Augmentation of Reclaimed Water with Excess Urban Stormwater for Direct Potable Use
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsI have reviewed the paper entitled " Augmentation of Reclaimed Water with Excess Urban Stormwater for Direct Potable Use: A Holistic Approach to Sustainable Water Resources Management". In this paper, the authors tried to illustrate the potential of reclaimed water as a source of potable uses. The study is interesting and very updated, and the experiments were designed appropriately. The results and discussion are well-equipped with in-depth analysis. This paper can be published in the Sustainability journal with some minor modifications:
1. Please add some numerical results in the Abstract.
2. Hypothesis and novelty were not amended in the introduction. Revise accordingly.
3. Keywords can be revised. Some of the words used in the Title are used repeatedly in the Keywords section. Delete them.
4. How do authors could connect "circular economy" in this paper?
5. How do authors recover useful resources from the model?
6. What could be the energy management strategies in reclaimed water resources management?
7. Please assess the economic and technological viability of the design.
Comments on the Quality of English Language
Moderate English editing needed.
Author Response
- Please add some numerical results in the Abstract.
We appreciate this reviewer’s comment. We added the following sentence to state the concentrations of total dissolved solids and nitrate-N in Abstract.
Reclaimed water tends to have high concentrations of dissolved solids (>500 mg/L) and nitrate-N (>10 mg/L), which can be lowered by blending it with stormwater or rainwater.
- Hypothesis and novelty were not amended in the introduction. Revise accordingly.
This study is novel because the combination of stormwater and reclaimed water for potable reuse has not been explored as described at the end of second paragraph of Introduction. We reiterated this at the end of Introduction:
Original: This paper explores the feasibility, potential benefits, and challenges of blending excess urban stormwater with treated wastewater at AWPFs for potable reuse.
Revised: This paper explores the feasibility, potential benefits, and challenges of blending excess urban stormwater with treated wastewater at AWPFs for potable reuse, which is a novel concept.
We also added the following sentence to propose a hypothesis:
We hypothesize that this approach is conceptually feasible and enables the construction of AWPFs without RO by improving water quality and reducing salinity across diverse climate regions.
- Keywords can be revised. Some of the words used in the Title are used repeatedly in the Keywords section. Delete them.
We appreciate this author’s suggestion. The title has been shortened to avoid the wordiness. We have deleted the redundant keywords and added different ones as follows:
Original: Circular water, closed-loop, potable reuse, reclaimed water, stormwater, sustainable water supply, water reuse
Revised: Circular water, drinking water, treated wastewater, rainwater, sustainable water supply, water reuse
- How do authors could connect "circular economy" in this paper?
This is a good point. We would like to promote circularity and closed-loop water by using our concept, but this wasn’t very clear in our original manuscript. We have revised Sections 4.2 and 5 to clarify and elaborate this point.
Section 4.2
Original: It is also possibility to reuse the entire wastewater effluent and create a completely closed-loop water supply system, if enough stormwater is secured.
Revised: It is also possible to reuse the entire wastewater effluent and create a completely closed-loop, circular water supply system, if sufficient stormwater is secured to replace and eliminate surface water or groundwater withdrawals.
Section 5 Conclusions
Original: By using this innovative approach, a completely closed-loop water system with little/no environmental discharge of liquid waste can be achieved, which will support the sustainable development of our society, as well as the protection and preservation of the environment.
Revised: This innovative approach can achieve a completely closed-loop, circular water system with minimal or no water withdrawal and environmental discharge, supporting both sustainable development and environmental preservation.
- How do authors recover useful resources from the model?
We appreciate this reviewer’s comment. However, we are not proposing or constructing a model in this study. We believe that the most important resource to be recovered is water itself in our proposed approach, which handles primarily liquid phase of wastewater and stormwater.
- What could be the energy management strategies in reclaimed water resources management?
This is a very good question. We are going to investigate the energy requirements and more quantitative water quality and quantity predictions in the next project. We have added the following sentence to address this:
Further research is needed and currently underway to develop quantitative models that predict the quantity and quality of stormwater-reclaimed water blends at various locations and assess their techno-economic viability, including energy requirement and management.
- Please assess the economic and technological viability of the design.
