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Peer-Review Record

Biofilter, Ventilation, and Bedding Effects on Air Quality in Swine Confinement Systems

AgriEngineering 2025, 7(3), 73; https://doi.org/10.3390/agriengineering7030073

by Hong-Lim Choi^1,2,*, Andi Febrisiantosa^1,3, Anriansyah Renggaman^1,4

, Sartika Indah Amalia Sudiarto^1,4, Chan Nyeong Yun⁵ and Arumuganainar Suresh^2,6

Reviewer 1: Anonymous

Reviewer 2: Anonymous

AgriEngineering 2025, 7(3), 73; https://doi.org/10.3390/agriengineering7030073

Submission received: 29 December 2024 / Revised: 25 February 2025 / Accepted: 28 February 2025 / Published: 7 March 2025

(This article belongs to the Special Issue Innovations, Engineering, Technologies and Best Practices for Ensuring Work Safety in Agriculture)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

see attached

Comments for author File: Comments.pdf

Author Response

RESPONSE TO REVIEWER 1

Comments 1. The manuscript discusses a study exploring three approaches to controlling emissions of bacteria, VOC, H2S, and NH3. While the cost of such a study was likely high, the lack of error analysis and lack of replication limits the utility of the results.

Response: We agree with the reviewers' comments regarding the cost associated with the engineering works in this study. However, we would like to emphasize that the significant reduction in odor and particulate matter achieved by our modified design house demonstrates the effectiveness of our approach. For the reviewers' reference, we conducted replicated sample analyses and initially included average data in the manuscript. In the revised version, we have now included both the average data and the standard deviation to provide a more comprehensive representation of the results. Please refer to the revised manuscript for these updates.

Comments 2. There are no details as to measurement methodologies. Were isokinetic orifices used? Where were the samples collected? How was the variation in flow across the outlets (presuming the measurements were made there) addressed? Were measurements replicated? Were field blanks conducted? Were calibration gasses/solutions used? What corrections were made for differing environmental conditions?

Response: We acknowledge that the initial submission lacked some details in the Materials and Methods section due to the tight submission deadline. In the revised manuscript, we have expanded this section to include all necessary details, ensuring the reliability and reproducibility of our study. Specifically, we have clarified that samples were collected at a height of 1.5 meters from the floor, and the flow rate was maintained consistently across all houses. Since all three houses were located in the same premises, there were no significant environmental variations during the experiment, and thus no corrections were required. Field blanks and calibration gases were not used in this study. Additionally, we have included the standard deviation for replicated measurements in the revised manuscript. Please refer to the updated Materials and Methods section for these details.

Comments 3. There is a lack of measurement error analysis. The statistical analysis assumes that every measurement is error-free. lack of replication severely limits the usefulness of the study results. I do not see any methodologies confirming the accuracy of any measurements. Protocol of Kumari (Li 130) is too vague since he appears to have used other analyzers than used here. The Gastec probes (Li 138) apparently have errors of around 25% of tube concentration range. The lack of information as to errors of the probes in this study is problematic: a 25% error in GasTec measurements appears to exceed the reported ‘significant differences’ between the treatments. The errors in the GS/MS measurements are not stated so it is not possible to evaluate the results. NH3 measurements typically have wall adsorption issues- how was this addressed?

Response: For the reviewers' reference, we collected three samples for each analysis and processed them separately. The initial manuscript presented average data, but the revised version now includes the standard deviation for all data points. The protocol used for volatile fatty acid (VFA) and volatile organic acid (VOA) analysis, as described by Kumari et al., was strictly followed for GC/MS sample collection, storage, injection volumes, and analysis methods.

Regarding the use of GasTec probes for NH₃ and H₂S analysis, we acknowledge the reviewers' concern about the potential 25% error associated with this method. While GasTec probes may not provide the same level of accuracy as gas chromatography, they still offer comparable data for specific gas samples. In the revised manuscript, we have included standard errors for triplicate analyses to enhance the reliability of the data. Please refer to the revised tables and figures for these updates.

Comments 4. The significant digits presented throughout the ms. suggest unbelievable accuracies of 0.001 ppb in VOC and 0.01 for H2S and NH3. Care needs to be taken to match the significant digits to the measurement errors.

