for the ten water treatment plants, lacking an in-depth analysis of the potential causes. It does not truly achieve a comparative study of the process flows and operational modes among different water treatment plants.
(8) Electricity and chemical consumption are identified as the two major sources of the carbon footprint for water treatment plants, which is a primary conclusion of this study. However, this study mainly addresses the carbon footprints of the water extraction and water treatment stages, where the primary carbon sources are evidently electricity consumption and chemical input. From this perspective, the value and significance of the research results are not very apparent.
(9) The paper contains numerous detailed errors and lacks standardized expressions.
Comments on the Quality of English LanguageExtensive editing of English language required
Author Response
Reviewer's comment 1: The literature review is disorganized and lacks a clear logical structure. The comparative description of water treatment plants in Indonesia and Taiwan in section 2.3 should not be part of the literature review and might be more appropriately placed in the Materials or Methods
Author's answer: Amended. Thank you for your thoughtful comment. The structure of the literature review has been improved. The section 2.3 comparing the WTPs in Indonesia and Taiwan has been moved to section 3 materials and method; study area. The literature review follows a structure where we start by giving general information about the water supply system on pages 2&3; Water treatment process lines on page 3 lines 156 - 190; LCA of the Water Treatment Process and finally previous studies about Carbon footprint assessment. This is the logic we follow in the literature review.
Reviewer's comment 2: It is well known that the biggest challenge of the LCA model is the collection of baseline data. Even though the authors defined the scope of LCA accounting, there are significant differences in the actual construction and operation of different water treatment plants. How can the comparability and accuracy of data among the ten water treatment plants be ensured? The paper does not provide an explanation for this issue.
Author's explanation: As we highlighted in the document, this study aims to compare the CF emissions based on the functional unit. Many factors including the technology used, the materials, and the source of electricity can influence the CF value but in this study, we aim to show how CF can be generated in the actual state of these WTPs. In the updated version of the document, we compare four WTPs in these two countries. With these results, Indonesian policymakers can easily realize how much CF they could reduce if using the same technology as in Taiwan.
Reviewer's comment 3 : Additionally, different LCA calculation platforms (such as SimaPro and Gabi) may lead to varying results. The authors have not detailed the specific implementation process of the LCA, which requires further clarification. In studies on LCA topics, it is common practice to provide readers with key data and processing details as appendices.
Author's answer: Amended. We highlight that using different software may lead to different results. In this study, SimaPro has been used. The key inventories can be found in the supplementary materials.
Reviewer's comment 4: Should the section number "3.1 Research Limitations" be "3.4"? Additionally, the discussion of research limitations should be part of the discussion section rather than the methodology.
Author's answer: We agree. The research limitations have been merged in the discussion section.
Reviewer's comment 5: According to the LCA accounting boundary defined in Figure 1 and the textual description in section 3.2, wastewater treatment is clearly not within the accounting scope of this study's carbon footprint. However, why are the carbon footprint calculation results for the wastewater treatment process frequently mentioned in the results analysis?
Author's answer: We focus on electricity usage. These WTPs do not have the same source of electricity. Those in Indonesia are employing coal while in Taiwan, it is mostly crude oil. All the energy consumed is converted into electricity to facilitate the estimation.
Reviewer's comment 7: The results and discussion section only provides a statistical description of the carbon footprint data for the ten water treatment plants, lacking an in-depth analysis of the potential causes. It does not truly achieve a comparative study of the process flows and operational modes among different water treatment plants.
Author's answer: Amended.
Besides the statistical comparison, we identify the potential causes of the differences found in the results. First of all, the result is compiled in one section named Section 4. Results and discussion page 8; line 699 –901. The difference in electricity consumption is explained by the state of the different machines being used. In Indonesia, electrical machines used for water purification are very old thus increasing their consumption, also, the main source of electricity in Indonesia is coal while in Taiwan it is crude oil. Coal is known to be the dirtiest fuel because emitting much more greenhouse gasses than oil.
Reviewer's comment 8: Electricity and chemical consumption are identified as the two major sources of the carbon footprint for water treatment plants, which is a primary conclusion of this study. However, this study mainly addresses the carbon footprints of the water extraction and water treatment stages, where the primary carbon sources are evidently electricity consumption and chemical input. From this perspective, the value and significance of the research results are not very apparent.