Conceptually, this approach is technically feasible in terms of treatment technologies because the scheme shown in Figure 2 consists of existing technologies currently used at AWPFs. Economic feasibility and viability are still uncertain because of the availability of stormwater and their impact on water quality on a continuous basis. Again, we are currently pursuing a follow-up study to investigate this further. To affirm the technical feasibility of proposed scheme, the following sentence was added in Section 3.3:
All these unit processes have been used at conventional water treatment plants and AWPFs, and the construction and operation of a facility are technically feasible [7].
Reviewer 2 Report
Comments and Suggestions for AuthorsPaper "Augmentation of Reclaimed Water with Excess Urban Stormwater for Direct Potable Use: A Holistic Approach to Sustainable Water Resources Management" presents a topic related to the water management, in general.
Several suggestions will be emphasized:
- The title seems too long and contains too much information.
- Edit keywords. These should not be words from the title, but significant words from the abstract.
- This topic in water management - groundwater and surface water - is very current. This is precisely why I believe that the Introduction is not supported by a sufficiently large volume of previous research on the topic of water use, i.e. a sufficient number of references that consider similar methodology or examples from world practice.
- The Materials and Methods chapter does not contain a description of the applied methodology. Only the input parameters discussed further are shown.
- The schemes and concepts shown in the results may have more significance for the methodology.
- On the other hand, the discussion should be adjusted with the results obtained by the authors. It seems too general.
- A conclusion should not be the same as a summary. Here it should be written briefly why the paper is worth publishing ... This refers primarily to the scientific contribution of the research carried out, and also to the importance it has for the academic community and engineering practice.
Author Response
- The title seems too long and contains too much information.
We appreciate this author’s suggestion. The second part “A Holistic Approach to Sustainable Water Resources Management” has been removed from the title.
- Edit keywords. These should not be words from the title, but significant words from the abstract.
We appreciate this reviewer’s suggestion. We deleted the redundant keywords and added different ones as follows:
Original: Circular water, closed-loop, potable reuse, reclaimed water, stormwater, sustainable water supply, water reuse
Revised: Circular water, drinking water, treated wastewater, rainwater, sustainable water supply, water reuse
- This topic in water management - groundwater and surface water - is very current. This is precisely why I believe that the Introduction is not supported by a sufficiently large volume of previous research on the topic of water use, i.e. a sufficient number of references that consider similar methodology or examples from world practice.
We appreciate this reviewer’s comment. We have added several references (#1, #6, #8, and #9) on water reuse in Introduction as suggested.
- The Materials and Methods chapter does not contain a description of the applied methodology. Only the input parameters discussed further are shown.
We appreciate the reviewer’s comment. This study consists of three parts: a quantitative analysis of water quality, hypothetical and conceptual facility design, and a discussion on the applicability of the proposed approach under various conditions and scenarios. The Materials and Methods section details the sampling and analytical methods, as the conceptual facility design relies on a basic mass balance analysis and unit conversion. We believe that the latter two parts are straightforward as presented in Results (Section 3.3) and Discussion and do not require additional descriptions in Materials and Methods.
- The schemes and concepts shown in the results may have more significance for the methodology.
We appreciate this reviewer’s comment. Again, the conceptual design is based on a very simple mass balance and unit conversions and would not require extensive descriptions of how it was done. The process scheme shown in Figure 2 is a possible example using currently available treatment technologies widely used at conventional water treatment plants, as well as AWPFs. To highlight this point, an additional sentence has been added in Section 3.2:
All these unit processes have been used at conventional water treatment plants and AWPFs, and the construction and operation of a facility are technically feasible [7].
- On the other hand, the discussion should be adjusted with the results obtained by the authors. It seems too general.
The Discussion section aims to explore the applicability of the proposed approach (i.e., blending stormwater and reclaimed water for potable use/reuse) within a broader context, while the water quality analysis and conceptual design parts (the Results section) focus on a specific case study in Central Texas. As this is the first paper discussing this novel approach, we believe it is important to address some basic factors and preliminary aspects. Although the discussion may appear general and somewhat superficial, these initial considerations are crucial for assessing the techno-economic viability of the approach. We are currently conducting a follow-up study to provide a more detailed evaluation of viability, incorporating additional water analysis and quantitative models based on historical climate data. To illustrate this, we have added the following sentence at the end of Conclusions:
Further research is needed and currently underway to develop quantitative models that predict the quantity and quality of stormwater-reclaimed water blends at various locations and assess their techno-economic viability, including energy requirement and management.