Response: We fully agree with the reviewers' comments on the importance of data accuracy, particularly at the ppb level. In our analysis, sample peak values were compared with standard graph peak values, and decimal data were reported. In the revised manuscript, we have adjusted the significant digits to align with the measurement errors, ensuring greater precision and transparency. Please refer to the revised manuscript for these changes.

Comments 5. There are many words with hyphens that do not fall at the end of sentences.

Response: The manuscript has been revised to address all the reviewers' comments, including reducing redundancy and improving clarity. Please see the revised manuscript for the updated content.

Specific issues follow:

Comments 6. Li 2: while ‘environmental sustainability’ is a hot topic, I do not see further discussion of this. It should be removed.

Response: Yes, authors agree that we we did not discussed in details on “environmental sustainability”, of this study. The manuscript is revised accordingly. Please see the abstract, Li. 2

Comments 7. Li 22: distinction needs to be made that these are not ‘models’ (implied theoretical). Please rephrase here and elsewhere.

Response: We appreciate this suggestion and have implemented the recommended changes in the revised manuscript.

Comments 8. Li 58: ‘emit’ not ‘expel’, Li 81-83: move to first paragraph

Response: The text has been revised to improve clarity.

Comments 9. Li 90-92: refence these figures and table with separate sentences.

Response: The manuscript has been modified according to the reviewer's suggestion.

Comments 10. Figure 1: should show where samples were collected

Response: Figure 1 on page 4 has been updated to include the sample collection points.

Comments 11. Figure 1: should show where samples were collected and Figure 2: Much more explanation in the text is needed.

Response: Sample collection points have been marked in Figure 1, and additional explanations for Figures 1 and 2 have been provided (see page 2 and Table 1)."

Comments 12. Li 167-181: What is the cause of the peaks in NH3 in M1?

Response: We also observed unexpected NH3 peaks in M1 during initial stages, likely due to filter orientation. Our findings suggest horizontal filter positioning is more effective than vertical positioning for removing gaseous compounds. This explanation has been added to the manuscript.

Comments 13. Figure 4, 5: Use more distinctly different symbols

Response: Figures 4 and 5 have been revised according to the reviewers' suggestions. Please see page 8.

Comments 14. Li 172, 180, 186: state the results from these papers so the terms ‘align with’, consistent with’, and ’relate’ have meaning. How closely do they match? What matches?

Response: Following the reviewers' recommendation, we have incorporated and discussed comparative data from previous studies alongside our current findings to provide readers with a more comprehensive understanding

Comments 15. Li 176: ‘This suggest that…’ Li 181: new paragraph for H2S. Li 198-99: belongs in introduction, Li 239-242. Belongs in ‘Introduction’.

Response: The manuscript has been revised accordingly.

Comments 16. Li 214: H2S not ‘sulfuric’

Response: We would like to clarify that 'sulfuric' in this context refers to sulfuric compounds such as Dimethyl sulfide and Dimethyl disulfide, not H2S.

Comments 17. Table 2: what are the units? The notes indicate Mean+/- standard deviations and significant differences are presented. Where?

Response: We apologize for the oversight in Table 2. The revised manuscript now includes mean values with standard deviations (see page 10)."

Comments 18. Li 242-244. Rephrase. The study included bacterial measurements. Again, significance needs to include measurement errors.

Response: We acknowledge this point and have updated the manuscript to include standard deviations for our triplicate measurements, rather than just average values.

Comments 19. Li 210, 246-47: tense wrong.

Response: All tense inconsistencies have been corrected in the revised manuscript.

Comments 20. Conclusions: This study is not ‘comprehensive’ as it has not replication. Consequently, conclusions need to be phrased with less confidence.

Response: The conclusion section has been revised as suggested (see page 12).

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript "Ventilation and Bedding Effects on Air Quality in Swine Confinement Systems" (agriengineering-3426122). Upon reviewing the manuscript, I noted that the authors failed to present any novelty in the study. Additionally, the structure of the manuscript, particularly the Materials and Methods and Results and Discussion sections, lacks scientific robustness (in terms of content and writing). Combined, these two sections contain only six paragraphs, raising questions about the solidity of the work. The authors need to explore the results and discussion more thoroughly and provide stronger methodological foundations. As major observations, which must be attended to, I highlight:

1 – I noticed some grammatical errors in writing; therefore, I suggest a revision of the English by a native speaker.

