Operation of a Zero-Discharge Evapotranspiration Tank for Blackwater Disposal in a Rural Quilombola Household, Brazil

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Article- Evapotranspiration Tank – A Case Study of a Decentralized Sanitation Solution in a Rural Quilombola Household, Brazil

1. The study is based on a single household system without a control or comparison setup like conventional septic tank….., which limits the generalizability of findings.
2. Although 218 days is substantial, it still only covers one seasonal cycle (rainy). Lack of dry season data limits the understanding of full-year system behavior.
3. The water balance does not account for infiltration, leaks, or plant uptake variability, which could introduce errors or under-/overestimation of evapotranspiration. Can you include this too
4. The quality of treated water (if any), soil, or plant tissue is not analyzed, missing an opportunity to assess environmental or health risks. Include this too if possible
5. The use of a constant (1.09) for fecal and urinary contribution assumes uniform behavior across individuals, which may not reflect real variation in a diverse household. Comment.
6. There is no calibration data or discussion on accuracy or uncertainty related to the mechanical level meter or water meter used, which could affect data precision.
7. Details on system maintenance, user compliance, or variation in water use behavior during the monitoring period are missing—these are critical in decentralized systems.
8. The conclusions overlook important limitations such as limited sample size, short duration i.e., 7 months, and lack of effluent quality data—despite these being mentioned in the results/discussion.
9. Although mentioned in recommendations, pathogen/nutrient fate and plant/fruit safety should be flagged more strongly as essential next steps, especially for systems involving food production.
10. The conclusion could better connect the TEvap system to larger sanitation goals like SDG 6 or national rural sanitation strategies.
11. The unique characteristics of the pilot site (climate, plant choice, materials) may limit replication, but this is not acknowledged in the conclusion.
12. While low-cost materials are used, there is no cost-benefit analysis, payback period, or operational cost estimate to support large-scale adoption. While cost-effectiveness is noted in recommendations, no indication is given of actual costs incurred or how they might compare with other systems. This reduces the utility for policymakers.

Comments on the Quality of English Language

can be improved

Author Response

Comments 1: The study is based on a single household system without a control or comparison setup like conventional septic tank….., which limits the generalizability of findings.

Response 1: Dear Reviewer, thank you for the valuable contributions. The implementation of the evapotranspiration tank (TEvap) as a nature-based, zero-liquid-discharge solution was an innovation in the studied quilombola community, as all households previously discharged fecal sewage into rudimentary pits—without any soil impermeabilization. However, the TEvap could be compared to other technologies such as the septic tank, but it offers additional benefits. In the septic tank, the treated effluent is infiltrated into the soil, whereas in the TEvap, it is reused by plants through the process of evapotranspiration. This point has been addressed in the revised version of the present manuscript.

Inserted text (Lines 340-344):

Simple construction technologies with low cost and reduced maintenance requirements, such as the TEvap, could replace the combination of septic tanks and infiltration systems [29], and with lower implementation costs [25]. Maintenance refers to occasional pruning, control of cultivar growth, and removal of excess sludge after a certain period, for example, every 4 to 5 years [32].

 

Comments 2: Although 218 days is substantial, it still only covers one seasonal cycle (rainy). Lack of dry season data limits the understanding of full-year system behavior.

Response 2: Dear Reviewer, thank you for your observation. The aim of the article is precisely to present the initial monitoring of the TEvap, making it reasonable to cover only a single season within the annual cycle, especially considering that no previous studies in the literature have reported this type of monitoring. However, the TEvap remains an ongoing object of study and will also be analyzed during the dry season. We have emphasized in the manuscript the specific season considered for monitoring, and in the recommendations section, we suggest that future studies should carry out longer monitoring periods (Lines 136; 464-467).

 

Comments 3: The water balance does not account for infiltration, leaks, or plant uptake variability, which could introduce errors or under-/overestimation of evapotranspiration. Can you include this too

Response 3: Dear Reviewer, thank you for contributing to the improvement of our article. We believe this issue is crucial to advancing the discussion and highlighting some of the limitations of the present manuscript. As suggested, this point has been addressed in the methodology and recommendations sections of the revised version of the manuscript (Lines 198-200; 496-502).

 

Comments 4: The quality of treated water (if any), soil, or plant tissue is not analyzed, missing an opportunity to assess environmental or health risks. Include this too if possible

Response 4: Dear Reviewer, although the TEvap is a zero-liquid-discharge system—meaning the final effluent is entirely evapotranspired—two inspection pipes were installed during its construction (at the effluent inlet and the midpoint of the system). Sewage samples were collected from two distinct points within the TEvap, and analyses of pH, electrical conductivity, color, turbidity, COD, and BOD were performed. These details have been included in the revised version of the manuscript: Methodology (Lines 168-182); Results (Lines 233-241); Discussion (Lines 382-387); Conclusions (Lines 508-510).

Regarding soil or plant tissue analyses, these were not carried out; however, this limitation has been added to the recommendations for future studies (Lines 487-490).

 

Comments 5: The use of a constant (1.09) for fecal and urinary contribution assumes uniform behavior across individuals, which may not reflect real variation in a diverse household. Comment.

Response 5: Dear Reviewer, yes, a value of 9% was assumed to represent the per capita contribution of fecal sewage equally among all household members. However, we agree that this may have led to an overestimation, given the diverse composition of the family. For this reason, we have included a remark on this limitation in the manuscript. The estimation was necessary, as it was not feasible to install a volumetric meter at the toilet outlet to quantify the actual sewage generation.

Inserted text (Lines 156-158):

 The use of this value equally among the eight individuals in the household analyzed in this study may have overestimated the Cp data, since not all of them are adults.

 

Comments 6: There is no calibration data or discussion on accuracy or uncertainty related to the mechanical level meter or water meter used, which could affect data precision.

Response 6: Dear Reviewer, periodic visits were conducted at the TEvap to ensure the accuracy of the readings from the measurement instruments. Whenever necessary, adjustments were made to the mechanical level gauge to ensure its proper functioning (e.g., checking pulleys and fishing lines). Regarding the water meter, it was tested for performance by the Goiás Sanitation Company (Saneago) prior to installation, and the results confirmed an error margin of less than 5%. Additionally, the mechanical level gauge was tested in the laboratory to verify its reliability. To clarify these aspects and improve the manuscript, this information has been included in the revised version.

Inserted text (141-144):

For this, a mechanical level meter composed of a float and pulley was used (Figure 3a), being tested in the laboratory, with periodic field visits conducted for adjustments and to ensure proper functioning.

Inserted text (150-153):

To ensure reading accuracy, the volumetric meter was subjected to performance verification tests by the Goiás Sanitation Company (Saneamento de Goiás S.A. – Saneago), which confirmed an error of less than 5%.

 

Comments 7: Details on system maintenance, user compliance, or variation in water use behavior during the monitoring period are missing—these are critical in decentralized systems.

Response 7: Dear Reviewer, thank you for your valuable observation. Regarding system maintenance, the TEvap is a relatively simple solution and does not require complex maintenance, aside from the removal of a plant at the end of its productive cycle or in cases where a plant does not survive in the evapotranspiration bed. In addition, another maintenance activity involves the removal of excess sludge after a certain period. The literature offers limited information on the lifespan of TEvaps; however, a literature review presented by Reis et al. [32] suggests sludge removal after approximately 4 to 5 years of operation. In the TEvap evaluated in the present study, the sludge removal interval may be equal to or longer than the period reported in the literature.

