Demonstration of Wastewater Recycling in a Slaughterhouse
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn general, the authors have prepared the manuscript well. It addresses a relevant and current topic, and the methods are clearly written. The manuscript is acceptable for publication in Applied Science, subject to minor revisions.
1)Figure 1: Homogenized the writing style.
2)Line 68: Removed the period after m³ (better to write: m³ d⁻¹).
3)Line 79: Removed the period and wrote COD as a subscript.
4)Lines 98-100: Replaced the numbers with dashes or labels.
5)Homogenized the units consistently throughout the manuscript.
6)Line 104: Numbered the subsection with a number: (2.4.1 Physical Flotation and 2.4.2 Membrane Bioreactor).
7)Line 129: Renumbered as 2.4.3 Reverse Osmosis.
8)Table 2: Corrected the notation to "4000 Chickens d⁻¹" and "8000 Chickens d⁻¹"; removed the comma in the table, Figure 7, and the text for consistency.
9)Applied the same corrections to Table 3, Table 4, Table 5, and Table 7.
Comments on the Quality of English LanguageMinor editing of English language required.
Author Response
Dear Reviewer 1,
Thank you for your thorough review and your kind words regarding our manuscript. We appreciate your constructive feedback and have carefully considered all of your comments. Below, we have provided responses to your suggestions, as well as the corresponding changes made to the manuscript.
Reviewer 1
In general, the authors have prepared the manuscript well. It addresses a relevant and current topic, and the methods are clearly written. The manuscript is acceptable for publication in Applied Science, subject to minor revisions.
Comment 1:
Figure 1: Homogenize the writing style.
Response 1:
Thank you for your suggestion. We have revised Figure 1 and standardized the writing style as recommended.
Comment 2:
Line 68: Remove the period after m³ (better to write: m³ d⁻¹).
Response 2:
Thank you for the suggestion; however, we have decided to keep the period in place, as according to the guidelines of the International System of Units (SI), the use of a period between the terms makes it clearer to read the unit.
Comment 3:
Line 79: Remove the period and write COD as a subscript.
Response 3:
We appreciate your comment, but upon review, we found that COD is already displayed as a subscript.
Comment 4:
Lines 98-100: Replace the numbers with dashes or labels.
Response 4:
We have made the necessary changes and replaced the numbers with dashes or labels as recommended.
Comment 5:
Homogenize the units consistently throughout the manuscript.
Response 5:
The units throughout the manuscript have been homogenized. However, in the Sankey diagram, this was not possible due to software limitations.
Comment 6:
Line 104: Number the subsection with a number: (2.4.1 Physical Flotation and 2.4.2 Membrane Bioreactor).
Response 6:
We have adjusted the subsection numbering as recommended.
Comment 7:
Line 129: Renumber as 2.4.3 Reverse Osmosis.
Response 7:
Thank you for your input. We have renumbered the subsection accordingly.
Comment 8:
Table 2: Correct the notation to "4000 Chickens d⁻¹" and "8000 Chickens d⁻¹"; remove the comma in the table, Figure 7, and the text for consistency.
Response 8:
We appreciate your suggestion, but we have decided to retain the periods and commas. This follows the guidelines of the International System of Units (SI), where the use of periods between terms and commas for thousands enhances readability.
Comment 9:
Apply the same corrections to Table 3, Table 4, Table 5, and Table 7.
Response 9:
As noted above, we have decided to maintain the periods and commas for the same reasons stated in Response 8.
We sincerely appreciate your thorough review and valuable suggestions, which have contributed to improving the quality of the manuscript.
Reviewer 2 Report
Comments and Suggestions for Authors· Lines 30-32: “In the case of slaughterhouse wastewater (SWW) reuse, there are a number of publications on these two phases [6–14], as well as an article on the development phase.” Please, describe some basis of conventional treatments for slaughterhouse wastewater and highlight the novelty of your work.
· Maybe some info about the state of art of the SWW treatment plant before the implementation of new technologies could be moved to the supplementary materials.
· Figure 3: what does dotted line represent? Describe the meanings of different types of lines in the caption.
· If they represent the initial characteristic of SWW, I suggest to move section 3.2 in the Materials and methods.
· It is not very clear for me how the removal rate as been calculated in this work. Pay attention that removal rate must be calculated on “loads” basis and not on “concentration” basis. Was this approach followed? Otherwise, they must be recalculated taking this aspect into account.
Author Response
Dear Reviewer 2,
Thank you for your thorough review and your kind words regarding our manuscript. We appreciate your constructive feedback and have carefully considered all of your comments. Below, we have provided responses to your suggestions, as well as the corresponding changes made to the manuscript.