2 – Authors must reformulate the abstract. Note that you are presenting an abstract with 249 words, while AgriEngineering limits abstracts to 200 words. I also emphasize that authors must follow the principle of presenting the study's key findings in the abstract, which is not evident in this version.

3 – The study does not present a novel or innovative scientific contribution. The practices analyzed (ventilation and bedding systems in swine facilities) have been extensively covered in the existing literature. The combination of ventilation and bedding materials is a common approach in swine management studies. There is no methodological or theoretical advancement over the previously cited studies.

4 – The Materials and Methods section lacks critical detail to ensure replicability and robustness:

· There is insufficient justification for the choices of ventilation systems and bedding types (e.g., sawdust, biochar).

· The selection criteria for these systems are not clearly explained.

· The number of pigs and the experimental conditions are limited, which constrains the broader generalizability of the findings.

5 – The Results and Discussion sections are notably brief, comprising only three paragraphs in total. There is minimal exploration of the results beyond basic data descriptions:

· The implications of the findings are not deeply discussed.

· There are no critical comparisons with similar studies.

· There is a lack of analysis regarding the cost-benefit relationship of the different approaches and their practical implementation in real-world systems.

Comments on the Quality of English Language

The grammar of the writing of the work needs to be revised.

Author Response

RESPONSE TO REVIEWER 2

Comments 1. I noticed some grammatical errors in writing; therefore, I suggest a revision of the English by a native speaker.

Response: As per reviewers suggestions, The manuscript has been professionally edited by a native English speaker., please check the revised manuscript.

Comments 2. Authors must reformulate the abstract. Note that you are presenting an abstract with 249 words, while AgriEngineering limits abstracts to 200 words. I also emphasize that authors must follow the principle of presenting the study's key findings in the abstract, which is not evident in this version.

Response: We sincerely thank the reviewers for highlighting the word limit requirement for the abstract in AgriEngineering. In response to this feedback, we have reformulated the abstract to adhere to the specified word limit while ensuring that the key findings of the study are clearly presented. Please refer to the revised abstract section for these changes.

Comments 3. The study does not present a novel or innovative scientific contribution. The practices analyzed (ventilation and bedding systems in swine facilities) have been extensively covered in the existing literature. The combination of ventilation and bedding materials is a common approach in swine management studies. There is no methodological or theoretical advancement over the previously cited studies.

Response: We acknowledge the reviewers' observation that ventilation and bedding systems in swine facilities have been extensively studied for odor reduction. However, this study introduces an innovative approach by modifying the biofilter pad system (vertical and horizontal configurations) and incorporating the recirculation of treated swine wastewater effluent to enhance odor reduction in swine confinement facilities. The revised manuscript emphasizes this novel scientific approach and its implications for odor control. Please refer to the updated manuscript for a detailed discussion of these modifications.

Comments 4. The Materials and Methods section lacks critical detail to ensure replicability and robustness:

There is insufficient justification for the choices of ventilation systems and bedding types (e.g., sawdust, biochar).
The selection criteria for these systems are not clearly explained.
The number of pigs and the experimental conditions are limited, which constrains the broader generalizability of the findings.

Response: We agree with the reviewers that the initial submission lacked some details in the Materials and Methods section due to the tight submission deadline. In the revised manuscript, we have expanded this section to include all necessary details, ensuring the reliability and reproducibility of our study. Additionally, we have provided a thorough justification for the selection of bedding materials and the ventilation systems employed. Please refer to the revised Materials and Methods section for these updates.

Regarding the number of pigs used in the study, we acknowledge that the sample size was limited. However, we believe that the results still provide valuable insights and suggest meaningful conclusions that can inform future research and practical applications.

Comments 5. The Results and Discussion sections are notably brief, comprising only three paragraphs in total. There is minimal exploration of the results beyond basic data descriptions:

The implications of the findings are not deeply discussed.
There are no critical comparisons with similar studies.
There is a lack of analysis regarding the cost-benefit relationship of the different approaches and their practical implementation in real-world systems.