These details have been added to the manuscript to expand the discussion on this topic.

Inserted text (Lines 340-344):

Simple construction technologies with low cost and reduced maintenance requirements, such as the TEvap, could replace the combination of septic tanks and infiltration systems [29], and with lower implementation costs [25]. Maintenance refers to occasional pruning, control of cultivar growth, and removal of excess sludge after a certain period, for example, every 4 to 5 years [32].

 

Regarding user compliance or variation in water use behavior during the monitoring period, it is known that per capita fecal sewage contribution (Cp) values can vary due to changes in water usage. Such changes may result from various factors, including festivities, school holidays, travel, or extended visits from relatives, as evidenced by Silva, Scalize, and Albuquerque [55] in their analysis of Cp data from six households across six rural quilombola communities, including the one featured in the present study. This approach is already addressed in the manuscript; however, an additional explanation has been included to further elaborate on this aspect.

Inserted text (Lines 438-440):

Cp values can vary depending on water use behavior. Thus, factors such as holidays, visits, family gatherings, or trips to the city can also significantly impact the volume of water used daily in households [55].

 

Comments 8: The conclusions overlook important limitations such as limited sample size, short duration i.e., 7 months, and lack of effluent quality data—despite these being mentioned in the results/discussion.

Response 8: Dear Reviewer, thank you for your thoughtful comments, which helped us improve our article. The limitations you mentioned have been included in the revised version of the manuscript. However, regarding the effluent quality data from the TEvap, sewage analyses were indeed conducted, although this information had not been previously included. We have now expanded the original scope of the article, and these new data have been incorporated into the manuscript: Methodology (Lines 168-182); Results (Lines 233-241); Discussion (Lines 382-387); Conclusions (Lines 508-510).

In addition, we included more details in the conclusion section, highlighting the key findings of the research alongside the study’s limitations (Line 503).

 

Comments 9: Although mentioned in recommendations, pathogen/nutrient fate and plant/fruit safety should be flagged more strongly as essential next steps, especially for systems involving food production.

Response 9: Dear Reviewer, we agree that greater emphasis is needed regarding sanitary precautions related to the potential use of fruits produced in the TEvap bed. For this reason, we have included additional considerations in the manuscript, specifically in the recommendations section.

Inserted text (Lines 484-491):

The goal of the TEvap is not to cultivate plants for harvest, and the cultivated species are not necessarily intended for consumption. However, this type of technology can not only enhance the landscape aesthetically but also potentially produce edible fruits. In such cases, microbiological analyses of the fruits are essential to ensure safe consumption. In this regard, it is recommended that long-term evaluations be conducted on the composition of the effluent and the soil within the TEvap, as well as their effects on the cultivated plants and the generated sludge. This will ensure that the system is not only functional but also safe for the environment and public health.

 

Comments 10: The conclusion could better connect the TEvap system to larger sanitation goals like SDG 6 or national rural sanitation strategies.

Response 10: Dear Reviewer, thank you for your valuable comment. As suggested, we further emphasized the connection between the TEvap and broader sanitation goals, including SDG 6 and the targets of national rural sanitation policies, in the final considerations of the conclusion section. Overall, we highlighted how the cost-effectiveness, simplicity, and environmental performance of the TEvap align with the urgent need to achieve universal access to clean water and sanitation. We appreciate this insightful observation, which helped strengthen the impact of the manuscript.

Inserted text (Lines 518-525):

Overall, the TEvap proved to be an effective, nature-based, zero-discharge solution for blackwater treatment in rural communities. Considering local conditions was crucial for the successful implementation of the solution. More broadly, the TEvap stands out as a promising example of social technology that can contribute to the goals of the national rural sanitation policy. When implemented in areas lacking basic sanitation, this ecological technology can help promote health and improve the quality of life of the served communities—especially given the urgency of meeting SDG 6 (clean water and sanitation for all).

 

Comments 11: The unique characteristics of the pilot site (climate, plant choice, materials) may limit replication, but this is not acknowledged in the conclusion.

Response 11: Dear Reviewer, we acknowledge that the unique local conditions could have been better addressed in the discussion regarding replicability in other regions. Therefore, we have included this approach in greater detail and connected it with other relevant topics in the discussion and recommendations sections.

Inserted text (Lines 424-429):

The water level in the TEvap (Fig. 6) is regulated not only by the stage of plant growth but also by climatic conditions and sewage inflow (Fig. 7). This study highlighted this through a strong Pearson correlation (p < 0.001) between sewage level and relative humidity (rp = 0.75) and per capita contribution (rp = 0.28), emphasizing the importance of sizing adapted to local conditions and water use behavior.

 

Inserted text (Lines 464-483):

Long-term monitoring, exceeding 12 months, is recommended as it is essential to evaluate the system's cost-effectiveness in treating domestic blackwater compared to other solutions (wetlands, septic tanks, etc.) under different climatic and seasonal conditions (rainy and dry season). It is suggested that other TEvaps with a diversity of plants (papaya, taro, among others) and/or other filling materials (rubble, gravel, among others) be monitored, as a replacement for tires, bricks, crushed stone, and sand, for example. Additionally, to ensure system resilience under extreme climatic conditions—such as excessive rainfall or prolonged droughts—it is recommended to include a safety margin in the design.

Evapotranspiration can be measured by phenological stage (e.g., sprouting, vegetative growth, flowering), and soil moisture sensors or evapotranspiration models should be used to quantify the water demand at each growth stage of the cultivar. For this purpose, microclimatic factors (such as relative humidity and solar radiation) should be considered and statistically correlated with system efficiency.

When installing the TEvap in other regions, its efficiency may be equal to or even greater than the values observed in this study, provided that the evapotranspiration rate does not exceed the local precipitation. To ensure optimal performance, the selected plants should have high water demand and be adapted to the specific climate of each region. In temperate or cold regions, willows (Salix sp.) could efficiently replace banana plants (Musa spp.), which are well adapted to tropical and subtropical climates.

 

Comments 12: While low-cost materials are used, there is no cost-benefit analysis, payback period, or operational cost estimate to support large-scale adoption. While cost-effectiveness is noted in recommendations, no indication is given of actual costs incurred or how they might compare with other systems. This reduces the utility for policymakers.

Response 12: We agree that this approach could have been included in the previous version of the manuscript to support the large-scale adoption of the solution and to compare it with other decentralized sanitation technologies in rural areas. Therefore, the construction cost of the TEvap has now been presented in the manuscript.

Inserted text (Lines 113-117):

Banana plants were purchased free of charge from the community. The total cost of materials was US$701.7 (R$3,465.5) [38], and may vary depending on local prices and the use of donated materials. An economic analysis, which was not performed in this study, is recommended to demonstrate the cost-benefit viability compared to other ecotechnologies.

Dear Reviewer, thank you for your valuable contributions to the manuscript. All suggestions were carefully considered and have been incorporated into the revised version. We believe that the changes made fully address the comments provided and contribute significantly to improving the quality of the work.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript discusses the concept of using evapotranspiration tank as a small-level sewage treatment facility. The revised manuscript has not made any visible modification except change of the word BET to TEvap. I am interested to know what were the earlier review comments that made you to retain the manuscript as such.

