Round 1

Reviewer 1 Report

The manuscript presents a contribution on the production of the hydrochar from brewer’s spent grains at different conditions and its characterisation. The text is well written although a further improvement of the organisation of results should be performed. A review of the English should be performed. I would suggest to perform the following modifications in order to improve the quality of the work:

-          Abstract: I would suggest avoiding abbreviations. Also, I would reformulate the sentence 15-16: the obtainment of hydrochar was performed at different operational conditions and successively its characterization was performed

-          The objective of the work should be reformulated in a more direct and clear way

-          How were the values in Table 1 obtained? Are they from literature instead? If so, please add the reference. Why was the protein content calculated by multiplying the N content by 6.25?

-          The variation of time in the two step process is not clear: it is stated that 2 and 4 hours were tested (line 114) but then the process is described as 1 hour of heating and 3 of reaction (line 130). Please clarify

-          Please add references for Eq. 1

-          Description of Table 2: Proximate analysis and fuel ratio

-          Line 199-200 should be referenced

-          Please refer the basis of the solid, liquid and C compositions (mass?)

-          In general, I would suggest to divide the discussion of results into two sections in order to clarify the concepts: that explaining the results from a traditional 1 step process and another one with the discussion of the two-step process.

-          Please add the basis of the elemental analysis (mass?)

-          Line 317: how do you know that 5-hydroxymethylfurfural is present in the sample?

-          Please add all the ASTM normative used in this work in the reference list

Author Response

Dear Dr,

We are very grateful for your e-mail and for the comments of the reviewers, which we consider contribute to the improvement of the work.

            We have revised the work taking into consideration the suggestions of the reviewers. Furthermore, following your hints on how to make the changes, we have highlighted in yellow those parts of the text from the manuscript that have been modified.

An itemized list of the changes made in the revised manuscript and our response to all the issues raised by the reviewers is attached below.

Reviewer #1

-          Abstract: I would suggest avoiding abbreviations. Also, I would reformulate the sentence 15-16: the obtainment of hydrochar was performed at different operational conditions and successively its characterization was performed

Concerning the abbreviations, we made the change suggested by the reviewer.

-          The objective of the work should be reformulated in a more direct and clear way

We have made the change suggested by the reviewer.

-          How were the values in Table 1 obtained? Are they from literature instead? If so, please add the reference. Why was the protein content calculated by multiplying the N content by 6.25?

            Values from Table 1 were obtained by the methodology explained in the method section. The protein was multiply by the value of 6.25 because we followed the ASTM D-5291 (see footer of the Table 1).

-          The variation of time in the two step process is not clear: it is stated that 2 and 4 hours were tested (line 114) but then the process is described as 1 hour of heating and 3 of reaction (line 130). Please clarify

We have made the change suggested by the reviewer.

-          Please add references for Eq. 1

            Reference was indicated on the previous paragraph, but it also is added a sentence to clarify it.

-          Description of Table 2: Proximate analysis and fuel ratio

We have made the change suggested by the reviewer.

-          Line 199-200 should be referenced

We have made the change suggested by the reviewer.

-          Please refer the basis of the solid, liquid and C compositions (mass?)

We have made the change suggested by the reviewer.

-          In general, I would suggest to divide the discussion of results into two sections in order to clarify the concepts: that explaining the results from a traditional 1 step process and another one with the discussion of the two-step process.

It is not possible make the change suggested by the reviewer because the two-steps process have to be compared with the one-step process results.

-          Please add the basis of the elemental analysis (mass?)

We have made the change suggested by the reviewer.

-          Line 317: how do you know that 5-hydroxymethylfurfural is present in the sample?

It was known that it some HMF present in our sample because Table 5. shows the yield to HMF after hydrothermal carbonization.

-          Please add all the ASTM normative used in this work in the reference list

We have made the change suggested by the reviewer.

We believe that the concerns of the reviewers have been adequately answered, and hope that the work may be published in Energies Journal.

