Optimization of the Disinfection Process in Potabilization Systems in Cuenca Alto Atoyac, Mexico

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper entitled “Optimization of the disinfection process in potabilization systems in Cuenca Alto Atoyac, Mexico” presents interesting data about the water distribution system and in particular disinfection in Cuenca Alto Atoyac, Mexico. However, the organization of the methodology and results should be clearer and more concise. In its current form, the text is difficult to follow and rather confusing. Many of the results could be omitted or introduced to supplementary material. In addition, the findings of the paper fall into certain limitations that are not clearly presented. The applicability of Polynomial correlations between ORP and total coliform concentration (Table 8) is considerably limited considering that the matrix in each case different (and besides total coliforms other microbes exist as well) and can be significantly changed e.g. due to weather conditions, temperature etc. This is the case also for the results presented in Table 9. I could recommend this manuscript for publication, but only after major revision. I believe that the authors should clarify better the methodology, connect it with specific objectives and present only the results that are aligned with the aims of the study. Otherwise, it is very confusing and wordy.

Minor remarks:

-        Introduction section: Please analyze in more detail the operability of ORP measurements as a tool to capture the effectiveness of disinfection of potable water, since the understanding of underlying mechanisms is crucial, for example, should it be used as single parameter or be used in a set of other parameters? What are the pros and cons? Challenges?

Materials and Methods Section:

-        Figure 2 should be amended as it can confuse the reader. For example, Stage 1 follows three independent “paths”, while it seems that there are only two approaches. Please amend the chart in a simpler format to describe the methodology of the study.

-        Do you have any indications about Total Coliforms and Enterococci? These are crucial parameters regarding the disinfection of drinking water.

-        Please provide in addition data about temperature conditions in the sampling points and testing in the lab, as it can also affect the results.

Results and Discussion:

-        Lines 296-299: Lack of knowledge about water distribution features limits the potential to draw safe and justified conclusions. Data regarding point of chlorination, type of disinfectant, real contact time etc should be clearly presented, where possible (e.g. data could be provided in a Table).

-        Figure 3 shows results that are not presented/discussed (e.g. As, Hg etc).

-        Discussion after clustering (lines 427-464) are general/technical recommendations, without contributing to the aims of the research paper.

 

Comments on the Quality of English Language

English language is adequate

Author Response

Comment 1: The paper entitled “Optimization of the disinfection process in potabilization systems in Cuenca Alto Atoyac, Mexico” presents interesting data about the water distribution system and in particular disinfection in Cuenca Alto Atoyac, Mexico. However, the organization of the methodology and results should be clearer and more concise. In its current form, the text is difficult to follow and rather confusing. Many of the results could be omitted or introduced to supplementary material. In addition, the findings of the paper fall into certain limitations that are not clearly presented. The applicability of Polynomial correlations between ORP and total coliform concentration (Table 8) is considerably limited considering that the matrix in each case different (and besides total coliforms other microbes exist as well) and can be significantly changed e.g. due to weather conditions, temperature etc. This is the case also for the results presented in Table 9. I could recommend this manuscript for publication, but only after major revision. I believe that the authors should clarify better the methodology, connect it with specific objectives and present only the results that are aligned with the aims of the study. Otherwise, it is very confusing and wordy.

Response 1:

We greatly appreciate the reviewer’s comprehensive feedback on our manuscript, as it provides us with valuable insights for significant improvements. Below, we address each point raised with detailed explanations of the actions taken and our rationale:

Clarification and conciseness of methodology and results: We acknowledge the reviewer’s concern regarding the clarity and conciseness of the methodology and results sections. In response, we have thoroughly revised these sections to streamline the narrative, presenting the methodology in a structured format that clearly aligns with the study's phases. The results section has been restructured to focus on key findings and their direct relevance to the study’s objectives, reducing any potential confusion and enhancing readability.

Omission or transfer of results to supplementary material: We carefully considered the suggestion to move certain results to supplementary material. However, after detailed deliberation, we concluded that all the presented results are essential for understanding the study’s conclusions and supporting the main arguments. The current manuscript is, in fact, a highly synthesized version of the primary author's (Oscar Isaac Diez de Bonilla Jiménez) master's thesis. We believe that omitting or transferring these results could compromise the informative integrity of the paper. Each data point contributes crucial context and reinforces the robustness of the findings, ensuring a comprehensive understanding for readers. This justification is provided to support the decision to retain the data within the main text.