1. The concept of using TEvap for sewage treatment is not novel and the process has been studied in detail in the literature. The scope of the present study is highly limited and does not contribute to any meaningful conclusion about the treatment viability.
2. There is no research challenge or problem statement in this paper. It is only a case study report, which has limited scope of applicability compared to the research space.
3. The title is to be corrected in terms of language, impression of the idea and key scope of the study. It is somewhat misleading. Since the study focuses only on flow variation, it should be highlighted.
4. The abstract does not convey any cause-evidence-effect type of analysis. It is merely a description of the study without any purpose and finding. The study seriously lacks scientific vigour in the abstract.
5. The introduction has to bring about the state-of-the-art research status of the topic. The objectives do not carry any significance as such. The objectives should answer some of the questions like: Why do you want to do this study? Why do you choose this methodology? What is that you want to learn from this? How do you want to communicate it?
6. The public involvement in the project is a great thing. But the authors should have used some methodology to make it as a research step.
7. The authors have not formatted the paper for the journal. They don’t use English in many places in the manuscript. For e.g. Fig. 2 caption.
8. The parts are not correctly and completely marked in Fig. 2.
9. L154: what is Becker?
10. Is Eq. 1 time-averaged? How did you account for the possible interventions such as side-leaching and infiltration?
11. All the terms in Eq. 1 are not correctly explained. Use of notations are not uniform in the following paragraph.
12. The results have to be properly organized and presented under different subsections.
13. Since the sewage flow has considerable variations compared to rainfall or ET, what are the regulatory measures installed in the system to equalize the variability? Or did the authors account for such variabilities as a consequence of the process mechanisms?
14. What is the significance of 51 days? How to account for the extreme weather conditions to maintain the mass balance and proper water utilization?
15. The authors use the terms “sewage water” and “blackwater” consequently. Do they represent different or same in this study?
16. Check the spelling of “initial” in Table 1.
17. How do the authors account for the variability shown in Fig. 6 for the result shown in Fig. 5?
18. What is the significance of 9%? On what basis it is fixed? Similarly, the averaging of Cp values is also not justified.
19. L258: the term Cp is used before explaining it first.
20. The ET requirement of the crop generally varies with the growth stage. How do the variations in influent conditions affect the ET requirements?
21. What is the significance of the surface area of the TEvap in design and how it is adopted in the present study?
22. The discussion part lacks in proper statistical indicators in evaluating the trends and correlations.
23. The conclusion section has to be rewritten with proper key points.
24. The recommendation section has to be mentioned before the conclusion.
25. Need to prepare the references in the required format.

Comments on the Quality of English Language

The use of English language must be improved to minimise the errors and enhance the readability.

Author Response

General comment: The manuscript discusses the concept of using evapotranspiration tank as a small-level sewage treatment facility. The revised manuscript has not made any visible modification except change of the word BET to TEvap. I am interested to know what were the earlier review comments that made you to retain the manuscript as such.

Response: Dear Reviewer, we would first like to respond to your question regarding editorial pre-checking.

The Academic Director made comments regarding the title regarding the use of the term evapotranspiration tank or basin; the community typology (quilombola); and the use of the term “fecal sewage”. These comments were responded to and changed in the manuscript.

Editor's Comment:

Comments (part 1): Some terminology/language used in the current version of the manuscript seems that can be improved. The term “Evapotranspiration Basin” present in the Title, for example, does not seem to be the most suitable. It can be replaced by Evapotranspiration System, Evapotranspiration Bed, or similar. Also, Quilombola Household is not universally known (is specific from Brazil?). A possible solution for the Title can be, for example, perhaps, between many others, “Evapotranspiration System – A Case Study of a Decentralized Sanitation Solution in a Rural Quilombola Household, Brazil”, or similar.

Answer: Dear Editor, thank you for your considerations. The title was changed to better standardize the terms in relation to the articles published on this topic. The term 'quilombola' designates one of the typologies of traditional communities in Brazil, referring to groups formed by remnants of quilombos — former territories of resistance and refuge for enslaved people. This is described in the introduction to this article (lines 47-50).

New article title: “Evapotranspiration Tank – A Case Study of a Decentralized Sanitation Solution in a Rural Quilombola Household, Brazil”

Comments (part 2): Also, the term “faecal sewage” (Lines 11, 13, and 19 of the Abstract) does not seem the most appropriate in technical terms and can be replaced by blackwater, toilet waste, wastewater, or similar. The Authors should improve these small language details in a minor revision, perhaps preferably before the submission be sent to peer review.

Why was the water meter connected only to the toilet? Do the analyzed households not use other sanitary equipment (e.g., sinks)?

Answer: Dear Editor, we appreciate your contribution to improving our work, the term fecal sewage was replaced by blackwater as it is a term commonly used in the literature in studies on this topic.

Dear Reviewer, the line numbers in the responses to the Editor refer to the previous version submitted for peer review.

Below are your comments, and corresponding responses.

Comments 1: The concept of using TEvap for sewage treatment is not novel and the process has been studied in detail in the literature. The scope of the present study is highly limited and does not contribute to any meaningful conclusion about the treatment viability.

Response 1: Dear Reviewer, thank you for your observation. We agree that the concept of evapotranspiration systems (TEvap) has been previously described in the literature. However, we believe our study offers relevant contributions by exploring the performance of the TEvap in a specific context—a rural quilombola household—which has not yet been addressed in prior research.

In addition, this work aims not only to monitor the system’s functioning but also to understand its application as a decentralized sanitation solution in rural areas lacking infrastructure, while integrating both environmental and social aspects.

We revised the manuscript to include new information and provide a clearer contextual approach, in order to highlight the gaps this study aims to address. The scope of the research was expanded to include an analysis of the sewage within the TEvap system. Methodology (Lines 168-182); Results (Lines 233-241); Discussion (Lines 382-387); Conclusions (Lines 508-510) and construction cost (Lines 113-117).

We also reinforced the study’s limitations, as suggested, acknowledging that this is a sanitation solution implemented in a small sample of households. However, it provides valuable insights and a foundation for future large-scale applications (Line 470).

 

Comments 2: There is no research challenge or problem statement in this paper. It is only a case study report, which has limited scope of applicability compared to the research space.

Response 2: We appreciate the constructive criticism. We agree that clearly defining the research problem is essential to highlight the relevance of a study. Based on this observation, we revised the introduction section to explicitly state the challenge addressed: the lack of safe, low-cost, and feasible sanitation solutions for marginalized rural communities, such as the quilombola household examined in this study.

Although it is a case study, it addresses a concrete and recurring issue in contexts of territorial exclusion, where conventional sanitation alternatives are not viable. We believe this gives the work a crucial contribution, especially in the field of applied research on decentralized sanitation and environmental justice.

Additionally, we included a clearer statement of the problem in the manuscript (Lines 35-70) and of the research objective, highlighting the intention to assess the technical and environmental feasibility of the TEvap system in this specific context (Lines 63-70).

We also revised the discussion section to better connect the study’s findings with broader debates on nature-based solutions and public policies for rural sanitation.

 

Comments 3: The title is to be corrected in terms of language, impression of the idea and key scope of the study. It is somewhat misleading. Since the study focuses only on flow variation, it should be highlighted.