Author's answer: Explained
The value of this study lies in the comparison made among the four WTPs. We identified that the primary sources of CF emission are electricity input and chemicals. By comparing these four WTPs, we aim to demonstrate how far Indonesian WTPs are from Taiwanese WTPs in terms of sustainability. Still, in Indonesia, this study can be considered as a guideline for improving WTP sustainability since they know now where to improve. Moreover, we were able to know how much CF can be cut down by using modern technologies and changing the source of electricity to at least oil which emits less CF compared to the actual source (coal). Taiwanese WTPs are considered champions in sustainability and Indonesian WTPs could learn from their technologies to cut down their emission to align with their challenge of achieving net zero by 2060 or even sooner.
Reviewer's comment 9: The paper contains numerous detailed errors and lacks standardized expressions.
Author's comment: To the best of our knowledge, we believe that we have addressed all the mistakes.
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsAll of my previous comments have been addressed by the authors, and most of them have been adequately adopted, which I believe has significantly improved the quality of the paper. Although there are still some aspects that could be improved if complete data on the functioning of all analyzed plants were available, I consider the paper, in its current form, to be of satisfactory quality for publication, as these potential shortcomings have now at least been acknowledged in the manuscript. I would, therefore, like to point out some minor technical issues: in many instances, "Kg" is used instead of "kg"; there are still several cases of incorrect notation of chemical formulas (not using subscripts), even in some graph titles, and in some graphs, there are also missing spaces between values and units. I advise that all of these issues be reviewed once again before the paper is published.
Author Response
Comments: All of my previous comments have been addressed by the authors, and most of them have been adequately adopted, which I believe has significantly improved the quality of the paper. Although there are still some aspects that could be improved if complete data on the functioning of all analyzed plants were available, I consider the paper, in its current form, to be of satisfactory quality for publication, as these potential shortcomings have now at least been acknowledged in the manuscript. I would, therefore, like to point out some minor technical issues: in many instances, "Kg" is used instead of "kg"; there are still several cases of incorrect notation of chemical formulas (not using subscripts), even in some graph titles, and in some graphs, there are also missing spaces between values and units. I advise that all of these issues be reviewed once again before the paper is published.
Response: Thank you very much for your helpful guidance. Regarding the complete data of these WTPs, the data used to conduct the LCA can be found in the appendix documents. In all the notation, kg has been used instead of Kg. Also, space has been considered between values and the units in all the notation i.e. 0.067 kg CO2eq/m3. Additionally, subscript has been used as shown in the following text. “Hydrolyzing metal salts, such as aluminum Al2(SO4)3.14H2O, ferric sulfate Fe2(SO4)3.9H2O, and ferric chloride FeCl3.6H2O”. Section 2.2. Second paragraph, lines 171 and 172.
Author Response File: 
Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsSome of the questions I mentioned last time have not been positively answered or actively modified.
Comments on the Quality of English LanguageSome of the questions I mentioned last time have not been positively answered or actively modified.
Author Response
Comment 1: Some of the questions I mentioned last time have not been positively answered or actively modified.
Response:
Thank you for your thoughtful comment. We have improved the answers provided last time. Thank you very much; we believe that all these comments have helped us to improve the quality of our manuscript.
First-Round Comments and Responses:
Comment 1: The literature review is disorganized and lacks a clear logical structure. The comparative description of water treatment plants in Indonesia and Taiwan in section 2.3 should not be part of the literature review and might be more appropriately placed in the Materials or Methods.
Response: Thank you for your thoughtful comment. The structure of the literature review has been improved. Section 2.3 comparing the WTPs in Indonesia and Taiwan has been moved to section 3 materials and Method; study area. The literature review follows a structure where we start by giving general information about the water supply system on pages 2&3; Water treatment process lines on page 3 lines 156 - 190; LCA of the Water Treatment Process and finally previous studies about Carbon footprint assessment. This is the logic we follow in the literature review.
Comment 2: It is well known that the biggest challenge of the LCA model is the collection of baseline data. Even though the authors defined the scope of LCA accounting, there are significant differences in the actual construction and operation of different water treatment plants. How can the comparability and accuracy of data among the ten water treatment plants be ensured? The paper does not provide an explanation for this issue.
