Physical Properties of Dairy Manure Pre- and Post-Anaerobic Digestion
Round 1
Reviewer 1 Report
Authors proposed the simple method for density and TS prediction for pre-digested manure., which might be very useful when calculating CH4 productivity. The structure is correct, the aim is clearly stated. Methods are well described, results are clearly presented. I would suggest more references in the discussion section, now it contains only a few references. Conclusions are drawn on the basis of the results.
Some spellings p.5, 151-152: it is kg m-3, it should read: kg m-3
Author Response
Comments and Suggestions for Authors
Authors proposed the simple method for density and TS prediction for pre-digested manure., which might be very useful when calculating CH4 productivity. The structure is correct, the aim is clearly stated. Methods are well described, results are clearly presented. I would suggest more references in the discussion section, now it contains only a few references. Conclusions are drawn on the basis of the results.
Some spellings p.5, 151-152: it is kg m-3, it should read: kg m-3
Response
Thank you for your review and comments. We have complemented the discussion section with relevant references where appropriate as suggested. We have also reviewed the paper for English usage and corrected the typos.
Reviewer 2 Report
- table 2: insert farm description parameters in this table
- use only data from the 5 similar farms
- ttile should be change adding the mention about "solid manure bedding"
- mention about CH4 production should be removed
Author Response
Response to review report
Thank you for taking the time to review our manuscript. The manuscript has improved based on your suggestions. The usage of the English language has been reviewed. The introduction has been complemented with references and background information to better present the contribution of the paper. We have better explained that the samples used to build the overall density and total solids model were all from the five similar farms using separated manure as bedding (no statistical difference). Finally, we have reviewed the conclusions so they can better reflect the results.
Comments and Suggestions for Authors
Comment: table 2: insert farm description parameters in this table
Response: The farm management practices relevant to the study were added in Table 2 as suggested. These include: substrate, bedding type, and digester type.
Comment: use only data from the 5 similar farms
Response: We understand the source of confusion. The overall model analyzing density as a function of total solids from 1.5% to 50% only considers the five farms using solid manure as bedding. This was not explicitly mentioned in the original submission of the manuscript. We have explicitly mentioned this in Figures 2 and 3 and added the following sentence: “Figures 2 and 3 fit a model as a function of TS ranging from 1.5% to 50%. This model includes the additional samples for pre-digested dairy manure (farms H, I, and J) and the samples of the five farms that use manure solids as bedding, excluding farm B (using sand as bedding) and farm F (co-digesting manure with food waste)”. In addition, Figure 1 presents the linear models for the five farms with manure solids, the farm with sand bedding, and the sand co-digesting manure with food waste separately. The statistical analysis shows that the characteristics of manure are different in these two farms. We have acknowledged this difference in the results section. We believe that it is important to present the results of these two farms, as they represent common management practices in real life dairy systems and provide valuable information not only for these farms, but also for researchers in the field.
Comment: title should be change adding the mention about "solid manure bedding"
Response: We have changed the title as suggested to: “Physical Properties of Manure Pre and Post Digestion in Dairy Farms using Separated Solids as Bedding”
Comment: mention about CH4 production should be removed
Response: We understand that this sentence was disconnected from the text and seemed out of context. We meant to highlight the importance of this methodology to further predict biogas or methane production by other studies or models. We have changed the sentence to reflect this to: “The VS destroyed can be obtained by the difference between VS of pre-digested manure and post-digested manure. This methodology can be used to estimate biogas or methane production from AD systems with similar characteristics than the ones analyzed in this study”.
Round 2
Reviewer 2 Report
If I understand well, Farm B don't use solid manure bedding. So, I think that farm should be not considiered in the study.
Author Response
Comments and Suggestions for Authors
If I understand well, Farm B don't use solid manure bedding. So, I think that farm should be not considiered in the study.
Response: That is correct. Farm B uses sand as bedding. We agree that sand has different properties than manure separated solids. As a result, we have not included Farm B as part of the overall TS vs Density model (Figures 2 and Figures 3). We have clarified this in the abstract and in the text of the manuscript. The results of Farm B are presented separately. We believe that the results of Farm B using sand bedding are useful for comparison purposes and are a representation of a large population of dairy farms using sand as bedding. Different farms have different practices. For example, one farm use sand bedding, while the others use manure separated solids. Also, two farms use complete mix digesters, while the others use plug-flow digesters. The manuscript presents the detailed information regarding all farm’s management practices, so the reader is aware of these differences. We have also adjusted the title of the manuscript to: “Physical Properties of Dairy Manure Pre and Post Anaerobic Digestion” to better encompass all farms presented in the analysis.