Response: We appreciate the reviewers' feedback on the Results and Discussion section. In the revised manuscript, we have conducted a deeper analysis of the results and expanded the discussion to include more relevant studies and comparisons. This enhancement provides a more comprehensive understanding of the findings and their implications. Please refer to the revised Results and Discussion section for these improvements.

We also acknowledge the importance of cost-benefit analysis for practical applications. While this study did not include a cost-benefit analysis, we recognize its significance and plan to address this aspect in our future research.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

See attached document

Comments for author File: Comments.docx

Author Response

Reviewer 1 comments to author RESPONSES of original manuscript

Comments in Red

Response in Blue

I do not see any standard deviation information added.

Response: We kindly request the reviewers to refer to the revised manuscript, which now includes the mean ± standard deviation (SD) of three replicate analyses for all relevant data. Please see Figure 3, Figure 4, and Table 2 for the updated results.

Given the building proximity to tree cover in Fig 2, there was certainly different air flow at the exhaust and intakes and heating of the walls and roof. External air flow then influences the fan efficiency which influences the dilution in the building. Also, the sample locations indicated certainly had very difference environmental conditions given differing air circulations even if the three buildings had identical external exposures. Air flow (direction and speed throughout the building at least differed, which likely also influenced humidity and temperature at a given point. These factors all need to be considered and their influence discussed. Also lack of isokinetic sampling prevents the direct comparison of the samples.

Response: We acknowledge the reviewer’s concern regarding the potential influence of external airflow on the internal environment of the experimental swine houses. However, in our design, the exhaust fan is equipped with a movable slit, which minimizes the impact of external airflow on the internal conditions. Additionally, all three houses are located in the same premises, and samples were collected simultaneously each day between 1:00 PM and 2:00 PM during the experimental period. Temperature and humidity were monitored, but no significant variations were observed among the houses. As the variations were negligible, temperature and humidity data were not included in the manuscript.

While the procedure is indicated, the accuracy depends on the analysis of standards, neither indicated in the Kumari et al. paper in support of the method or here in support of the use of the method in this situation and analytical skills of the analyst. What is the accuracy?

A 5-min sample is not very indicative of the variation over the 24 hr day. The concentration most likely varied over the day as fresh waste production varies and temperature/humidity varies. This should have been assessed. Were measurements taken at the same time each day? When?

Response: The revised manuscript now includes detailed information on the use of standard curves for each chemical analyzed. This addition provides clarity on the methods used. Please refer to Page 5 for the updated methodology.

We agree that sampling for 5 minutes out of 24 hours may not fully represent the entire day. However, we followed a consistent sampling protocol (1:00 PM–2:00 PM daily) based on the method described by Kumari et al. (2016). While this approach may not capture diurnal variations, it ensures consistency across all samples. Furthermore, the close proximity of the three houses ensured that any temperature or humidity changes affected all houses equally, with no significant differences observed among them.

When GasTec says +/-25%, that is based on sampling of the same concentration by multiple samplers. So the samples are comparable +/- 25%. The error bars in Fig 3. and 4 do not represent these large, at least, 25% errors.

Response: Figure 3 and Figure 4 have been revised to include standard deviation values derived from replicate analyses. Please refer to Page 8 for the updated figures.

Good that significant digits have been addressed to some degree. But you did not use a standard, so your standard peak is purely hypothetical. If you consider the errors of measurements, I suspect you still are reporting digits that are not valid (eg 5.94 ppm NH3 +/-25% if tube was maximum range of 10 ppm then you should report 5.9 +/- 2.5 ppm).

Response: We confirm that the Gastec probes were used within their expiration date and were pre-calibrated for immediate use. However, we acknowledge that the error margin is higher (25%) at low concentrations. The manuscript has been revised to reflect this limitation, as suggested by the reviewers.

I do not see changes in the comparison statistics or presentation of statistical significance that would suggest consideration of the accuracy of measurements has been included. Your Standard deviation values is a precision measure, not an accuracy measure.

Response: We agree that the original manuscript included excessive decimal points in the data. The revised manuscript has been updated to reduce the number of decimal points, ensuring greater accuracy and readability.

Comments 5. There are many words with hyphens that do not fall at the end of sentences.