Also, the likely favorable condition of Central Texas is highlighted in the Discussion section, as well as Conclusions.
- A conclusion should not be the same as a summary. Here it should be written briefly why the paper is worth publishing ... This refers primarily to the scientific contribution of the research carried out, and also to the importance it has for the academic community and engineering practice.
We appreciate this reviewer’s comment. We agree that Conclusions should be strengthened. We have thoroughly revised Conclusions as follows:
Original: Table 3 summarizes the pros and cons of the proposed approach to utilize stormwater and reclaimed and produce potable water in different types of communities and climates as discussed in the previous section. It is apparent that this holistic approach to supplement existing water resources such as groundwater and surface water with currently underutilized stormwater and reclaimed water can be widely applicable. This re-search paper highlighted the preliminary feasibility of this novel approach and provided guidelines for designing new stormwater collection and storage systems, as well as AWPFs. Since water quality and availability vary significantly, any design and implementation of new water infrastructure systems need to be carefully studied, planned and executed with site-specific considerations. By using this innovative approach, a completely closed-loop water system with little/no environmental discharge of liquid waste can be achieved, which will support the sustainable development of our society, as well as the protection and preservation of the environment.
Revised: This research paper evaluated and revealed the preliminary feasibility of the use of excess urban stormwater to augment reclaimed water for potable reuse for the first time. Conceptual guidelines for designing stormwater collection and storage systems, as well as AWPFs using a combination of existing advanced unit processes, are provided. This holistic approach to supplement existing water resources such as groundwater and surface water with currently underutilized stormwater and reclaimed water can be widely applicable (Table 3). Medium-size suburban communities, especially newly developed subdivisions, in a warm and semi-arid climate such as Central Texas appear to be the most promising location to implement the stormwater-reclaimed water blending for potable reuse. This innovative approach can achieve a completely closed-loop, circular water system with minimal or no water withdrawal and environmental discharge, supporting both sustainable development and environmental preservation. Since water quality and availability vary significantly, any design and implementation of new water infrastructure systems need to be carefully studied, planned and executed with site-specific considerations. Further research is needed and currently underway to develop quantitative models that predict the quantity and quality of stormwater-reclaimed water blends at various locations and assess their techno-economic viability, including energy requirement and management.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have made an effort to improve the quality of scientific paper. A few more suggestions will be added.
- As the authors stated that part of the methodology is in the results, it is not very acceptable for scientific work. In the chapter where the methodology is described, as I mentioned in the first report, the input parameters are given. It is not a scientific methodology. When researching water/groundwater, both field research and cabinet and laboratory research are of great importance. The values ​​of the measured parameters do not represent a methodological procedure!
- As I stated in the first report, it was necessary to pay attention to previous research and references (Introduction chapter). Why are there so many references in the results and discussion? In the Results and Discussion chapter, the core is for the authors to present their research ... Citing a large number of references is not very common ...
- The scheme shown in the figure in the results is more suitable for a chapter where the methodological procedure should be described in detail.
- The table in the conclusion is generally a presentation of the results. Here it is necessary to specify the state of the art of your research...
Author Response
The authors have made an effort to improve the quality of scientific paper. A few more suggestions will be added.
Response: We sincerely appreciate Reviewer 2 for the time and effort to review and improve this manuscript.
- As the authors stated that part of the methodology is in the results, it is not very acceptable for scientific work. In the chapter where the methodology is described, as I mentioned in the first report, the input parameters are given. It is not a scientific methodology. When researching water/groundwater, both field research and cabinet and laboratory research are of great importance. The values ​​of the measured parameters do not represent a methodological procedure!