Comment 1:
Lines 30-32: “In the case of slaughterhouse wastewater (SWW) reuse, there are a number of publications on these two phases [6–14], as well as an article on the development phase.” Please, describe some basis of conventional treatments for slaughterhouse wastewater and highlight the novelty of your work.
Response 1:
Thank you very much for this helpful suggestion. We have added a corresponding section describing conventional treatment methods for slaughterhouse wastewater and highlighted the novelty of our research in comparison to these approaches.
Comment 2:
Maybe some info about the state of art of the SWW treatment plant before the implementation of new technologies could be moved to the supplementary materials.
Response 2:
Thank you for your suggestion. However, as the focus of the article is on the implementation of the recycling system within an existing setup, we consider this section too essential to be moved to the supplementary materials. We believe it is important to keep it in the main text to provide full context for the reader.
Comment 3:
Figure 3: What does the dotted line represent? Please describe the meanings of different types of lines in the caption.
Response 3:
Thank you for pointing this out. We have now added an appropriate explanation to the figure caption to describe the different line types, including the dotted line.
Comment 4:
If they represent the initial characteristic of SWW, I suggest moving section 3.2 to the Materials and Methods.
Response 4:
Thank you for this thoughtful suggestion. We did consider this, but since the table mainly presents concrete results from on-site investigations during plant operation, with the general values only serving as a comparison, we would prefer to keep this section where it currently is.
Comment 5:
It is not very clear for me how the removal rate has been calculated in this work. Please note that the removal rate should be calculated on a “loads” basis and not on a “concentration” basis. Was this approach followed? Otherwise, they should be recalculated taking this aspect into account.
Response 5:
Thank you very much for this important observation. The removal rates provided represent averages over many operational days and were calculated to the best of our knowledge, taking the loads into account. The goal was to give a general assessment of the system’s cleaning performance, rather than specific values for individual days.
We sincerely appreciate your thorough review and valuable suggestions, which have contributed to improving the quality of the manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe article applsci-3195761 evaluated a modification of a wastewater treatment plant (WWTP) to reduce its water demand and obtain reuse water. The work is quite interesting and deserves to be published. However, some improvements are needed.
It is necessary to better clarify what is meant by “indirect discharge”. Treated SWW is most commonly discharged into receiving water bodies or into the municipal sewage network;
The introduction is very succinct. A paragraph on the characteristics and environmental impacts caused by SWW should be added;
The review by Zanol et al. (https://doi.org/10.1016/j.jenvman.2024.120862) addresses several aspects described in this article, including the reuse of treated SWW in agriculture, a practice already adopted in several slaughterhouses in Brazil. I suggest reading and citing this article as a very current reference on this topic;
Line 51: change “volume” to “quantity”;
Lines 65-66: Shouldn’t these figures be in a supplementary material? I am not aware of an appendix in articles;
Figure 3: It is necessary to clarify further whether the only solid waste from the modified WWTP is floated waste and what its destination would be. And what about the destination of solid waste before modification (Figure 2)? It is necessary to include a paragraph discussing these aspects;
Topic 2.5: It is necessary to include the methodologies for determining TSS and ammoniacal nitrogen. In fact, in Zanol et al. (2024), the two main parameters in non-compliance in conventional SWW treatment in Brazil are precisely TSS and ammoniacal nitrogen. It is necessary to give more emphasis to these two parameters in the performance of the modified WWTP;
Topic 2.7: It is necessary to include the Tunisian legislation here (shown in Table 5);
Table 1: include pH and TSS;
Delete Figure 7, as it repeats the data from Table 2;
Table 3: Include data from Zanol et al. 2024 and more characterization parameters;
Line 263: the reduction in N can be attributed to its assimilation by microbial multiplication, as denitrification would hardly occur under the treatment conditions;
Table 5: the other characterization parameters are missing;
COD = 4 mg/L? The detection limit of the method must be considered;
Figure 13: the TS parameter is insignificant. It is more interesting to replace it with TSS data;
Conclusions: Ok.
Author Response
Dear Reviewer 3,
Thank you for your thorough review and your kind words regarding our manuscript. We appreciate your constructive feedback and have carefully considered all of your comments. Below, we have provided responses to your suggestions, as well as the corresponding changes made to the manuscript.
Comment 1:
It is necessary to better clarify what is meant by “indirect discharge.” Treated SWW is most commonly discharged into receiving water bodies or into the municipal sewage network.
Response 1:
Thank you for this valuable comment. This aspect is already addressed in the text at line 86: "Finally, remaining solids are removed in a sedimentation tank, and the overflow is released as an indirect discharge to the sewer and to the municipal wastewater treatment plant." We hope this clarification suffices.
Comment 2:
The introduction is very succinct. A paragraph on the characteristics and environmental impacts caused by SWW should be added.