Response: The manuscript has been revised to address all the reviewers' comments, including reducing redundancy and improving clarity. Please see the revised manuscript for the updated content.

Good

Comments 6. Li 2: while ‘environmental sustainability’ is a hot topic, I do not see further discussion of this. It should be removed.

Response: Yes, authors agree that we we did not discussed in details on “environmental sustainability”, of this study. The manuscript is revised accordingly. Please see the abstract, Li. 2

Good

Comments 7. Li 22: distinction needs to be made that these are not ‘models’ (implied theoretical). Please rephrase here and elsewhere.

Response: We appreciate this suggestion and have implemented the recommended changes in the revised manuscript.

Good

Comments 8. Li 58: ‘emit’ not ‘expel’, Li 81-83: move to first paragraph

Response: The text has been revised to improve clarity.

Comments 9. Li 90-92: refence these figures and table with separate sentences.

Response: The manuscript has been modified according to the reviewer's suggestion.

Comments 10. Figure 1: should show where samples were collected

Response: Figure 1 on page 4 has been updated to include the sample collection points.

Comments 11. Figure 1: should show where samples were collected and Figure 2: Much more explanation in the text is needed.

Response: Sample collection points have been marked in Figure 1, and additional explanations for Figures 1 and 2 have been provided (see page 2 and Table 1)."

Information on the time of measurement needed. See above for time of day influences.

Response: The revised manuscript now explicitly states that samples were collected daily between 1:00 PM and 2:00 PM. This information has been added to the Materials and Methods section for clarity.

Comments 12. Li 167-181: What is the cause of the peaks in NH3 in M1?

I do not see thus explanation in the manuscript. Influence of filter orientation shows you that your sampling error was significant.

Response: The term "filter" refers to the biofilter used in the exhaust system, which has both vertical and horizontal orientations. The horizontal orientation was found to be more effective at removing gaseous compounds compared to the vertical orientation. This is not a sampling error but a design feature. The manuscript has been revised to include a clearer explanation of this aspect. Please see Page 7 for the updated discussion.

Comments 13. Figure 4, 5: Use more distinctly different symbols

Response: Figures 4 and 5 have been revised according to the reviewers' suggestions. Please see page 8.

Comments 14. Li 172, 180, 186: state the results from these papers so the terms ‘align with’, consistent with’, and ’relate’ have meaning. How closely do they match? What matches?

I do not see this change

Response: The revised manuscript now includes a more discussion comparing our findings with those of other related studies. Please refer to the Results and Discussion section for the updated content.

Comments 15. Li 176: ‘This suggest that…’ Li 181: new paragraph for H2S. Li 198-99: belongs in introduction, Li 239-242. Belongs in ‘Introduction’.

Response: The manuscript has been revised accordingly.

Comments 16. Li 214: H2S not ‘sulfuric’

Response: We would like to clarify that 'sulfuric' in this context refers to sulfuric compounds such as Dimethyl sulfide and Dimethyl disulfide, not H2S.

Sulfurous is a better term. Does not indicate a bond state.

Response: Yes, sulfurous is the correct words, the manuscript revised accordingly. Please see page no. 5.

Comments 17. Table 2: what are the units? The notes indicate Mean+/- standard deviations and significant differences are presented. Where?

Response: We apologize for the oversight in Table 2. The revised manuscript now includes mean values with standard deviations (see page 10)."

Comments 18. Li 242-244. Rephrase. The study included bacterial measurements. Again, significance needs to include measurement errors.

Response: We acknowledge this point and have updated the manuscript to include standard deviations for our triplicate measurements, rather than just average values.

The Standard deviations of the triplicate sample is a precision measure, not an accuracy measure.

Response: We have included the standard deviation values for the relevant data in the revised manuscript. However, we are unsure how to address the specific query raised by the reviewer. We hope the provided standard deviation data clarifies the reproducibility and variability of our results.