Presentation of Study Limitations: We have enhanced the Discussion section by adding a dedicated paragraph that clearly outlines the limitations of the study. This addition provides transparency regarding factors such as the variability of microbial matrices and environmental conditions (e.g., temperature and weather fluctuations) that may influence the applicability of our findings. By addressing these limitations explicitly, we aim to guide readers on the scope of the study's results and encourage cautious interpretation under varying conditions.

Applicability of polynomial correlations (Tables 8 and 9): The reviewer's observation on the limited applicability of polynomial correlations due to differing matrices and external factors is highly valuable. We have revised the manuscript to emphasize that while these correlations offer significant insights within the context of our controlled study, their broader application must be viewed with caution. The text now highlights that other environmental and microbial factors, such as varying weather conditions and temperature, can alter outcomes. This ensures readers are well-informed of the correlations' contextual boundaries.

Alignment with study objectives: We have refined the results presentation to align more closely with the study’s objectives. This involved ensuring that only results that directly support the research aims are included in the main body, avoiding redundancy and enhancing focus. We have also strengthened the connection between the methodology and results by clarifying how each methodological step leads to specific findings and contributes to the study’s overall conclusions.

Comment 2:  Introduction section: Please analyze in more detail the operability of ORP measurements as a tool to capture the effectiveness of disinfection of potable water, since the understanding of underlying mechanisms is crucial, for example, should it be used as single parameter or be used in a set of other parameters? What are the pros and cons? Challenges?

Response 2: 

We appreciate the reviewer’s insightful feedback regarding the need for a more detailed analysis of the operability of ORP (Oxidation-Reduction Potential) measurements in the context of potable water disinfection. In response, we have expanded the Introduction section to address this important aspect comprehensively.

Detailed Analysis of ORP Operability: We have enriched the discussion on how ORP measurements can be utilized as an effective tool for monitoring disinfection processes. This includes a detailed examination of its strengths, such as its ability to provide real-time data and facilitate quick decision-making in treatment processes. Additionally, we have discussed the limitations of using ORP as a single parameter, emphasizing that while ORP is effective for indicating the oxidative potential of a system, its interpretation can be influenced by water matrix characteristics and the presence of other oxidants or reducing agents.

Use as a Single Parameter or in Combination: The revised Introduction now elaborates on whether ORP should be used as a standalone metric or in conjunction with other water quality parameters. We highlight that although ORP is a valuable indicator of disinfection potential, combining it with parameters like chlorine residuals and microbial counts can enhance the reliability and accuracy of water quality assessments. This dual-parameter approach helps to mitigate the limitations of ORP when used independently.

Pros and Cons of ORP: We have added a dedicated subsection outlining the pros and cons of ORP measurements. Pros include its simplicity, rapid feedback, and broad application potential, while cons involve its sensitivity to external variables (e.g., pH, temperature) that can affect readings and potentially lead to misleading conclusions if not properly accounted for.

Challenges in Using ORP: The Introduction now also discusses the challenges faced when using ORP as a monitoring tool, such as calibration requirements, potential interference from complex water chemistries, and the need for operator expertise to interpret the data accurately. These points provide a balanced view of ORP’s practical application in water disinfection processes.

Conclusion on ORP as a Tool: We have integrated these expanded insights to ensure that the Introduction sets a comprehensive stage for the methodology and results that follow, establishing a clear understanding of the context and rationale for choosing ORP as an optimization tool in our study.

Comment 3:   Figure 2 should be amended as it can confuse the reader. For example, Stage 1 follows three independent “paths”, while it seems that there are only two approaches. Please amend the chart in a simpler format to describe the methodology of the study.

Response 3:

We appreciate the reviewer's observation regarding Figure 2 and its potential to confuse readers due to its current complexity. To address this, we have made significant adjustments to the figure to enhance clarity and improve the representation of the methodology.

Revisions to Figure 2: We have simplified the flowchart to accurately depict the three independent “paths” followed in Stage 1, ensuring that it is visually clear and logically structured. The revised figure now distinctly outlines each path while maintaining a straightforward format that highlights the sequential nature of the methodology. This change makes it easier for readers to follow the process and understand the approaches taken in each stage of the study.

Explanation in the Text: To further support the revised figure, we have also updated the accompanying text in the Materials and Methods section to align with the modifications in Figure 2. This ensures consistency and aids in guiding the reader through the methodology with clarity.

Comment 4:   Do you have any indications about Total Coliforms and Enterococci? These are crucial parameters regarding the disinfection of drinking water.