Response 2:
Thank you for the suggestion. A corresponding section on the characteristics and environmental impacts of slaughterhouse wastewater has been added to enhance the introduction.
Comment 3:
The review by Zanol et al. (https://doi.org/10.1016/j.jenvman.2024.120862) addresses several aspects described in this article, including the reuse of treated SWW in agriculture, a practice already adopted in several slaughterhouses in Brazil. I suggest reading and citing this article as a very current reference on this topic.
Response 3:
Should the authors of the aforementioned article absolutely need a citation in order to increase the visibility of their work, we would like to give them this opportunity.
Comment 4:
Line 51: Change “volume” to “quantity.”
Response 4:
Thank you for pointing this out. The term "volume" has been changed to "quantity" accordingly.
Comment 5:
Lines 65-66: Shouldn’t these figures be in supplementary material? I am not aware of an appendix in articles.
Response 5:
Thank you for the suggestion, as the pictures are too large for the text, but give a very good idea of the situation on site, we have decided to leave them attached.
Comment 6:
Figure 3: It is necessary to clarify further whether the only solid waste from the modified WWTP is floated waste and what its destination would be. And what about the destination of solid waste before modification (Figure 2)? It is necessary to include a paragraph discussing these aspects.
Response 6:
Thank you for the comment. As described in section "2.4.2 Membrane Bioreactor," excess sludge is removed as flotation waste. A paragraph explaining the destination of the solid waste before and after modification has been added.
Comment 7:
Topic 2.5: It is necessary to include the methodologies for determining TSS and ammoniacal nitrogen. In fact, in Zanol et al. (2024), the two main parameters in non-compliance in conventional SWW treatment in Brazil are precisely TSS and ammoniacal nitrogen. It is necessary to give more emphasis to these two parameters in the performance of the modified WWTP.
Response 7:
We appreciate this suggestion. We have now added a section describing the methodology for TSS measurement. The measurement of ammonium was already included and performed using ion chromatography, as previously stated.
Comment 8:
Topic 2.7: It is necessary to include the Tunisian legislation here (shown in Table 5).
Response 8:
Thank you for pointing that out. Tunisian legislation has now been added to the relevant section.
Comment 9:
Table 1: Include pH and TSS.
Response 9:
The pH and TSS values have now been included in Table 1.
Comment 10:
Delete Figure 7, as it repeats the data from Table 2.
Response 10:
We understand your concern, but we believe that the visual representation in Figure 7 provides an additional layer of clarity and helps readers understand the breakdown of the data. Therefore, we would prefer to retain the figure.
Comment 11:
Table 3: Include data from Zanol et al. 2024 and more characterization parameters.
Response 11:
Thank you for the suggestion. While we appreciate the relevance of the Zanol et al. data, we feel that the current data provided are sufficient for our focus on poultry slaughterhouses, which differs slightly from the broader scope of the Zanol et al. study.
Comment 12:
Line 263: The reduction in N can be attributed to its assimilation by microbial multiplication, as denitrification would hardly occur under the treatment conditions.
Response 12:
Thank you for this observation. However, since no further biomass was produced after day 60, and no excess sludge was removed, we believe that the nitrogen removal observed after this period was due to biological nitrogen removal rather than biomass assimilation.
Comment 13:
Table 5: The other characterization parameters are missing.
Response 13:
We have included the most relevant parameters for this study. Unfortunately, due to the remote location of the site, some biological measurements could not be performed. However, the main focus of this work remains on the technical implementation of the processes.
Comment 14:
COD = 4 mg/L? The detection limit of the method must be considered.
Response 14:
As mentioned in the Materials and Methods section, the COD measurements were performed using the "QuickCODlab-03D0318 from LAR Process Analysers AG (Berlin, Germany) via a thermal disintegration process." This method has a detection limit of 0.5 mg/L, and thus, the reported value is accurate.
Comment 15:
Figure 13: The TS parameter is insignificant. It is more interesting to replace it with TSS data.
Response 15:
We agree that TSS is an important parameter. However, in this context, most TSS is already removed via flotation, and by the time the MBR is in operation, the TSS is effectively zero by definition. Since TSS can be derived from the TS and TDS data (which are related to conductivity), we believe that using TS and conductivity in this diagram provides more comprehensive information.
We greatly appreciate your valuable feedback and have made the suggested revisions where appropriate.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThank you for the improvements of the paper. In my opinion, it can now be accepted for publication.
Reviewer 3 Report
Comments and Suggestions for AuthorsIn the article applsci-3195761, the modification of a wastewater treatment plant (WWTP) was evaluated to reduce its water demand and obtain reused water. This second version is better, as the authors have made most of the suggested/necessary changes. The work is quite interesting and deserves to be published in this prestigious journal.
