The Impact of Surficial Biochar Treatment on Acute H₂S Emissions during Swine Manure Agitation before Pump-Out: Proof-of-the-Concept

Round 1

Reviewer 1 Report

The manuscript concerns a fairly important issue which is an attempt to mitigate hydrogen sulfide emissions during swine manure agitation. The authors attempted to evaluate 6 mm and 12 mm biochar treatments for mitigating H₂S emissions during swine manure agitation. Two biochars were used - one made from corn stover and the other from read oak. The manuscript addressed some interesting issue but there are few minor points which need to be clarified or improved:

1. Insufficient information why the authors choose 6 mm and 12 mm thick layers of biochar applied to the manure. Please clarify this choice.
2. No mention of replicates in the study. Were the experiments replicated?
3. It is not known whether biochars were used as soil amendments or adsorbents. – If biochars were also used as adsorbents, their physicochemical characteristics should be supplemented by the determination of specific surface area using for example the BET method or the Iodine Adsorption Number.
4. If biochars were also used as adsorbents, it would be a good idea to perform (for comparison) experiments using commercially available charcoal. Have the authors conducted such tests?
5. There is no in-depth discussion of the results in this manuscript. Please improve the discussion.
6. Line 277-278: You say “Application of powdery, light material might not be feasible in farm conditions. Pelletized biochar could be a more practical and safer mode of application.” I am not sure if it is a good idea to use pelletized biochar because of its weight (the bigger chunks can sink and mix with manure).

Overall, the manuscript contains quite interesting research that can help reduce farmers' exposure to inhalation of H₂S. I am able to recommend the manuscript for publication after minor revision.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript, the authors investigated the effect of biochar on emission of H2S from manure storage pit and found that 6 mm biochar treatments rather than 12 mm is effective to reduce the maxim peak of H2S generation.

Introduction is written properly, which leads to readers to understand the current problem on this field. Results section is also written well but reliability of some data is in doubt. The finings of this manuscript is interesting but revision for the following points is required to accept this paper for the publication.

1. line 166. "The 12 mm biochar treatment reduced the concentration of H2S by 68.3%"

-> The value of 68.3% might be wrong, The amount of H2S of 12 mm biochar is larger than that of 6 mm biochar, indicating that reduction % of 12 mm should be smaller than that of 6 mm.

2. Line 200, Table 4: The value of 0.455 for Control would be 0.0455. If this value is correct, % Reduction of maximum peak flux (42.5 and 60.6) is wrong.

3. Figure A1 shows relatively smaller error bars for 6 mm RO, but large error bars for control (after 7min) and 12 mm RO. Although it is visually apparent, the error value of 6 mm biochar in Table 3 is larger than that of control (0.472/ 2.34 > 0.644/7.18) and comparable to that of 12 mm. The deviations listed in Table 3 do not seem to correspond to Figure A1.

4.Line 127: As written in Experiments section, each experiments was triplicated. However, the difference between each run is so large. For example, Figure A4 is quite different from Figure A5. The reviewer understands the difference of the control values between RO and HAP experiments due to different manure used for experiments. However, the same manure was used for the same experiment (Figure A3-A5, A6-A8 etc), but the results were greatly different. Is there any reason of such large deviation in each run?

5. Discussion: There is no discussion about the kinetic results. It is needed.

Author Response

Please see the attachment.

Author Response File: Author Response.docx