Response 3:

Dear Reviewer, thank you for your observation. We agree that the previous title did not accurately reflect the main focus of the study, which is the analysis of sewage flow variation within the TEvap system implemented in a rural household.

The title has been revised to better highlight the scope of the research and to avoid any misinterpretation regarding the study’s breadth. We hope that the new version is more aligned with the content presented.

New title: “Blackwater flow dynamics in an evapotranspiration tank implemented in a rural quilombola household, Brazil”

Comments 4: The abstract does not convey any cause-evidence-effect type of analysis. It is merely a description of the study without any purpose and finding. The study seriously lacks scientific vigour in the abstract.

Response 4: Dear Reviewer, thank you for the constructive criticism regarding the abstract. Indeed, the previous version did not clearly present the scientific structure of the study. The abstract has been revised to emphasize the study’s objective, the main results with quantitative data, and the relevance of the proposed solution. We hope the new version conveys the evidence, purpose, and scientific contribution of the study more clearly and objectively.

New abstract (Lines 12-24):

“Ecological and low-cost solutions have been adopted for decentralized sanitation in rural areas. This study analyzed the flow of blackwater inside an evapotranspiration tank (TEvap), constructed with community participation in a rural quilombola household in the Central-West region of Brazil. The system, with an area of 8.1 m² (1.0 m² per inhabitant), was monitored for 218 days during the rainy season. After 51 days, the TEvap reached equilibrium, operating under a zero-discharge regime and removing 92.3% of the total volume of water entering the TEvap (40.58 m³) through evapotranspiration and absorption by the cultivated plants (Musa spp.). Statistical analyses indicated significant correlations (p < 0.001) between sewage level and variables such as relative air humidity, temperature, and per capita fecal sewage contribution, demonstrating the influence of climatic factors on system efficiency. The stabilization of the internal level and the good performance of the TEvap confirm its potential as a natural solution for domestic sewage treatment in vulnerable communities.”

 

Comments 5: The introduction has to bring about the state-of-the-art research status of the topic. The objectives do not carry any significance as such. The objectives should answer some of the questions like: Why do you want to do this study? Why do you choose this methodology? What is that you want to learn from this? How do you want to communicate it?

Response 5: Dear Reviewer, we sincerely thank you for your observation. Based on this valuable contribution, we have revised the introduction and objectives of the manuscript to better clarify: the current status of research on TEvap systems, highlighting their advances and limitations; the existing gap regarding the operation and monitoring of real-scale systems in rural contexts; the rationale for adopting a case study methodology integrating technical and social aspects; and the study’s aims to understand the challenges, limitations, and potentials of the TEvap under real-use conditions (Lines 35-61).

More specifically, we made it explicit that the research aims to fill a relevant gap in practical knowledge regarding the hydraulic behavior of real-scale TEvap systems, with the goal of supporting future applications in similar contexts. The choice of an interdisciplinary approach was also emphasized as fundamental to understanding the adaptability and community participation in the implementation of social technologies.

New abstract (Lines 62-69):

Thus, this study aims to evaluate the initial operation of a full-scale, zero-discharge TEvap system receiving blackwater from a household located in a rural quilombola community in Central Brazil. Specifically, the study investigates the system’s hydraulic behavior, identifying potential challenges and its adaptability to the local context. An interdisciplinary methodology was adopted, combining technical monitoring with participatory approaches involving local residents. Through this integrated analysis, the study seeks to contribute to the applied knowledge of decentralized sanitation technologies, particularly those aimed at marginalized rural populations.

Comments 6: The public involvement in the project is a great thing. But the authors should have used some methodology to make it as a research step.

Response 6: Dear Reviewer, thank you for the relevant observation. The methodology regarding community participation has been included in the manuscript in a separate section.

New abstract (Lines 123-125):

Community participation was documented through on-site observation and open dialogues, using photographs, notes, and field reports [39,40].

Comments 7: The authors have not formatted the paper for the journal. They don’t use English in many places in the manuscript. For e.g. Fig. 2 caption.

Response 7: Dear Reviewer, thank you for your comment. We have thoroughly revised the manuscript formatting in accordance with the journal’s guidelines. All previously non-compliant sections have been corrected, including the legend of Figure 2 (Line 119), which is now entirely in English. We also reviewed figures, tables, axis titles, abbreviations, and expressions that were in Portuguese, ensuring language consistency throughout the text.

Comments 8: The parts are not correctly and completely marked in Fig. 2.

Response 8: Dear Reviewer, thank you for your observations. We have adequately specified all the items in Figure 2 (Lines 118-119).

Comments 9: L154: what is Becker?

Response 9: Dear Reviewer, thank you for pointing this out. There was a typographical error in the writing, and the intended word was “beaker.” This has now been corrected (Line 164).

Comments 10: Is Eq. 1 time-averaged? How did you account for the possible interventions such as side-leaching and infiltration?

Response 10: Dear Reviewer, thank you for your comments. Regarding Eq. 1, it was used to calculate the cumulative balance, not temporal averages. This information has been added to the text for greater clarity and to facilitate potential replication of the method in other contexts or temporal scales (monthly or seasonal analysis).

Inserted text (Lines 200-202):

The equation was applied cumulatively for the total monitoring period (218 days), as well as for the progression period (51 days) and stabilization period (167 days) in relation to the sewage level in the TEvap.

Regarding possible losses by lateral leaching and infiltration, we clarify that these flows were disregarded in the water balance due to the sealing of the TEvap (impermeabilization with additive and bituminous mass) and the absence of anomalous variations in the internal level throughout the monitoring period.

For better understanding, these technical specifications have been added to the methodology section of the manuscript, and additional construction details have been included in Figure 2.

Inserted text (Lines 101-106):

To create the watertight compartment of the TEvap, masonry was used with the addition of a waterproofing additive (Vedacit®), and finished with a bituminous coating (MastFrio Asfalto, Usina Anchieta®). The bottom slab was constructed using reinforced concrete with chain-link mesh (1.9 mm wire, Vonder®). The walls were built 0.10 m above ground level (G.L., Figure 2a), forming a containment curb to prevent flooding from rainwater.

Additionally, this methodological limitation has been acknowledged in the recommendations section, where we suggest that future studies employ appropriate instrumentation to monitor these potential losses, when present.

Inserted text (Lines 499-502):

In the present study, the water volume associated with infiltration, leaks, or variability in plant absorption was not considered in the water balance calculation. Future studies could employ appropriate instrumentation to monitor these potential losses in order to reduce errors or under/overestimation of evapotranspiration.

Comments 11: All the terms in Eq. 1 are not correctly explained. Use of notations are not uniform in the following paragraph.

Response 11: Dear Reviewer, the terms in Eq. 1 have been correctly explained, ensuring consistency throughout the information provided (Lines 203-208).

Comments 12: The results have to be properly organized and presented under different subsections.

Response 12: Dear Reviewer, thank you for the suggestion. The adjustments have been incorporated into the manuscript.

Results (Line 214):

3.1. Community involvement in the construction of the TEvap (Line 215);

3.2. TEvap Monitoring (Line 233)

3.2.1. Assessment of the fecal sewage inside the TEvap (Line 234)

3.2.2. Fecal sewage levels inside the TEvap and water balance (Line 242)

Comments 13: Since the sewage flow has considerable variations compared to rainfall or ET, what are the regulatory measures installed in the system to equalize the variability? Or did the authors account for such variabilities as a consequence of the process mechanisms?