Response 4:

We appreciate the reviewer’s attention to the inclusion of critical microbiological indicators such as Total Coliforms and Enterococci, which are essential in assessing disinfection in potable water. Below, we provide a thorough response to address this concern:

Inclusion of Microbiological Parameters: Our study focused on microbiological parameters that align with the Mexican drinking water quality standards as specified in NOM-127-SSA1-2021. These standards are strictly followed for water quality monitoring and include parameters such as Total Coliforms, which were comprehensively analyzed and discussed in the manuscript. The choice of parameters was based on their regulatory significance and the specific context of water quality assessment in the Cuenca Alto Atoyac region.

Exclusion of Enterococci: We acknowledge the reviewer’s emphasis on Enterococci as an important indicator of fecal contamination and disinfection efficacy. However, this parameter was not included in our study because it does not form part of the mandatory microbiological criteria in the referenced Mexican regulation (NOM-127-SSA1-2021). The decision to exclude Enterococci was guided by the scope of the study and the constraints of available resources and methodologies. Including Enterococci would have required additional laboratory capabilities and financial resources that were beyond the scope and budget of this research project.

Comment 5:   Please provide in addition data about temperature conditions in the sampling points and testing in the lab, as it can also affect the results.

Response 5:

We appreciate the reviewer’s valuable feedback regarding the inclusion of temperature data at the sampling points and during laboratory testing, as temperature can play a significant role in disinfection processes.

Inclusion and Mention of Temperature Data: In response to this comment, we have added temperature data in Tables 1, 2, and 3 to provide detailed information on environmental conditions during sample collection. Additionally, the Introduction has been expanded to highlight the potential influence of temperature on disinfection efficacy.

Clarification in the Methodology: The Materials and Methods section now states: "Temperature conditions at each sampling point were recorded (Table 2), acknowledging their impact on disinfection efficacy. Laboratory tests were conducted at controlled temperatures of 15 ± 4 °C." This ensures that readers are aware of both the field and laboratory conditions.

Results and Correlation Analysis: Although not included in the main text of this manuscript, correlation analyses performed in the primary author’s master's thesis indicated that temperature was not a key influencing factor in this specific case. This insight supports the interpretation of our findings and justifies why temperature was considered but not emphasized as a major determinant in the study.

Experimental Control: In the experimental phase, temperature was controlled to maintain consistency and reliability in laboratory tests, mitigating potential variability.

Comment 6:   Lines 296-299: Lack of knowledge about water distribution features limits the potential to draw safe and justified conclusions. Data regarding point of chlorination, type of disinfectant, real contact time etc should be clearly presented, where possible (e.g. data could be provided in a Table).

Response 6:

We appreciate the reviewer’s insightful comment regarding the inclusion of detailed information on water distribution features, as this is essential for supporting safe and justified conclusions.

Additions to the manuscript: In response, we have included new information in the manuscript based on field observations. Specifically, it has been noted that only five out of the 14 studied sites were actively dosing chlorine: two in the Españita zone (Campamento and Ameca) and three in the Atoyac-Zahuapan zone (Centenario, Allende, and Santo Toribio Xico). Although the exact concentrations of chlorine being applied were not known, we clarified that chlorination aimed to maintain free residual chlorine levels between 0.2 and 1.5 mg/L throughout the distribution network, including at the most remote points, as stipulated by NOM-127-SSA1-2021.

Methodological details: We also specified that monitoring was conducted using printed colorimetric charts as part of the Lovibond Water Testing and Colour Measurement kits. This ensures that readers understand the methods employed to assess chlorine levels in the distribution network and provides context for the disinfection conditions analyzed in the study.

Clarification of limitations: While these additions strengthen the manuscript, we acknowledge that some limitations remain due to the unknown concentrations of applied chlorine at the dosing points. This has been noted in the Discussion section to ensure transparency and guide readers in interpreting the findings with an understanding of the study's constraints.

Comment 7: Figure 3 shows results that are not presented/discussed (e.g. As, Hg etc).

Response 7:

We appreciate the reviewer’s observation regarding Figure 3 and the inclusion of results related to arsenic (As) and mercury (Hg), which were not discussed in the main body of the manuscript.

Clarification of data purpose: The data for arsenic and mercury presented in Figure 3 were not directly measured or analyzed as part of this study. Instead, these parameters were sourced from the Sistema de Información del Agua (SINA) [National Water Information System] of CONAGUA, which is a national-level water quality characterization system in Mexico. These data were included solely as background information to aid in the characterization of groundwater quality and to facilitate the hydrogeochemical zonification of the aquifer. The purpose of including these data was to provide context for the sampling site selection and not for direct analysis in terms of disinfection efficacy.

