Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this manuscript, Xavier Parra and colleagues employed an IoT-enabled aeroponic platform controlled by an ESP32 microcontroller and evaluated filtration (40-micron) and ozone-based stabilization (N-Amatic technology). I have following comments:

1, For the title, full name for the abbreviation IoT should be spelt out.

2, For the Abstract, more values should be described. For instance, authors stated that “Results indicate that ozone treatment significantly reduces pathogenic load and odor while enhancing phosphorus availability, though it induces a slight reduction in potassium content.”, but no data were described.

3, For the introduction, more citation should be provided. For instance, Line 42-48 contains no citation. In addition, practical interests of this study should be stated.

4, For the materials and methods, technique replicates and biological replication should be clearly described. Randomization in the samplings should be clearly described. In addition, methods for statistical analysis should be described.

5, For Tables 1, 2, 3, 4, standard error values should be displayed, and results for the significance difference analysis should be included.

6, There is no figure of results in this manuscript. I suggest to present data in Tables 3 and 4 using Figures in the revision.

7, For the discussion section, the unanswered questions in this study and perspectives for future studies should be discussed. In addition, the practical interests of this study should be stressed.

8, Reference should be standardized according to the MDPI template. For instance, the journal name should be in italics.

Author Response

Please find the detailed point-by-point responses to the reviewers' comments in the attached file. These responses clarify the modifications made to the manuscript to address all the concerns raised.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In general, this article is a highly innovative and comprehensive work, in which a significant expansion of the Materials and Methods section was necessary. Overall, the introduction could also be further developed to describe the advantages and limitations of the aeroponic technique in greater detail, and to discuss how this technique may have high potential for future evolution and optimization. I would have preferred the discussion of results to have made use of a greater number of studies and references for a better contextualization of the findings; however, it is recognized that this is possibly such an innovative study that there are still few articles in the literature addressing this specific form of slurry valorization

Introduction

It is suggested to strengthen the Introduction by including additional bibliographic references, particularly in the section dedicated to the aeroponic technique. This would help contextualize its advantages relative to other widely used soilless cultivation techniques, such as hydroponics.

Materials and Methods

a) In Figure 1, define the acronyms SS, FS, and FOS in full. If the image cannot be altered, these definitions should be included in the figure caption.

b) Clarify the sentence presented between lines 138 and 141.

c) Regarding the slurry characterization, the values for electrical conductivity, E. coli, and Salmonella spp. should be included in Table 1. Additionally, the control treatment should be incorporated into this table. Furthermore, in my view, the observed differences between Filtered Slurry (FS) and Filtered-Ozonated Slurry (FOS) do not appear to be significant; it is more plausible that they result from the uncertainty associated with the analytical methods rather than a real effect of the Ozone Purification Technology, as mentioned in lines 146 to 160. How many replicates were performed for the characterization of the different treatments, and what was the standard deviation obtained between the results?

d) Indicate in Table 1 that the characteristic values correspond to the concentrated sample, without the 1/20 dilution in municipal water.

e) Add the values for Cu, Zn, Cd, Pb, and Hg to Table 1, as referred to in lines 161 to 165. Were determinations for Cr and Ni also performed? If so, the respective values should be included; otherwise, their absence should be clarified.

f) For greater clarity, it should be specified between lines 184 and 186 that 8 plants of each species were used, as mentioned in line 95.

g) There is an inconsistency between the text and Table 1: the text justifies acidification citing a 'nitrogen deficiency', yet the data shows a content of 10%. How is this need for reinforcement explained? See lines 210 and 211.

