Coupled Biogas and Fiber Production from Agricultural Residues and Energy Crops with Steam Explosion Treatment

Round 1

Reviewer 1 Report

General comment

Agricultural biogas production is an integral part of the circular bioeconomy. In this context, authors present a bioeconomic concept based on the anaerobic digestion process to provide methane as a versatile energy carrier and fibers for material use in a coupled process. Therefore, this study was designed to (i) investigate the suitability of a broad range of agri-based fibrous feedstocks and (ii) to test the feasability of a combined processing via steam explosion treatment followed by solid-liquid separation. Thus, the study presented is on a topic of relevance and general interest to the readers of the journal.

The article is generally well-structured but with linguistically weaknesses (unprecise wording, partly colloquial language “written as spoken” particularly the Result & Discussion and Conclusions Section). Please, revise entire manuscript.

Terminology “Substrate” / “Feedstock” is used inconsistently. Please revise (entire manuscript) as follows: “Feedstock” when regarding the supply chain, befor feeding the biomass in the fermenter. “Substrate” is the biomass in the fermenter.

Name of biomass variants investigated: to be precise and consistent add “silage” to “Sylvatic silphia” such as for “nettle silage” (entire manuscript, tables and figures).

For example: L122 + 140: “… was done …”; colloquial language, please rephrase; entire manuscript.

 

 In general, there are a few items that need to be addressed in this manuscript prior to publication.

1.) Author List  

L4: Elviliana? Please, provide authors full name

 

2.) Abstract: Needs revision: (i) considering revison of the chapter 1 Introduction (see comment below) and (ii) rephrasing, for example:

L22f: “ … substrate itself… , and a number of …, … around … “ Do you mean (i) characteristics, (ii) which one ? (iii) approx. rather than around. Please, state clearly and avoid colloquial language (entire manuscript).

 

3.) Key words: Use keywords pointing to issues not already mentioned in the title of the paper. For example add silage, liquid and solid fractions

 

4.) Introduction: I would wish to find the focus of the study to be presented more coherent and precise in the introduction. Authors should start with more general introducing sentences to biogas in the context of bioeconomy and not with an excursion to the EEG which do not provide a purposeful introduction to the topic. Particularly as the EEG is a very special, German, aspect.

L 70: “This …” What do you mean? What has a huge impact? Please, rephrase.

L78: “Sylvatic silphia silage” rather than “Sylvatic silphia”; see general comment above.

L78 + 80: typo: Miscanthus rather than Mischantus; check entire manuscript

 

5.) Materials and Methods

L83ff: Chapter 2.1 Substrates and sampling: Are the listed places practice farms? Could you please provide information on the scale and how the biomasse were (temporarily) stored. In plastic bins (volume)? At ambient temperature?

L112: “MPA”: Do you mean unit MPa?

L114f: “As the optimum water content in this process is crucial for the efficiency of the process and the total operational cost …”  -> Please, delete this statement which should be provided in the introduction and not in the M&M chapter.

Table 1: typo: sylvatic rather than  slyvatic; add “silage”; see general comment.

L122 + 140: “… was done …”; colloquial language, please rephrase

 

L179f: “…for most of the substrates …”;  please add “investigated”; revise entire manuscript

 

L195: wording: “require” rather than “lead”

L200: “The ODM content …”; add “(Table2)”

L200: “indicate” rather than “showed” 

L203: “This may cause problems …”; in which way? State clearly: … such as …

 

Figure 2+3: y-axes; iniform axis labeling (ODM); revise

L263: typo: Weender ….Soest

L264f: raw protein and raw fat are not shown in any table? If so, add “(not shown)”

L264f: PH-Values presented in Table 4 are not considered in the discussion; please add in the text

L276/L305/entire manuscript: “…potential is not used”; revise wording: “potential is not fully exploited”

L276/325: “won’t be”; didn’t; colloquial language, please rephrase

 

L314: Do not start a section with “Table x shows”; revise

L329: Figure 5 rather than 4

L336: typo: particle

Author Response

Dear Reviewer,

Thank you for your comments. We have adapted the script accordingly.

 

Best regards,

Benedikt Hülsemann

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript describes coupled biogas and fiber production from agricultural residues and energy crops with steam explosion treatment. The manuscript is interesting in process viewpoint. The manuscript needs amendments prior to publication.

Abstract
1. Rewrite abstract. Abstract not clear. Provide 'real values' for main findings. Good abstract - short introduction, objectives, method, main findings, short discussion, short conclusion.

Introduction
1. Line 31 - On this basis for 2018, biogas...Provide current data.
2. Line 52 - Why you choose SE method rather than available method in the literature? Justify. Compare and contrast with other literature. List advantages/disadvantages.
3. Discuss problem statement and relate with international/national policy. i.e. SDG2030
4. Objectives were not clear. Be specific. include manipulated and responding variables.

Methods
1. Why you chose so many materials in your study? Justify.
2. Line 84 -99 - Why you need to separate paragraph?
3. Provide overall flowchart of methodology used includes preparation, optimization (if any)/experimental design, analysis, characterization, etc in this study. So that reader could understand better about the work.
4. section 2.2 - steam explosion, provide schematic diagram with label/dimension.
5. Are you developing your own method? cite any necessary method used from literature.
6. How do you set parameters (temperature, s/s ratio, reaction time, pressure, etc) used for SE? Any preliminary study? references? provide citation.
7. Reference for equation 1?
8. Any statistical method used? Why? If not, please add.
9. Section 2.6 too general. Please rename section 2.6

Results and Discussion
1. Section 3.1 Mass balance - major concern on the data. ambiguous? mass balance should be 100%. Why the results show less or more than 100%? Re-look on the data.
2. Why you need figure 2? repetition of data from figure 1? difference presentation? justify.
3. It is meaningless if you show tables/figures without explaining with citation/compare with other studies - figure 3. please add.
4. line 241-242 - two times on the other hand..
5. line 241 - suggests an economic use of the liquid phase in a biogas plant
6. Figure 1 was not mentioned in the text.
7. Table 2 was not mentioned in the text.
8. Table 3 - i have concern here. why the std deviation 0? too perfect? any justification
9. Line 249 - Explain how the moisture content ratio increases the efficiency of SE pretreatment?
10. Line 275 - limit the possible applications such as?
11. Line 307 - However, it is necessary to compare the additional cost with the benefits of an additional operation step and considering the fiber quantity and quality. Can you provide economic cost analysis here? discuss critically by adding one section about cost analysis.
12. Line 325 - Average particle size and water adsorption capacity didn't show any dependence. Why? Supports with scientific explanation.
13. Provide std deviation for table 5/any  figures or tables.
14. Figure 5 - the results show not much difference between untreated and treated. justify.
15. Figure 5 - why caption differ from legend? which one treated vs untreated or none pretreatment vs SE? definition of terms need to be introduced earlier.

Conclusion
1. rewrite conclusion, should reflect objectives, provide 'real values'. include suggestion/recommendation.

References
1. Check consistency of format used. 

Author Response

Dear Reviewer,

Thank you for your comments. We have adapted the script accordingly.

 

Best regards,

Benedikt Hülsemann

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors addressed the suggestions of reviewers and significantly improved the quality of the manuscript. But not all (of my) hints were consistently implemented. Unfortunately, new errors have appeared as a result of the editing. The manuscript is not yet ready for publication. There are a few items that need to be addressed in this manuscript prior to publication:

Abstract:  L17: capitalization – to be consistent:  Flax

Figure 1: a) Typo in scheme text: separation rather than seperation; b) unit – as mentioned in review round 1: MPa rather than MPA; c) Caption: formatting – to be consistent: Overall rather than overall

L128:  typo: Alfalfa rather than Al-falfa

L129-129: incorrect punctuation twice - before parenthesis placement

L154: capitalization – to be consistent: Solid-liquid separation

L185: delete the word “acid”; It should read: … of the volatile fatty acids, acetic acid, propionic …

L207: The reference to “Table 2” was mistakenly deleted: please reinsert.

Table 2: inconsistent formatting in the table header: check capitalization

L326 + L349: incorrect punctuation - before parenthesis placement

Table 5: inconsistent formatting in the table header: check capitalization

L363ff: as mentioned in review round 1: be precise and consistent and add “silage” to “sylvatic silphia” such as for “nettle silage”

 

Author Response

Dear Reviewer,

Thank you for your answer and afford.

 

Abstract: L17: capitalization – to be consistent: Flax

Thanks for the advise. We change it.

Figure 1: a) Typo in scheme text: separation rather than seperation; b) unit – as mentioned in review round 1: MPa rather than MPA; c) Caption: formatting – to be consistent: Overall rather than overall

Thanks for the advise. We changed all of your points.

L128: typo: Alfalfa rather than Al-falfa

We correct that point.

L129-129: incorrect punctuation twice - before parenthesis placement

We correct that point.

L154: capitalization – to be consistent: Solid-liquid separation

Thanks for the advise. We changed every word to a capital letter.

L185: delete the word “acid”; It should read: … of the volatile fatty acids, acetic acid, propionic …

Thanks for the advise. We revised this sentence.

L207: The reference to “Table 2” was mistakenly deleted: please reinsert.

Thanks for the advise. We add it.

Table 2: inconsistent formatting in the table header: check capitalization

We correct it.

L326 + L349: incorrect punctuation - before parenthesis placement

We correct it.

Table 5: inconsistent formatting in the table header: check capitalization

We used a capital letter "Water..."

L363ff: as mentioned in review round 1: be precise and consistent and add “silage” to “sylvatic silphia” such as for “nettle silage”

We checked this point again. Thank you for your advise!

Reviewer 2 Report

Suggestion Fig. 1 should be placed in section 2. Materials and method. not in introduction.
Other corrections - acceptable.

Author Response

Thank you for your answer and afford.

We changed the position of Fig. 1 to the section 2. It is renamed as Fig. 2 now.