Description in figure 3: The figure caption specifies the source and purpose of these data: "Figure 3. Geolocation map of the pilot study sampling sites (Table 1). The groundwater quality data (CONAGUA, 2024) is represented by colored circles indicating water quality levels (green: complies with all parameters, yellow: does not comply with some parameters, and red: does not comply with most important parameters)." This ensures that readers understand that these parameters served as a general reference for site selection and the preliminary hydrogeochemical assessment.

Reason for Non-Discussion in Results: Since As and Hg were not part of the direct analysis or core findings related to disinfection processes, they were not further discussed in the Results section. Their inclusion was intended to provide a comprehensive background for the study area rather than contribute to the disinfection-focused results.

We trust that this clarification sufficiently addresses the reviewer’s concern by explaining the role and purpose of the data presented in Figure 3.

Comment 8:  Discussion after clustering (lines 427-464) are general/technical recommendations, without contributing to the aims of the research paper.   Response 8:

We appreciate the reviewer’s feedback highlighting that the discussion following the clustering analysis (lines 427-464) may appear as general or technical recommendations and may not contribute directly to the aims of the research paper.

Revision of the Discussion Section: In response to this comment, we have revised the discussion after the clustering analysis to ensure it is closely aligned with the study’s main objectives. We have refined the text to connect the clustering results more directly with the practical implications for optimizing the disinfection process in the Cuenca Alto Atoyac region. This includes emphasizing how the identified clusters provide insights into water quality variations and inform targeted disinfection strategies.

Removal of General Recommendations: Any content that did not specifically contribute to the interpretation of the results or the research aims has been either revised for clarity or removed to maintain focus. The revised discussion now avoids broad technical recommendations and instead highlights key findings relevant to the practical application of the clustering analysis.

Contribution to Research Aims: We have strengthened the linkage between the clustering analysis and the study’s core objective of optimizing the disinfection process. This ensures that the discussion underscores the relevance of the clustering results and their potential impact on improving water treatment practices in the studied region.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this study, the direct relationship between ORP and residual chlorine concentration after chlorination was evaluated through three three-stage studies to ensure pathogen inactivation in Cuenca Alto Atoyac water sources. However, there are still some shortcomings. Here are specific points that need to be addressed in the revised version:

1.     Repeated descriptions appeared in the discussion section of chemical oxygen demand (COD).

2.     The conclusion mentioned to reduce the formation of disinfection by-products did not see direct evidence in the article.

Author Response

Comment 1: Repeated sescriptions in the discussion section regarding Chemical Oxygen Demand (COD)

Response 1: We acknowledge the reviewer's observation of repeated descriptions related to chemical oxygen demand (COD) in the discussion section. In the revised manuscript, we have carefully reviewed and streamlined the discussion to remove any redundant descriptions of COD. This ensures that the section is concise and focused on key findings without unnecessary repetition. The updated text now presents a clear, direct analysis of COD’s relevance to the study's outcomes without reiterating previously mentioned details.

Comment 2: Lack of direct evidence for the reduction of disinfection by-products (DBP) in the 

Response 2: We appreciate the reviewer’s attention to the conclusions referencing the reduction of disinfection by-products (DBPs). We acknowledge that while the potential for DBP reduction was mentioned as a benefit of ORP-based chlorination strategies, the study did not provide direct evidence for this reduction. In response, we have revised the conclusions to clarify this point. The updated text now states that while the findings support the potential for optimized chlorination to align with best practices that could mitigate DBP formation, direct evidence was not part of this study’s scope. We have also highlighted that future research should address this gap by analyzing the direct impact of ORP-based chlorination on DBP formation.

Revised Conclusion Excerpt: "To ensure optimized disinfection across CAA sources, chlorine doses of 0.3 to 1.5 mg/L and a contact time of 15 minutes were found sufficient to achieve effective pathogen inactivation, as indicated by ORP values between 594 and 687 mV. This strategy ensured microbiological safety in drinking water. While reduced formation of disinfection by-products (DBPs) was noted as a potential advantage, the study did not provide direct evidence for this. Future studies should focus on analyzing DBP formation linked to ORP-based chlorination strategies to substantiate these findings.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been improved, according to comments. Clearer representation of results would better reveal the findings of the study.

Comments on the Quality of English Language

English language could be improved