Response 13: Dear Reviewer, thank you for your valuable observation. The TEvap was designed as a nature-based solution without active hydraulic equalization devices. We chose to rely on the system’s inherent processes—such as evapotranspiration, controlled infiltration in the filter bed, and plant uptake—to manage flow variability. This limitation, along with the possibility of incorporating additional control mechanisms in future scenarios (such as retention chambers or modular systems), has been included in the recommendations section for future studies.

Inserted text (Lines 496-498):

When variability in sewage flow is not adequately absorbed by natural mechanisms, the installation of retention chambers or modular systems is recommended.

However, the system is equipped with an emergency overflow installed at a height of 78 cm as a safety measure (Fig. 2; Line 118), although it was not activated during the monitored operation period. The behavior observed over the 218 days—with stabilization of the internal sewage level and absence of overflow—indicates that, under the evaluated operational conditions, the variability was adequately absorbed by the system’s natural mechanisms.

Comments 14: What is the significance of 51 days? How to account for the extreme weather conditions to maintain the mass balance and proper water utilization?

Response 14: Dear Reviewer, thank you for raising this point and prompting us to reflect further on the topic.

The 51 days represent the period during which the blackwater level showed a clear upward trend (linear tendency, R² = 0.955). During this phase, the limited evapotranspiration capacity of the young plants allowed water to accumulate, primarily due to the input of fecal sewage. In other words, from the 51st day onward, the evapotranspired volume began to offset the inflow of blackwater, maintaining the level below the overflow pipe.

In this regard, we have added to the manuscript that the equilibrium period considered was specific to the local conditions of the study—including climate, soil type, plant species, and initial irrigation—and should not be generalized without proper adjustment to these variables.

Inserted text (Lines 278-280):

This equilibrium time depends on factors such as climate, type and number of plants, irrigation, and input volume, and should not be generalized without proper adjustment to these variables.

 

Regarding extreme weather conditions, we acknowledge that the system’s performance may be affected in scenarios of excessive rainfall or prolonged drought. Therefore, the article recommends long-term monitoring and, for future projects, the inclusion of safety margins in the design, as well as the possibility of incorporating additional control devices. These considerations have been included in the recommendations section of the revised manuscript.

Inserted text (Lines 470-472):

Additionally, to ensure system resilience under extreme climatic conditions—such as excessive rainfall or prolonged droughts—it is recommended to include a safety margin in the design.

 

Comments 15: The authors use the terms “sewage water” and “blackwater” consequently. Do they represent different or same in this study?

Response 15: Dear Reviewer, thank you for the relevant observation. In the manuscript, we exclusively used the term “blackwater,” as the type of wastewater considered includes only fecal matter (feces and urine), excluding greywater—wastewater from showers, kitchen sinks, and washing machines.

Comments 16: Check the spelling of “initial” in Table 1.

Response 16: Dear Reviewer, thank you for pointing out this typographical error. The word has been corrected, and due to revisions made in the manuscript, the referenced table is now Table “2.” (Lines 282-283).

 

Comments 17: How do the authors account for the variability shown in Fig. 6 for the result shown in Fig. 5?

Response 17: Dear Reviewer, due to the revisions, Figure 6 has become Figure 7, and Figure 5 is now Figure 6 in the corrected version of the manuscript.

During the filling phase (P1), water accumulation (0 → 40.1 cm) (Figure 6a) occurred despite the per capita contribution (Cp) (12.07 L/person/day, Figure 7a) differing by only 1.73 L/person/day from the long-term average (13.80 L/person/day), due to low evapotranspiration by the young plants and absence of rainfall.

In the equilibrium phase (P2), stable levels (35.7–51.0 cm) reflect increased evapotranspiration (98.6%), with the banana plants undergoing vegetative elongation (Fig. 5f–i), probably balanced by rainfall (13.39 m³), as Cp was variable (0.36–27.6 L/person/day, Fig. 7a).

To improve the connection between the information presented in the figures analyzed, this approach was added to the discussion. Additionally, we included a statistical correlation analysis between the variables shown in Figures 6 and 7.

Inserted text (Methodology, lines 211-213):

Pearson correlation analyses were conducted between the data on precipitation, temperature, relative humidity, sewage level, and per capita contribution of fecal sewage for the entire monitoring period, considering a statistical significance level of 95%.

Inserted text (Results, lines 310-318):

The statistical analysis of the variables in Figs. 5 and 6 suggested Pearson correlations (r_p) ranging from weak to moderate (-0.60 < r_p < 0.60) and strong (|r_p| > 0.6) [47]. Cp and temperature, r_p = 0.09 (p = 0.165); Cp and relative humidity, r_p = 0.14 (p < 0.05); Cp and sewage level, r_p = 0.28 (p < 0.001). Sewage level data inside the TEvap showed correlation with relative humidity (r_p = 0.75) and precipitation (r_p = 0.29), both with a significant level (p < 0.001); and a strong negative correlation with temperature (r_p = -0.66), indicating that local climatic factors may influence the performance of the TEvap. However, more robust statistical analyses could better identify these relationships, considering a longer time series and multiple units.

Inserted text (Discussion, lines 399-401):

The drop in sewage level to 35.7 cm on 10/03/25 (Fig. 6a) may be due to an increase in local temperature and a decrease in rainfall during this period, favoring evapotranspiration.

Inserted text (Discussion, lines 424-429):

The water level in the TEvap (Fig. 6) is regulated not only by the stage of plant growth but also by climatic conditions and sewage inflow (Fig. 7). This study highlighted this through a strong Pearson correlation (p < 0.001) between sewage level and relative humidity (rp = 0.75) and per capita contribution (rp = 0.28), emphasizing the importance of sizing adapted to local conditions and water use behavior.

 

Comments 18: What is the significance of 9%? On what basis it is fixed? Similarly, the averaging of Cp values is also not justified.

Response 18: Dear Reviewer, we sincerely appreciate your observation. The value of 9% was assumed to represent the per capita contribution of fecal sewage equally for all household members, based on literature regarding human excretion patterns for a healthy adult [42]. However, we recognize that this may have overestimated the data, given the diverse family composition (three adults, three teenagers, and two children). Accordingly, we have included a note addressing this consideration in the manuscript.

However, considering the contribution of feces and urine (9%), this value results in 15.04 L/person/day (13.80 × 1.09) (Line 308).

We agree that the calculation of Cp is an estimate and may be higher or lower. However, using these estimates was necessary, as measuring the actual volume of feces and urine produced by each of the eight household members in the studied residence was unfeasible for this study.

Inserted text (lines 156-158):

The use of this value equally among the eight individuals in the household analyzed in this study may have overestimated the Cp data, since not all of them are adults.

Regarding the per capita contribution of fecal sewage (Cp), the average volume (13.80 L/person/day) was obtained by measuring the water volume used in toilet flushes through a volumetric meter that was previously tested. This procedure is described in the methodology section.