Results

a) In Table 2, the values for EC, pH, and TN for both treatments appear to be similar; it is plausible that the observed differences result from the uncertainty associated with the analytical methods rather than a real effect of the Ozone Purification Technology. How many replicates were performed for the characterization of the different treatments, and what was the standard deviation obtained? Additionally, it is essential to include the E. coli and Salmonella values in the same table.

b) On line 326, correct the unit from 0.16 g/L to 160 mg/L, to maintain consistency with Table 2.

c) Provide a more detailed explanation of why the mineralization process leads to an increase in AP. Additionally, I would like a clearer clarification regarding the decrease in AK in the FOS treatment. Do you consider the difference between 160 and 180 mg/L to be truly significant? The AK concentration in the FOS treatment is only about 10% lower than in the FS treatment, a difference that may fall within the acceptable uncertainty associated with analytical testing. Once again, it is important to state the number of replicates carried out for the quantification of the values presented in Table 2, as well as the respective standard deviation.

d) On line 333, it is stated that ‘while ozonation improves safety’; however, no evidence was presented to support this claim. Could you clarify to what extent ozonation contributes to safety improvement?

e) In Table 3, add the NPK value for the control.

f) In lines 365–368, the attempt to justify the lower values in red leaf lettuce is incomplete, as it omits the impact of the potassium deficiency on the NPK ratio. Given that nutritional imbalance is a known limiting factor, this should be integrated into the discussion of physiological stress.

g) Where is the table presenting the values discussed in chapter ‘3.4. Nutrient Content of Harvested Tissue’?

Conclusions

In the conclusions, it is stated that ozone treatment effectively neutralizes pathogens; however, no evidence is presented throughout the work to support this claim, as the results regarding E. coli and Salmonella were not provided.

Author Response

Please find the detailed point-by-point responses to the reviewers' comments in the attached file. These responses clarify the modifications made to the manuscript to address all the concerns raised.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Authors have addressed each of my previous comments in the revised manuscript.

Author Response

We sincerely thank the reviewer for their time, effort, and highly constructive feedback throughout the review process. We are very pleased that our revisions and explanations have satisfactorily addressed all the concerns raised in the previous round. Your valuable insights, thorough evaluation, and thoughtful suggestions have significantly contributed to improving the clarity, rigor, and overall quality of this manuscript. We deeply appreciate your positive assessment and your support of our work.

Reviewer 2 Report

Comments and Suggestions for Authors

(Reference: Version 2 of the article)

In my view, the work has been substantially improved, being now clearer, more consistent, and methodologically more robust, with a reduction in the previously identified inaccuracies. However, there remain some aspects that should be reviewed and further refined:

a) References should be added on lines 97 and 98. “…and potentially altering the speciation of nutrients to enhance their bioavailability in recirculating systems”.

b) On lines 112 to 116, it might be useful to assess the potential relevance of this treatment for other organic wastes as well, such as sewage sludge or municipal wastewater. Develop this idea, if you agree, further in Chapter 4.5 “Practical Implications and Future Perspectives”.

c) On lines 168 and 169, indicate that the 'ozonated treatment' resulted in a 17% increase in COD compared with the 'filtered treatment.' It seems that the effect of ozone on the final COD is being understated.

d) In the analysis of Table 1, an assessment should be included on whether a concentration of 100 CFU/mL of E. coli is acceptable from a sanitary perspective, as well as specifying for which type of agricultural use this concentration could be considered appropriate. It is suggested that this discussion be integrated between lines 188 and 206. Additionally, Table 1 should clarify whether the presented values for nutrients and heavy metals correspond to the total fraction or the soluble fraction.

e) I consider it important that Table 2 should include the E. coli values, as the undiluted porcine slurry may still pose microbiological contamination risks. Accordingly, it would also be relevant to highlight that these contamination risks are eliminated upon dilution.

f) It is recommended that, on lines 436 and 437, the discussion on microbiological contamination risk be developed more thoroughly, including contextualization of the results in relation to the current legal limits for agricultural application.

g) In the conclusions, specifically in point 4, it should be made explicitly clear whether the obtained E. coli values are acceptable for agricultural use. It is also important to clarify whether these values could be considered high for horticultural crops, particularly those intended for raw consumption, but potentially acceptable for other types of crops. Compliance with applicable legislation, such as that governing livestock effluents, should also be assessed. Greater emphasis should be given to the issue of microbiological contamination, as this represents one of the main limitations associated with the agricultural valorization of porcine slurry.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf