Fractionation of Lignocellulosic Fibrous Straw Digestate by Combined Hydrothermal and Enzymatic Treatment

Round 1

Reviewer 1 Report

The manuscript ID energies-1820249 entitled "Fractionation of lignocellulosic fibrous straw digestate by combined hydrothermal and enzymatic treatment" covers interesting and very current research topics. Optimizing the management and use of lignocellulosic biomass and digestate is an important aspect of the functioning of agricultural and utilization biogas plants. The manuscript may be published, however, it needs to be supplemented. My critical remarks below:

-       Authors should consider preparing a graphical abstract as it will be useful for readers to understand the inspiration and flowchart of the experiments.

-       In the Introduction, there is no information regarding the previous research. It needs to be completed. The authors should define the meaning of the hydrothermal pre-treatment of digestate sludge. Isn't it better to use this type of solution for the preparation of raw substrates, before the anaerobic digestion process? Please refer to the existing literature data.

-       The Introduction section should be supplemented with an indication of the use of thermal pre-treatment for very important topic which is microalgae biomass: https://doi.org/10.1016/j.biortech.2013.09.121, https://doi.org/10.3390/molecules23092096 and the different methods of hydrothermal depolymerization of lignocellulosic biomass: https://doi.org/10.1016/j.biombioe.2019.105324, https://doi.org/10.3390/pr7010024,

-       It is necessary to formulate the research hypotheses that have been verified. The authors should state what they expected when planning the experimental work. What inspired me to undertake the research in question. What do they bring to the commonly known knowledge and how do they differ from already conducted experiments. Authors should determine whether the verification of the hypotheses was positive and whether they achieved the expected, expected results.

-       Design of research works should be included at the beginning of the Material and methods chapter. The Authors should clearly and clearly present the division of experiments into stages, series and research variants. Perhaps the scheme of the experiments carried out would be useful. Please provide a flowchart for scheme of research design to be more sensible for readers.

-       How did the authors plan the experiments? What statistical or optimization tools for investigation planning did they use? Please provide the manufacturer and model of the ferrite magnets used in the experiment.

-       The biggest weakness of the manuscript is the lack of statistical analysis of the presented results. Failure to apply appropriate methods and statistical tests eliminates the manuscript from a scientific point of view. It is necessary to define what statistical methods were used to assess the significance of differences between variables.

-       In how many repetitions the experiments were performed?

-       Author should also pay more attention to the practical implications of this study, outlining the challenges in the current research, future work, and recommendations. It is recommended to discuss and explain the appropriate policies based on the findings of this study. In addition, the results should be further elaborated to show how they could be used for real applications. Is it feasible on a large scale? Is it technically feasible outside the laboratory? Is it even possible? Does it make sense? Will it be profitable? There are many problems to discuss.

-       The analysis of results should be extended by determining the correlation between the analyzed variables.

-       In my opinion, based on the results presented in the manuscript, it is difficult to determine the effectiveness of the technological solution used. Information on the characteristics of the substrate is not enough to determine its usefulness in methane fermentation processes. The authors should consider performing simple respirometric tests that will verify the amount of biogas and methane produced. Without this kind of information, the reader does not know whether the treatment of thermal depolymerization and enzymatic hydrolysis makes practical and economic sense.

-       If it is currently impossible to perform this type of test, please discuss this issue in depth.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

I read with interest about this manuscript reporting on lignocellulosic fibrous straw. Overall, I believe the paper could be of potential interests to the Journal. I however recommend that the reviewers fully address these issues/comments raises as follows.

 

1. The introduction, while informative, appears to be quite lengthy. The authors could consider sharpen it a bit by bringing out the key points more clearly.

 

2. In fig. 3, why a max treatment time of 120 min is chosen? What about longer treatments? Clearly the trend doesn't plateau as it does in Fig. 4

 

3. The brightness/contrast of FIG. 6 doesn't seem to be optimal.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In my opinion manuscript has been deeply improved and it can be publish in current form.

Author Response

We would like to thank the reviewer again for his efforts and support in improving the paper.