Inserted text (lines 144-150):

The volume of blackwater that entered the TEvap was obtained indirectly by measuring the volume of water used in flushes. For this purpose, a volumetric water meter with a nominal flowrate (Qn) of 1.5 m³/h, manufactured by the German brand Zenner (model RTK-S, Germany) was installed in the pipe that exclusively feeds the toilet (Fig. 3b). The measurement of the water volume by the water meter, in turn, made it possible to estimate the per capita contribution of blackwater (Cp) based on the total volume of water consumed throughout the entire monitoring period. To ensure reading accuracy, the volumetric meter was subjected to performance verification tests by the Goiás Sanitation Company (Saneamento de Goiás S.A. – Saneago), which confirmed an error of less than 5%.

Comments 19: L258: the term Cp is used before explaining it first.

Response 19: Dear Reviewer, thank you for your observation. The term "per capita contribution of fecal sewage" (Cp) has been reviewed and included at its first mention in the manuscript (Line 149).

Comments 20: The ET requirement of the crop generally varies with the growth stage. How do the variations in influent conditions affect the ET requirements?

Response 20: Dear Reviewer, thank you for the important observation. In the present study, the specific evapotranspiration (ET) of the cultivars used, banana plants (Musa spp.), was not directly measured by growth stage. However, our study allowed us to gather important information enabling us to infer their impact on the TEvap system, such as:

• Sewage level data (Figure 6; Line 263): we observed a progressive stabilization coinciding with the vegetative development of the banana plants (increase in leaf area);
• Water balance (Table 2; Line 283): 92.3% of the incoming volume was eliminated by evapotranspiration (ET), especially during the “equilibrium period” (98.6% efficiency in P2), when the plants were already established (Figures 5f–i), demonstrating a higher ET demand in advanced growth stages; conversely, during the first 20 days, ET was low (27.5% of the volume was removed), associated with initial water stress of the plants and saturation of the materials used in filling the TEvap.

Additionally, the recorded temperature (19.1–29.0°C) and precipitation (0–134 mm/day) data (Figure 6a; Line 263) fall within the optimal range for banana plants [52,59], favoring evapotranspiration (ET).

All of this suggests that ET requirements are critical during advanced growth stages but require specific monitoring in future studies. Therefore, we acknowledge the importance of analyzing variations in influencing conditions and ET needs of the cultivars. Accordingly, we have added a more detailed discussion on this topic in the manuscript (Lines [please insert]) and included recommendations for future work, highlighting the limitations of our study (Lines 435–439).

Inserted text (Lines 411-422):

In the system equilibrium period (167 days), 98.6% (31.04 m³) of the total volume received was removed, predominantly by evapotranspiration [58], a behavior that corroborates theoretical data for banana plants (Musa spp.) in arid ecosystems (Caatinga), where plants with 60 days of growth consume 16.6 L/day, increasing to 34.86 L/day in advanced stages (210 days) [59]. In our study, carried out in the Cerrado (tropical savanna), a similar pattern was observed: in the progression phase (57 days), evapotranspiration (70.6% of the volume removed) reflected the root and leaf establishment of the seedlings (Fig. 5d-e), while in P2 (167 days), the increase in efficiency (98.6%) coincided with intensive vegetative growth (Fig. 5h-i) and greater water demand. This convergence between empirical and theoretical data, even in different biomes, reinforces the direct influence of the phenological stage on the evapotranspiration capacity of TEvap and its effectiveness as a treatment system in different climatic contexts.

Inserted text (Lines 473-477):

Evapotranspiration can be measured by phenological stage (e.g., sprouting, vegetative growth, flowering), and soil moisture sensors or evapotranspiration models should be used to quantify the water demand at each growth stage of the cultivar. For this purpose, microclimatic factors (such as relative humidity and solar radiation) should be considered and statistically correlated with system efficiency.

Comments 21: What is the significance of the surface area of the TEvap in design and how it is adopted in the present study?

Response 21: Dear Reviewer, thank you for your thoughtful questions, which have helped us deepen the reflection in the manuscript.

The area of the TEvap mainly influences its evapotranspiration capacity. A larger area allows for greater exposure to solar radiation and better utilization of plant transpiration. This is crucial to ensure that the volume of sewage produced by the household is offset by evapotranspiration, preventing overflow. However, an area larger than necessary may compromise system efficiency, increase costs, and occupy land unnecessarily.

In the present study, we adopted an area of 1.0 m² per person, referencing the lower range values found in the literature, from 0.6 [23] to 1.25 m²/person [49]. Assuming a higher value—such as 1.5 [20] or 2.0 m²/person [30]—would overestimate the TEvap size. The per capita fecal sewage contribution (Cp) values reported in studies recommending smaller areas are 13.1 [23] and 9.9 [49], close to the values recently identified in quilombola rural communities in Goiás, Brazil [55].

To clarify the importance of the TEvap surface area, we have included a range of reference values from the literature to justify the value adopted in this work and have reformulated this discussion in the methodology section of the manuscript.

Inserted text (Lines 92-95):

The TEvap was constructed with the following dimensions: 5.40 m x 1.50 m x 1.30 m, presenting a surface area of 8.10 m², which is slightly more than 1.0 m²/inhab. This value is between 0.6 [25] and 1.25 m²/inhab. [36] for TEvaps designed as a nature-based solution for domestic sewage treatment in rural households in Brazil.

Inserted text (Lines 369-375):

In the present study, an area of 1.0 m² per inhabitant was adopted, demonstrating suitability for system stabilization. This parameter was based on the lower values found in the literature, 0.6 m²/inhabitant [25] e 1,25 m²/ inhabitant [36], considering the low fecal sewage generation per capita typical of rural communities [55]. Although technical literature suggests larger areas, 1.5–2.0 m²/inhabitant [21,23], the efficiency observed in the TEvap confirms that reduced sizing can be viable when aligned with specific local conditions.

Comments 22: The discussion part lacks in proper statistical indicators in evaluating the trends and correlations.

Response 22: Dear Reviewer, we acknowledge that the discussion predominantly presents a descriptive approach and that the inclusion of statistical indicators could strengthen the analysis of trends and possible correlations. Since the study involves a single unit, an exploratory approach was initially chosen to demonstrate the behavior of a socially and technically implemented technology at real scale.

However, Pearson correlation analyses between the study variables were performed and incorporated into the revised version. Additionally, we included recommendations that future studies with multiple units or longer time series employ more robust statistical analyses to better identify correlations between climatic variables and system performance. This limitation was added to enhance methodological transparency (Lines 316-318).

Inserted text (Methodology, lines 211-213):

Pearson correlation analyses were conducted between the data on precipitation, temperature, relative humidity, sewage level, and per capita contribution of fecal sewage for the entire monitoring period, considering a statistical significance level of 95%.

Inserted text (Results, lines 310-318):

The statistical analysis of the variables in Figs. 5 and 6 suggested Pearson correlations (r_p) ranging from weak to moderate (-0.60 < r_p < 0.60) and strong (|r_p| > 0.6) [47]. Cp and temperature, r_p = 0.09 (p = 0.165); Cp and relative humidity, r_p = 0.14 (p < 0.05); Cp and sewage level, r_p = 0.28 (p < 0.001). Sewage level data inside the TEvap showed correlation with relative humidity (r_p = 0.75) and precipitation (r_p = 0.29), both with a significant level (p < 0.001); and a strong negative correlation with temperature (r_p = -0.66), indicating that local climatic factors may influence the performance of the TEvap. However, more robust statistical analyses could better identify these relationships, considering a longer time series and multiple units.

