Enhancing Biogas Production of Co-Digested Cattle Manure with Grass Silage from a Local Farm in Landshut, Bavaria, through Chemical and Mechanical Pre-Treatment and Its Impact on Biogas Reactor Hydraulic Retention Time
Xihui Kang
Round 1
Reviewer 1 Report
The manuscript entitled "Enhancing biogas production of co-digested cattle manure with grass silage from a local farm in Landshut, Bavaria, through chemical and mechanical pretreatment" comprehensively evaluated the co-digestion performance of cattle manure and grass silage. The manuscript must be improved before publishing and should be revised regarding the following parts:
1. Abstract: this part did not well present the findings of the study. It should contain the changes before and after pretreatment or the optimal results found in the study, not the narrative description of the manuscript without statistical results.
2. Introduction: the research gap in the current research field is not well stated and the contribution of the manuscript is not well explained either. Do not list the structure of the lignocellulose as this is not a review paper, the authors should focus on the novelty of the current study and what they are trying to present.
3. Figure caption: the caption of each figure should be added. For example, for figure 2, the caption is missing and it is hard for readers understanding the meaning of experiments 1, 2 ...
4. The authors should focus on the results and try to put the experimental setup table into the supplementary files as this is the core part of the study. In Table 1, it is easy to get confused if it is the parameters of cattle manure alone or the mixed substrate.
5. Although the authors presented a lot of data in sCOD, it is better if the authors can present the changes in glucan, xylan, and lignin contents before and after NaOH and KOH pretreatment. It is known that the structural recalcitrance of lignocellulose makes it hard to digest and alkaline pretreatment is efficient in dissolving lignin and hemicellulose.
6. The reference should be added where applicable. In some parts, the author stated according to the literature, but the reviewer did not see any literature cited.
7. The conclusion part is missing and also the discussion in the Result section is not that strong. There are a lot of studies evaluating the co-digestion of animal manure and lignocellulose with the application of pretreatment. It should be easy for the authors to find relevant citations.
8. The English of the manuscript should be improved. The reviewer got confused when reading some parts of the study which is not annoying.
Author Response
Dear Referee,
thank you very much for your comments and observations. Please receive our answers:
- Abstract: this part did not well present the findings of the study. It should contain the changes before and after pre-treatment or the optimal results found in the study, not the narrative description of the manuscript without statistical results.
Answer: the abstract has been modified according to the observations. Results from the pre-treatment studies with the sCOD increment after applying chemical and shredding pre-treatment as well as the achieved pH values have been added. The pre-treatment effect on the biogas fermentation – an 18 days shorter period of fermentation – has also been presented.
- Introduction: the research gap in the current research field is not well stated and the contribution of the manuscript is not well explained either. Do not list the structure of the lignocellulose as this is not a review paper, the authors should focus on the novelty of the current study and what they are trying to present
Answer: the introduction has been revised. In our opinion, the structure of the lignocellulose is important to understand how the pre-treatments work so there is still information about this issue included in the introduction. Relevant facts about the investigation gap have been included, especially about how to apply the pre-treatments in an optimal concentration and duration to facilitate its application to larger scale projects. More literature about co-digestion has also been included.
- Figure caption: the caption of each figure should be added. For example, for figure 2, the caption is missing and it is hard for readers understanding the meaning of experiments 1, 2 ...
Answer: figure capitation has been revised Tables 2, 3 and 4 are explained in detail now.
- The authors should focus on the results and try to put the experimental setup table into the supplementary files as this is the core part of the study. In Table 1, it is easy to get confused if it is the parameters of cattle manure alone or the mixed substrate.
Answer: the comments will be taken into account. Tables will be uploaded as supplementary files. Table 2 is better explained now.
- Although the authors presented a lot of data in sCOD, it is better if the authors can present the changes in glucan, xylan, and lignin contents before and after NaOH and KOH pretreatment. It is known that the structural recalcitrance of lignocellulose makes it hard to digest and alkaline pretreatment is efficient in dissolving lignin and hemicellulose
Answer: the research was mainly focused on the total energy content from the lignocelluloses and how it got more solubilized in comparison to the untreated lignocelluloses, so that the sCOD was considered the most important parameter.
The changes in glucan, xylan and lignin contents have not been analyzed during this investigation.
- The reference should be added where applicable. In some parts, the author stated according to the literature, but the reviewer did not see any literature cited.
Answer: the references has been added.
- The conclusion part is missing and also the discussion in the Result section is not that strong. There are a lot of studies evaluating the co-digestion of animal manure and lignocellulose with the application of pre-treatment. It should be easy for the authors to find relevant citations.
Answer: conclusion has been added and the text has been completed with more related literature.
- The English of the manuscript should be improved. The reviewer got confused when reading some parts of the study which is not annoying.
Answer: that remark has been taken into account.
Reviewer 2 Report
The authors have presented relevant research work for the current scenario.
The authors may address the following:
1. Abstract should be rewritten. It should present crisp information on your research and finding.
2. Research gap should be presented properly.
3. Authors should focus more on recent literature than old literature.
4. Conclusion section should be added.
Author Response
Dear Referee,
Thank you very much for your comments and observations. Please receive our answers:
- Abstract should be rewritten. It should present crisp information on your research and finding
Answer: the abstract has been modified according to the observations. Results from the pret-reatment studies with the sCOD increment after applying chemical and shredding pre-treatment as well as the achieved pH values have been added. The pre-treatments effect on the biogas fermentation – an 18 days shorter fermentation period – has also been presented.
- Research gap should be presented properly.
Answer: the introduction has been revised. Relevant facts about the research gap has been included, especially about how to apply the pre-treatments in an optimal concentration and duration to facilitate its application to larger scale projects. More literature about co-digestion has also been included.
- Authors should focus more on recent literature than old literature.
Answer: more recent literature has been added.
- Conclusion section should be added.
Answer: conclusion has been added and the text has been completed with more related literature.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
The abstract still needs to be revised and condensed.
Author Response
Landshut, 15th. January 2023
Dear Referee,
Thank you for your observations and comments. The abstract has been reduced according to your comments.
Regarding to the English, please note that a professional proofreading service in England revised the manuscript two weeks ago.
Best Regards
- Sc. Verónica Hidalgo Sánchez
Wissenschaftliche Mitarbeiterin
HOCHSCHULE LANDSHUT
University of Applied Sciences
Am Lurzenhof 1, 84036 Landshut
Raum: D1 09
Tel. +49 (0)871 - 506 472, Fax + 49 (0)871 - 506 9472
www.haw-landshut.de
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors have addressed the review comments satisfactorily. The paper can be accepted.
Author Response
Landshut, 15th. January 2023
Dear Referee,
Thank you very much for your positive feedback and observations.
Best Regards
- Sc. Verónica Hidalgo Sánchez
Wissenschaftliche Mitarbeiterin
HOCHSCHULE LANDSHUT
University of Applied Sciences
Am Lurzenhof 1, 84036 Landshut
Raum: D1 09
Tel. +49 (0)871 - 506 472, Fax + 49 (0)871 - 506 9472
www.haw-landshut.de
Author Response File: Author Response.pdf