Day	M1			M2			M3
Day	TBC	TE	TC	TBC	TE	TC	TBC	TE	TC
35	592	478	3	796	470	13	1200	218	314
42	1002	550	11	872	403	41	1692	425	198
49	1412	622	18	948	336	68	2184	632	82
59	1024	930	152	856	552	50.5	1924	634	122
66	1192	714	128	1204	536	93.3	2266	752	290
73	1360	698	104	1552	520	136	2608	870	458
80	1150	479	93	1624	414	108	2476	977	466
87	940	260	82	1696	308	80	2344	1084	474
94	480	260	50	588	196	41	1912	266	88
101	882	356.5	266.5	869	297	99.3	2200	465.5	172
108	1284	453	483	1150	398	158	2488	665	256
Average	1028.9	527.3	126.4	1105.0	402.7	80.7	2117.6	635.3	265.5
SD	297.5	204.5	140.4	372.8	112.2	43.7	411.5	277.7	149.3

		total bacterial count (TBC)	Total E.coli (TE)	Total coliforms (TC)
	M1	1028.9	527.3	126.4
	M2	1105	402.7	80.7
	M3	2117.6	635.3	265.5

Comments 19. Li 210, 246-47: tense wrong.

Response: All tense inconsistencies have been corrected in the revised manuscript.

Comments 20. Conclusions: This study is not ‘comprehensive’ as it has not replication. Consequently, conclusions need to be phrased with less confidence.

Response: The conclusion section has been revised as suggested (see page 12)

We sincerely thank the reviewers for their valuable feedback, which has significantly improved the quality and clarity of our manuscript. We hope the revisions address all concerns adequately. Please let us know if any additional changes are required.

Reviewer 2 Report

Comments and Suggestions for Authors

Considering all the reviews provided by the authors, I am considering this manuscript for publication.

Author Response

Thank you for your positive consideration of the manuscript. I appreciate the time and effort you have dedicated to reviewing the work, which has significantly improved the quality and clarity of our manuscript.

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

See attached file

Author Response

Reviewer 1 comments to author RESPONSES of original manuscript

Rev 2 Comments underlined and Red

Response: underlined and Blue

I do not see any standard deviation information added.

Comment: Good. The error bars should be 25% of tube maximum concentration range, not 25% of the value. Combine your errors as sqrt(error1+error2). So M3 data values of non-detects should also have error bars they are not zero values.

Response : We appreciate the reviewer's clarification regarding the calculation of error bars. We have revised the methodology to ensure that the error bars now represent 25% of the tube maximum concentration range, as suggested.

We thank the reviewer for pointing out this oversight. We have now included error bars for the M3 data values corresponding to non-detects. Please see the Figure 3 and 4.

Comment: Good. Include the temperature and humidity measurements (with where they were taken in Fig 1 or 2). But solar radiation is certainly different between houses. If not measurements were made, you need to state that you ‘assumed’ that the environments were identical unless measured.

Response:

We appreciate the reviewer’s insightful comment regarding the environmental measurements.

We have now included the temperature and humidity measurements (mean ± SD) in the revised manuscript. These measurements were taken at the center of each animal house where samples were taken, and have been added to Figure 1 to provide a clear visual representation of the environmental conditions. Please see the figure 1, and material and method section. Herewith We provided the temperature and humidity data on the three houses, which was showing minimal differences among houses.

Solar Radiation Differences:

The reviewer is correct that solar radiation may differ between houses. Unfortunately, solar radiation was not measured during the study. To address this, we have explicitly stated in the revised manuscript that we assumed the solar radiation conditions were identical across the houses unless otherwise measured. This clarification has been added to the Methods to ensure transparency. Please see the materials and method section.

Comment: This is good. Do you have multiple measurements of the standard gases? That would give you an accuracy of the VOC GC measurements- which if available should be added to the errors indicated in Table 2. Combine your errors as sqrt(error1+error2).

Response:

We appreciate the reviewer’s suggestion to improve the accuracy and error reporting of the VOC GC measurements. Unfortunately, we do not have multiple measurements of the standard gases for this study. we have ensured that the existing errors in Table 2 are calculated using the standard deviation of the replicate analysis.

Response: Figure 3 and Figure 4 have been revised to include standard deviation values derived from replicate analyses. Please refer to Page 8 for the updated figures.

Comment: M3 data values should also have error bars as indicated in Comment 1 above.

Response: We thank the reviewer for pointing out this oversight. We have now included error bars for the M3 data values corresponding to non-detects. Please the Figure 3, page no.8

Comment: OK