Inserted text (Discussion, lines 399-401):

The drop in sewage level to 35.7 cm on 10/03/25 (Fig. 6a) may be due to an increase in local temperature and a decrease in rainfall during this period, favoring evapotranspiration.

Inserted text (Discussion, lines 424-429):

The water level in the TEvap (Fig. 6) is regulated not only by the stage of plant growth but also by climatic conditions and sewage inflow (Fig. 7). This study highlighted this through a strong Pearson correlation (p < 0.001) between sewage level and relative humidity (rp = 0.75) and per capita contribution (rp = 0.28), emphasizing the importance of sizing adapted to local conditions and water use behavior.

Comments 23: The conclusion section has to be rewritten with proper key points.

Response 23: Dear Reviewer, thank you for your observation. The conclusion section was revised as suggested, with the inclusion and reformulation of key terms to more clearly synthesize the main findings of the study and their implications.

Inserted text (Discussion, lines 504-517):

This study on the implementation and initial monitoring of an evapotranspiration tank (TEvap) in a rural quilombola household provided important insights regarding its performance under local specificities. The successful implementation of the TEvap was enhanced by community involvement, a factor that proved essential for its long-term sustainability. Operational monitoring over a 7-month period confirmed the zero-discharge performance of the TEvap, highlighting its capacity to treat blackwater by reducing turbidity, COD, and BOD5.

The system exhibited an initial adaptation period for the cultivated plants (Musa spp.), suggesting that initial irrigation or starting the system in sync with the rainy season could optimize its performance. Furthermore, the study revealed that the sewage level in the TEvap stabilized after 51 days of operation, even with rainfall inputs, and that climatic variables such as relative humidity, temperature, and precipitation influence this level. The adopted area of 1.0 m²/inhabitant, which is smaller than those commonly reported in the literature, reinforces the system’s efficiency under the observed conditions.

of the national rural sanitation policy. When implemented in areas lacking basic sanitation, this ecological technology can help promote health and improve the quality of life of the served communities—especially given the urgency of meeting SDG 6 (clean water and sanitation for all).

Comments 24: The recommendation section has to be mentioned before the conclusion.

Response 24: Dear Reviewer, thank you for this suggestion. As you recommended, the Recommendations section was placed before the Conclusion (Line 463).

Comments 25: Need to prepare the references in the required format.

Response 25: The references that were not in the required format by the journal have been properly corrected.

 

Dear Reviewer, we sincerely appreciate all your observations. Your comments have provided essential critical reflection that helped improve the manuscript. We hope that all the issues raised have been adequately addressed.

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript has a special approach, with a great social impact on the Quilombola community, but also on environmental protection and ecological education regarding wastewater treatment in the community.

The Introduction chapter is well-founded, with recent citations and on the subject addressed, it mentions the SDGs achieved through this research and what the solutions would be for treating wastewater in the communities. It would be recommended to pay more attention to this chapter to clearly mention the objectives of this research and the justification for choosing it.

In the Materials and Methods Chapter, the area studied is described appropriately, with a representative map, and even though the number of inhabitants is 8, it has a high civic value, considering that it is an isolated community.
The material, plants and the location of TEvap are described in detail, this chapter being well founded.

The results are clearly expressed, both numerically and in the form of graphs, as well as with pictures from the implementation of the experiment. The Discussion presents the advantage of using such a solution, as well as the importance of protecting the environment from wastewater infestation.

The conclusions chapter could be further developed, and it is also very important to specify what future research can be undertaken based on this experiment.

 

Author Response

REVIEWER 3

Comments:

This manuscript has a special approach, with a great social impact on the Quilombola community, but also on environmental protection and ecological education regarding wastewater treatment in the community.

The Introduction chapter is well-founded, with recent citations and on the subject addressed, it mentions the SDGs achieved through this research and what the solutions would be for treating wastewater in the communities. It would be recommended to pay more attention to this chapter to clearly mention the objectives of this research and the justification for choosing it.

In the Materials and Methods Chapter, the area studied is described appropriately, with a representative map, and even though the number of inhabitants is 8, it has a high civic value, considering that it is an isolated community.

The material, plants and the location of TEvap are described in detail, this chapter being well founded.

The results are clearly expressed, both numerically and in the form of graphs, as well as with pictures from the implementation of the experiment. The Discussion presents the advantage of using such a solution, as well as the importance of protecting the environment from wastewater infestation.

The conclusions chapter could be further developed, and it is also very important to specify what future research can be undertaken based on this experiment.

This manuscript has a special approach, with a great social impact on the Quilombola community, but also on environmental protection and ecological education regarding wastewater treatment in the community.

Response:

Dear Reviewer, we are immensely grateful for your support and valuable contribution to advancing the discussion in this research area.

Based on your recommendations, the research objective and justification were revised, detailed, and made explicit (Lines 62–69). In the methodology, we included descriptions of additional analyses such as community participation (Lines 120–133; “2.3. Community construction of the TEvap”), construction costs (Lines 113–117), and blackwater sampling inside the TEvap (Lines 168–182; “2.5. Blackwater sampling”).

These contributions were also incorporated into the results and discussion sections, especially regarding the domestic sewage treatment efficiency inside the TEvap (Lines 239; “Table 1”), along with statistical analyses involving variables from Figure 6 (sewage level) and Figure 7 (Cp values) (Lines 211–213).

In conclusion, we revised the text according to your and other Reviewers’ recommendations. Besides improving the flow, we highlighted the importance of community participation (Lines 506–508), the efficiency of blackwater treatment and the study period (Lines 508–510), as well as the TEvap stabilization period and related effects (Lines 511–517).

Additionally, we included the contribution of this work to the achievement of SDG 6 as support for global and national policies (Lines 522–525).

We reinforced the Recommendations section (Line 463), adding current limitations such as seasonality, other plant varieties and materials, effluent and soil composition in the TEvap and their effects on cultivated plants, as well as sludge management, along with key aspects to consider for future studies.

We hope this study contributes to the development of infrastructure projects aimed at improving sanitation in rural areas and provides a solid basis for the formulation of more effective public policies.

We thank you again for your constructive feedback and remain committed to further enhancing the study to make it a relevant and impactful contribution to the field.

Reviewer 4 Report

Comments and Suggestions for Authors

Review comments for manuscript water-3649912

 

The manuscript entitled " Evapotranspiration Tank – A Case Study of a Decentralized 2 Sanitation Solution in a Rural Quilombola Household, Brazil " reported an Evapotranspiration Tank as a solution for wastewater in rural communities. In my opinion, the manuscript needs revisions before being published. Authors may consider the following recommendations to improve the quality of the manuscript:                     

According to the authors, they implemented a wastewater treatment process:

- In the manuscript, I didn't find the characteristics of the raw water before treatment, at least to get an idea of ​​the overall composition of the wastewater.

- The effect of the wastewater composition on the different types of plants considered.

Concerning the construction of the filter bed:

- The choice of the types of filtration media and their depths were based on data from the literature or preliminary studies.

- There is also a lack of information on the porosity of the different layers making up the filter media.

- If possible, add a section concerning the technical and economic study.          

           Conclusion

• The conclusion needs to be improved based on the previous recommendations.