Response: We appreciate the reviewer's feedback and acknowledge that the presentation of our methodology may be unconventional. Our intention in this scientific research article is to propose a novel approach for sustainable water resources management, which is based on a case study involving a hypothetical facility design followed by a broader discussion, rather than the traditional lab or field-based experimental research. However, we agree that providing a clear methodological framework is essential for readers. Therefore, we have added a detailed paragraph at the end of the Materials and Methods section as follows and removed the methodological descriptions from the Results section:
Based on the water quality data, a hypothetical one million gallons per day (1 MGD or 3,800 m3/d) system was designed using reclaimed water and stormwater without RO based on a mass balance approach to achieve finished purified water that meets the US EPA National Primary and Secondary Drinking Water Regulations. For example, to eliminate RO, it is eminent to reduce the total dissolved solids (TDS) concentration below 500 mg/L. The following equation was used to calculate the blend ratio:
[TDS (mg/L)]Reclaimed Water × (1 – x) + [TDS (mg/L)]Stormwater × x = 500 mg/L (1)
where [TDS (mg/L)]Reclaimed Water and [TDS (mg/L)]Stormwater are the average TDS concentration of reclaimed water and stormwater, respectively, and x is the proportion of stormwater to be added. Then, estimated concentration of water constituent A in blended water can be determined by the following equation:
[A (mg/L)]Reclaimed Water × (1 – x) + [A (mg/L)]Stormwater × x = [A (mg/L)]Blended Water (2)
This 1 MGD facility can support approximately 6,400 people assuming a per capita municipal water demand of 157 gallons (594 L) per day in Texas [24]. The average annual rainfall of 35.5 inches (902 mm) in Central Texas [25] was used to estimate the stormwater availability and impervious surface requirement. Stormwater storage capacity requirements were calculated based on the daily, weekly, monthly, and yearly stormwater requirements. Subsequently, an AWPF scheme was constructed based on the existing literature on contaminants of concerns, such as nitrate-N [26-28], color [29-32], PFAS [33-35], and sucralose [36-38]. Pathogenic microorganisms removal requirement was assessed based on the Texas Commission on Environmental Quality (TCEQ) guidelines [39] that requires a minimum of 8, 5.5, and 6 log removal of enteric viruses, Cryptosporidium oocysts, and Giardia cysts for DPR.
- As I stated in the first report, it was necessary to pay attention to previous research and references (Introduction chapter). Why are there so many references in the results and discussion? In the Results and Discussion chapter, the core is for the authors to present their research ... Citing a large number of references is not very common ...
Response: We appreciate the reviewer’s feedback on the use of references. Citation practices can vary significantly among different research areas. In many cases, it is not uncommon for 30-50% of the references to be cited within the Results and Discussion sections, as these sections often require references to support the interpretation of data and to contextualize findings within existing literature. However, we acknowledge the reviewer’s concern and have carefully reviewed the references in our manuscript. As a result, we have moved some references from the Results and Discussion sections to earlier sections. In the revised manuscript, the majority (39 out of 52) of the cited references now appear before the Results section.
- The scheme shown in the figure in the results is more suitable for a chapter where the methodological procedure should be described in detail.
Response: We appreciate the reviewer’s suggestion. However, we believe that moving these figures to the Materials & Methods section would disrupt the flow of the article. The figures in question were developed based on the results of our research, specifically the water quality analysis, and not from the methodologies. The AWPF scheme, for example, could not have been constructed without first analyzing the water quality data. For this reason, we have decided to retain the figures in the Results section.
- The table in the conclusion is generally a presentation of the results. Here it is necessary to specify the state of the art of your research...
Response: Thank you for your insightful comment. To avoid any confusion, we have relocated Table 3 to the end of the Discussion section. The Conclusion section now focuses exclusively on discussing the novelty and significance of our research.
Round 3
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have made an effort to improve the quality of scientific paper. It really looks more presentable now and I think it will be interesting for researchers-readers. I would just like to add one more suggestion. In the conclusion, you nicely drew attention to the continuation of the research, but it would be interesting if, at least in a few sentences, you could specifically state the scientific contribution of your research up to today.
Author Response
The authors have made an effort to improve the quality of scientific paper. It really looks more presentable now and I think it will be interesting for researchers-readers. I would just like to add one more suggestion. In the conclusion, you nicely drew attention to the continuation of the research, but it would be interesting if, at least in a few sentences, you could specifically state the scientific contribution of your research up to today.
Response: We sincerely appreciate Reviewer 2 for the time and effort to review and improve this manuscript again. To address this reviewer’s comment, we have added the following two sentences at the end of the Conclusion section:
This research provides a critical foundation for future regulatory frameworks and policy development by demonstrating the potential of integrating stormwater into potable water reuse systems, paving the way for innovative water management strategies in regions facing water scarcity. It also offers new insights into the practical application of stormwater and reclaimed water blending, contributing to the development of sustainable, closed-loop water systems.
