Evaluation of TiO₂ Based Photocatalytic Treatment of Odor and Gaseous Emissions from Swine Manure with UV-A and UV-C

Round 1

Reviewer 1 Report

This work entitled "The Evaluation of TiO2 Based Photocatalytic Treatment of Odor and Gaseous Emissions From Swine Manure With UV-A and UV-C" examines scalability of TiO2-based photocatalysis treatment with UV-A and UV-C light to pilot-scale conditions. The paper can be acceptable for publication after major revise.

• The introduction is well written. However, I suggest that authors include a separate paragraph at the end of the introduction explaining the significance of the work as well as objectives. This could be also added to the abstract section.
• Please provide a table of abbreviations as there is a lot of terms abbreviated throughout the text.
• Conclusion section appears to be just a detailed summary of results/observations. All conclusions must be convincing statements on what was found to be novel, impactful based on strong support of the data/results/discussion. Conclusions must improve, Original and unique contribution explicit in and quantified the Conclusions (this should not be another Abstract).
• Results and discussion part is basically more results. I would suggest that the authors compare their results with recent publications in the field and enhance the number of references. This would add value to this work.
• To what extent this approach is feasible to implement in other types of barns (cattle barns, chicken barns) and if so, does it need huge modification? Perhaps it could be addressed in the conclusion section.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript evaluated the photocatalytic UV-A/UV-C effect on odor, VOCs, ammonia, GHG, ozone ecc from swine manure.The application of UV-A, UV-C with different wavelength, UV dose and light intensity was tested.

The topic is extremely interesting, for the importance to reduce pollutants originated and emitted from confinements, storage sites and fertilized soil in livestock farming.

The manuscript was well designed and clearly presented. 

An important result is that N2O, with the highest global warming potential among the considered GHG, was mitigated significantly (from 8 to 25%) almost for all treatments (not for 367 nm). Good the economic analysis for the treatments application to livestock buildings.

Observations:

At L 59 correct the citations : "...pioneered UV-A photocatalysis in swine weaning and farrowing units reporting mitigation of NH3, GHGs, particulate matter (PM)…."

Line 94 Please correct the dimensions of the chambers (0.53 m, as reported in the scheme of Figure 2)

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The work of dr. Myeongseong Lee et al. aimed to evaluate the photocatalytic UV treatment of gaseous emissions of odor, odorous volatile organic compounds (VOCs), ammonia (NH3), and other gases  (greenhouse gases (GHGs), O3 – sometimes considered as by-products of UV treatment) from stored swine manure on  a pilot-scale because they have detrimental effects on the quality of life in rural communities, the environment, and climate.

The manure emissions were treated in fast-moving air using a mobile lab equipped with UV-A and UV-C lights and TiO2-based photocatalyst. Treated gas airflow (0.25 to 0.76 m3∙s−1)  simulates output from a small ventilation fan in a barn. Through controlling the light intensity and airflow, UV dose was tested also from the  techno-economic point of view.

They have shown that the treatment effectiveness depended on the UV dose and wavelength. The proposed technology UV technology was sufficiently effective in treating odorous gases, and the mobile lab is ready for farm-scale trials. The UV technology can be considered for the scaled-up treatment of emissions and air quality improvement inside livestock barns.

Author Response

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Author Response File: Author Response.docx

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Below are line by line comments followed by general comments:

Line 67: the word data should be used in a pleural context

Line 80: Biochar is actually produced in pyrolysis. Little pyrolysis occurs in torrefaction. Please address this.

Line 101: Fix the unit. gal = gallon and not gall

Section 2.1 Materials: How was the biochar prepared and processed after it was produced? This information would be useful to others as biochar properties are strongly influenced by production conditions and post treatment.

Tables 1 & 2, Figure 3, and relevant discussion: It is surprising to see that control H2S emission varied significantly by an order of magnitude, suggesting that the experimental conditions may not have been consistent. Were all experiments conducted at the same time or were control and two rates of biochar were evaluated in, then this was repeated later? A significant lab or day effect seems present in these data. In Figure 3, the images of the manure buckets seem to show a fine textured biochar. Which biochar is this? The corn stover biochar should be relatively fine textured, where as the red oak biochar may have larger particles, based on the feedstock. Please label this in the figure.

Table 5: time spend or spent in the column of data labels?