 

Author Response

REVIEWER 4

Comments 1:

The manuscript entitled " Evapotranspiration Tank – A Case Study of a Decentralized 2 Sanitation Solution in a Rural Quilombola Household, Brazil " reported an Evapotranspiration Tank as a solution for wastewater in rural communities. In my opinion, the manuscript needs revisions before being published. Authors may consider the following recommendations to improve the quality of the manuscript: 

Response 1: Dear Reviewer, we sincerely thank you for your support and valuable contribution to advancing the discussion in this research area. We hope this study serves as a starting point for further research with larger samples, enhancing the understanding of sanitation conditions in rural areas.

 

Comments 2: According to the authors, they implemented a wastewater treatment process:

Comments 2.1: - In the manuscript, I didn't find the characteristics of the raw water before treatment, at least to get an idea of ​​the overall composition of the wastewater.

Response 2.1: Dear Reviewer, we sincerely thank you again for your constructive feedback and remain committed to further improving the study.

We acknowledge the importance of presenting the characteristics of the0 influent wastewater in the TEvap monitored in this study. Although these data were previously available, they were not included due to the initially limited scope of the work. Therefore, wastewater samples were collected from two points inside the system—at the inlet and mid-section—after 69 days of operation, and physical-chemical and biological analyses were performed.

These details have been added to the revised manuscript, particularly in the section: Methodology (Lines 168-182); Results (Lines 233-241); Discussion (Lines 382-387); Conclusions (Lines 508-510).

Comments 2.2: - The effect of the wastewater composition on the different types of plants considered.

Response 2.2: Dear Reviewer, thank you for your relevant observation. We agree that the composition of the wastewater (including concentrations of nutrients, salts, etc.) can affect or benefit plant growth and health, which in turn may influence the evapotranspiration rate and overall treatment efficiency.

In the TEvap system, only banana plants (Musa sp.) were used, as they are considered ideal for nature-based sanitation solutions due to their high water demand [33].

However, the scope of the current study did not include a comprehensive analysis of potential plant stress or enhanced growth directly related to wastewater quality. We recognize the importance of this aspect and have added a recommendation for future studies to explore this relationship in greater detail.

Inserted text (Lines 487-491):

In this regard, it is recommended that long-term evaluations be conducted on the composition of the effluent and the soil within the TEvap, as well as their effects on the cultivated plants and the generated sludge. This will ensure that the system is not only functional but also safe for the environment and public health.

 

Comments 3: Concerning the construction of the filter bed:

Comments 3.1: - The choice of the types of filtration media and their depths were based on data from the literature or preliminary studies.

Response 3.1: Dear Reviewer, thank you for your observation. The selection of filling materials (bricks, tires, gravel, and sand) and their respective depths in the TEvap system was based on technical and scientific literature [29].

To provide greater methodological clarity, we have now cited the relevant literature directly in the manuscript (Line 97).

Comments 3.2: - There is also a lack of information on the porosity of the different layers making up the filter media.

Response 3.2: Dear Reviewer, thank you for your important observation. We agree that the porosity of the materials used in the TEvap filling layers directly influences the system’s water storage capacity and internal flow dynamics.

Although the wastewater level did not reach the gravel and sand layers throughout the monitored period, we have included the porosity values of each material in the updated version of the manuscript, within the methodology section. This addition aims to provide a more comprehensive understanding of the system’s hydraulic behavior.

Inserted text (Lines 137-141):

During this period, data on the variation of the sewage level inside the TEvap were collected to determine the volume of water, considering a void ratio in the brick and tire layer of 0.826, in the gravel layer of 0.464 and in the sand layer of 0.448, obtained from tests in an acrylic column to determine the void ratio of the ceramic brick, and jerrycans to determine the volume occupied by the tires [41].

 

Comments 3.3: - If possible, add a section concerning the technical and economic study.

Response 3.3: Dear Reviewer, thank you for your suggestions for improving the manuscript. We've added the construction cost of TEvap to the text; however, the scope of this work doesn't include an economic analysis. We've highlighted this limitation and suggest a cost-benefit economic analysis comparing it with other ecological technologies in future research and similar contexts.

Inserted text (Lines 113-117):

Banana plants were purchased free of charge from the community. The total cost of materials was US$701.7 (R$3,465.5) [38], and may vary depending on local prices and the use of donated materials. An economic analysis, which was not performed in this study, is recommended to demonstrate the cost-benefit viability compared to other ecotechnologies.

Comments 4:   Conclusion: The conclusion needs to be improved based on the previous recommendations.

Response 4: The conclusion section has been revised accordingly (Line 503). We hope to have incorporated all the suggested improvements into the manuscript, clearly emphasizing the key findings and final considerations of the research.

Dear Reviewer, we sincerely appreciate your constructive feedback throughout the review process, which has significantly contributed to enhancing the quality and clarity of our study.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

can be accepted 

Author Response

Response 1: Dear Reviewer, thank you for supporting the acceptance for publication of this manuscript.

We thank you for the general feedback and acknowledge the suggestion that all sections of the manuscript could be improved. In response, we conducted a careful review of the entire text to enhance its clarity, coherence, and scientific rigor. In particular, substantial revisions were made to the abstract (Lines 12-27), conclusion (Lines 511-527), and methodological descriptions—especially the explanation of the statistical significance threshold (Lines 216-218; 316-325)—based on the reviewers’ suggestions. We believe these revisions improved the manuscript and addressed the concerns raised.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have revised the manuscript with many improvements. The following observations are made on the revised version.

1. The abstract is still not up to the mark. Need of research is missing. The statement about statistical significance has to be written in more specific and non-confusing way. The term ‘internal level’ is not appropriate.
2. In the methodology section L213, the authors claim statistical significance of 95%, but the abstract measures significance as P<0.01. rectify.
3. Conclusion may be written as a single paragraph.

Author Response

REVIEWER 2

The authors have revised the manuscript with many improvements. The following observations are made on the revised version.

 

Comments 1: The abstract is still not up to the mark. Need of research is missing. The statement about statistical significance has to be written in more specific and non-confusing way. The term ‘internal level’ is not appropriate.

Response 1: Dear Reviewer, thank you for your observation.

The abstract (Lines 12-27) has been reworded to highlight the problem and the need for research. Clarifying the purpose of the work, the main results with quantitative data and the relevance of the proposed solution.

The term “intermediate level” was removed from the summary for better grammatical adjustment.

We have revised the statement regarding statistical significance to make it clearer and more specific, avoiding ambiguity. The text has been reformulated to explicitly indicate the criterion adopted (p < 0.05), and to clarify that only correlations with p-values below this threshold were considered statistically significant.

 

Comments 2: In the methodology section L213, the authors claim statistical significance of 95%, but the abstract measures significance as P<0.01. rectify.

Response 2: Dear Reviewer, thank you for your observation. We agree that there was an inconsistency between the Methodology section and the Abstract regarding the statistical significance level. We have corrected the Abstract to reflect the threshold adopted throughout the analysis, which is p < 0.05 (95% confidence level), as stated in the Methodology. The text has been revised to ensure consistency across all sections. (Lines 216-218; 316-325).

 

Comments 3: Conclusion may be written as a single paragraph.

Response 3: Dear Reviewer, thank you for contributing to the improvement of our article. The Conclusion section has been revised and is now presented as a single, cohesive paragraph, as recommended. (Lines 511-527).

 

We thank Reviewer for the insightful feedback, which helped enhance the overall quality of the manuscript. We believe the revised version addresses all concerns raised.