Response: Thank you very much for this insightful remark. As we highlighted in the document, this study aims to compare the CF emissions based on one cubic meter of clean water ready for distribution. Many factors including the technology used, the distribution of clean water, and the source of electricity can influence the CF value but in this study, we aim to realize how ecologically friendly are the Taiwanese WTPs compared to the Indonesian ones. In the updated version of the document, we compare four WTPs in these two countries. With these results, Indonesian policymakers can easily realize how much CF they could reduce if using at least the same technology as in Taiwan. Indonesia is committed to achieving net zero earlier therefore requiring effort all sectors and policymakers are willing to learn from other counterparties to achieve this tremendous target.
Comment 3: Additionally, different LCA calculation platforms (such as SimaPro and Gabi) may lead to varying results. The authors have not detailed the specific implementation process of the LCA, which requires further clarification. In studies on LCA topics, it is common practice to provide readers with key data and processing details as appendices.
Response: We highlight that using different software may lead to different results. In this study, we employed SimaPro as the main software because we do not have access to others including Gabi to compare the results. However, we have mentioned that the results may vary based on the software employed; see section 2.3. The key inventories can be found in the supplementary materials associated with the new version.
Comment 4: Should the section number "3.1 Research Limitations" be "3.4"? Additionally, the discussion of research limitations should be part of the discussion section rather than the methodology.
Response: The research limitations have been moved to section 3.4 page 8; lines 576 – 583. Their impacts have been discussed in the results and discussions part.
Comment 5: According to the LCA accounting boundary defined in Figure 1 and the textual description in section 3.2, wastewater treatment is clearly not within the accounting scope of this study's carbon footprint. However, why are the carbon footprint calculation results for the wastewater treatment process frequently mentioned in the results analysis?
Response: Thank you very much for your comment. The sludge treatment unit is not in the scope of this study which is considered as a limitation of the actual results as the WTPs in Indonesia do not have these facilities. However, the impact of the waste generated has been included in our calculation. We did so since we would like to compare the total CF generated by WTPs in Taiwan and Indonesia. The differences in the results could be explained by the state of technologies used, the source of electricity, and the kind of chemicals used.
Comment 6: The authors focus on electricity in terms of energy input. However, aside from the carbon footprint generated by electricity consumption, do these water treatment plants consume other types of energy (such as fossil fuels) during their operational cycles.
Response: Thank you for your thoughtful comment. The main energy source of these WTPs is electricity. In our study, we did not include any other type of energy.
Comment 7: The results and discussion section only provides a statistical description of the carbon footprint data for the ten water treatment plants, lacking an in-depth analysis of the potential causes. It does not truly achieve a comparative study of the process flows and operational modes among different water treatment plants.
Response: We add some details explaining the comparability process of this study. Besides the statistical comparison, we identify the potential causes of the differences found in the results. First of all, the result is compiled in one section named Section 4. Results and discussion page 8; line 586 –954. The difference in electricity consumption is explained by the state of the different machines being used. In Indonesia, electrical machines used for water purification are very old thus increasing their electricity consumption, also, the main source of electricity in Indonesia is coal while in Taiwan it is crude oil. Coal is known to be the dirtiest fuel because emitting much more greenhouse gasses than oil. The difference in CF value is also due to the operational unit. Indonesian WTPs are using old techniques to purify water. Also, the raw water quality affects the functioning of the filters. In Indonesia, these filters are consuming much more electricity. See Table 1 page 6 and Results and Discussion part 8 first paragraph.
Comment 8: Electricity and chemical consumption are identified as the two major sources of the carbon footprint for water treatment plants, which is a primary conclusion of this study. However, this study mainly addresses the carbon footprints of the water extraction and water treatment stages, where the primary carbon sources are evidently electricity consumption and chemical input. From this perspective, the value and significance of the research results are not very apparent.
Response: The value of this study lies in the comparison made among the four WTPs. The objective of this study is to compare the CF emission among the four WTPs. By comparing these four WTPs, we aim to demonstrate how far Indonesian WTPs are from Taiwanese WTPs in terms of sustainability. Still, in Indonesia, this study can be considered as a guideline for improving WTP ecological sustainability since they know now where to improve. Moreover, we were able to know how much CF can be cut down by using modern technologies and changing the source of electricity to at least oil which emits less CF compared to the actual source (coal). Taiwanese WTPs are more eco-friendly. Indonesian WTPs could learn from Taiwanese WTPs to improve the state of their technologies to cut down their emission to align with their challenge of achieving net zero by 2060 or even sooner.
Author Response File: Author Response.pdf