General comments: The objective of this study was to evaluate the potential of biochar to reduce ammonia and hydrogen sulfide emission during agitation of liquid manure because emission during agitation poses health risks to workers and generally adds toxin to air which can harm others and also reduce air quality. While this study has relevance to the journal and is an important contribution to society, the experimental design, which was intended to be pilot scale, has no relevance to field conditions. Specifically, it takes about two hours to stir a 1200 head swine barn pit, prior to pumping. Conventional equipment consists of a series of at least two chopper pumps which are lowered through a vent at the edge of the building. Indeed, maximal release of gases occurs with the onset of stirring, however the three minute agitation in this study, which rapidly stirred the small volume may not have relevance to field applications.

Clumping of wetted biochar was attributed to the decreased performance of the high application rate. How do the authors suggest applying a film of biochar to manure in a pit and how can pelletized biochar, which the authors suggest may provide for safer handling, stay afloat? Only in the first few (< 5) minutes after application was the reduction of gas emissions significant with biochar application, however in a field application, it takes much longer to fluidize and stir the manure. No information was provided on how the biochar was produced. Perhaps biochar produced at higher temperatures which would be more hydrophobic and carry greater ammonia and hydrogen sulfide adsorption capacity may be more resistant to wetting and, hence, aggregation, followed by settling? It would be nice to see a more thorough statistical analysis. Specifically, a rate correlation analysis over time to determine the length time after application during which biochar significantly reduced gas emission. Figures in the appendix suggest non-linear model comparisons. There are many undefined acronyms throughout the manuscript and while the writing is fairly clear to understand, there are some poorly phrased passages and some assumptions such as the ‘excellent potential to save people and livestock’ by using biochar as a film over manure. The concept is great and warrants effective and pragmatic investigation under field relevant conditions, however the design was far from field relevant. Many of the grammatical errors outlined in the line-by-line comments above suggest that some of the authors including JK and RCB who are full professors with native English may likely never have even reviewed the manuscript. Finally, the significant and substantial difference in control emissions presented in Tables 1 and 2 are alarming, suggesting that either different batches of manure were used or there are other problems: differences in quality of measurements between labs or on different days. The authors should have compared control and the two biochars at two rates simultaneously, with five measurements on the same day. This would reduce this source of error. I encourage the authors to please review their data, address the comments, and then re-submit this manuscript for publication. At present, it is not ready for publication.

Reviewer 2 Report

This manuscript described the real-time concentration measurement of NH3 and H2S during swine manure agitation before pump-out. It may be beneficial to the practical applications of biochars. However, some of the data was not well-presented and some exceeded the quantification range, making them less valuable and trustworthy. So I would reconsider it after a major revision. Some specific comments were listed as follows.

1. The authors compared many different parameters to evaluate the biochar performance on reducing the concentration of NH3 and H2S. Such as max flux, overall total emission, total emission during 3-min agitation and so on. Which one do the authors believe could be the most representative to evaluate the performance of Biochars?
2.  Two citations from the authors groups (citation 17 and 18) was not physically accepted. One is under review and the other is not submitted yet. I do not believe they could be the citations. And even if these two citations were accepted, I would prefer the authors declare the differences between these two citations and this manuscript.
3. Line 99, what does it mean for “7.5 air exchanges per h”? Does it mean 7.5 times? Or 7.5 m3 ?
4. Line 103, what does “d.m.” mean?
5. Line 102-104, What is the specific procedures to make RO and HAP biochars? What is the pyrolysis temperature?
6. All the concentration unit. For example, in table 1, is the unit for “Pre-agitation H₂S” “mg/m2/s”? or should it be “mg/m3/s”?
7. Table 2. Why thinner biochar layers show worse reduction? What is the limit of quantification for NH3 and H2S? What is the highest and lowest concentration that the detector can measure? The authors declared that some of the data point exceed the highest quantification limit? Then how trustworthy is the data and the comparison?
8. Table 3. should be 0.0367, or 0.367?
9. What is the mechanism for biochar to reduce the emission of NH3 and H2S? is it because of biochar adsorption, or because of the inhibition of biochars on the microbe activities in manure?
10. Line 223, Proof for the more porous structure in HAP biochars?
11. Appendix A. Change the shape or color of "average 0.25"". It is hard to tell if all of they are in circular black.