                        Sincerely yours,

                        PhD candidate Pablo J. Arauzo

Reviewer 2 Report

HYDROTHERMAL CARBONIZATION BREWER’S SPENT GRAINS WITH THE FOCUS ON IMPROVING THE DEGRADATION OF THE FEEDSTOCK

The manuscript deals with an interesting subject, the conversion of biomass into liquid form. Unfortunately the manuscript must be significantly rewritten in order to be accepted. The authors must be much more exact in the use of terms and units. A laguage check by a native english speaker is stronly adviced.      

Below some examples on changes needed can be found, this list in not complete because the need for extensive rewriting    

1) In the Guide to Authors  is written: "Abstract: The abstract should be a total of  about 200 words maximum. The abstract should be a single paragraph and should follow the style of structured abstracts, but without heading". According to this the Abstract shoud be one single paragraph not two.

2) Some numerical results could be presented in the Abstract, the reults on lines 18-19 is most likely better presented by numbers instead of some words

3) In the Reference list, 2 different ways to write the journals are used. The authors are suggested to use eighter  full names of the journals or the short names but not a mix of both ways. Check for the proper way in the Instructions for Authors.

4) Reference 10. Why are the names written i CAPITAL letters? The same principle must apply for all references.

5) on line 74 the process is called a two-steps process while it on line 82 is a two-step process: The authors are suggested to be more exact when describing the process, if the same processes are described?

6) The temperature rise described on lines 114-115 is normally called a temperature ramp and should be given as C/minute.

7) Line 151 "particle size smaller than 150-200 m". Normally this is not given as an intervall, particles are smaller than 150 or smaller than 200. The unit m used cannot be the coorect unit. The text on line 151 must be reformulated.

8) on lines 154 and 156: Use the upper index  for min-1 not min-1.

9) on line 159 the authors state "TOC of liquid sample was calculated using TOC Analyzer 5050A". I think that the TOC was measured using the analyzer and calculated using a certain procedure not described in the text. The authors must be much more exact in the way they describe the procedures.

10) This text (lines 157-161) is to some extent a unclear and must be rewritten

157 2.3.2 Liquid fraction
158 • Total organic carbon (TOC)
159 TOC of liquid sample was calculated using TOC Analyzer 5050A (Shimadzu Scientific 159 Instruments, Columbia, MD, USA).
161 • High performance liquid chromatography (HPLC)

11) Are tables 1, 2, and 3 results or just part of the methods? Up to me thay should be presented as results and be moved to the right places. Table 2 under section 3.2 ...

12) Why is theis comparision between biomass as general and sugars made in the abstract ection? "Unfortunately, severe conditions for complete conversion of carbohydrate inside the biomass structure are necessary, especially compared to the conversion of sugar compounds."

13) line 369, Temperature, time etc are not conditions, they are parameters

Author Response

Dear Dr,

We are very grateful for your e-mail and for the comments of the reviewers, which we consider contribute to the improvement of the work.

            We have revised the work taking into consideration the suggestions of the reviewers. Furthermore, following your hints on how to make the changes, we have highlighted in yellow those parts of the text from the manuscript that have been modified.

An itemized list of the changes made in the revised manuscript and our response to all the issues raised by the reviewers is attached below.

Reviewer #2

1) In the Guide to Authors  is written: "Abstract: The abstract should be a total of  about 200 words maximum. The abstract should be a single paragraph and should follow the style of structured abstracts, but without heading". According to this the Abstract shoud be one single paragraph not two.

We have made the change suggested by the reviewer. Both paragraphs are as single one.

2) Some numerical results could be presented in the Abstract, the reults on lines 18-19 is most likely better presented by numbers instead of some words

            According to the understanding of the review’s suggestion, it was made changes on the abstract section.

3) In the Reference list, 2 different ways to write the journals are used. The authors are suggested to use eighter full names of the journals or the short names but not a mix of both ways. Check for the proper way in the Instructions for Authors.

We have made the change suggested by the reviewer.

4) Reference 10. Why are the names written i CAPITAL letters? The same principle must apply for all references.

Reference 10 was in capital letter due to the program used for citation. We have made the change suggested by the reviewer.

5) on line 74 the process is called a two-steps process while it on line 82 is a two-step process: The authors are suggested to be more exact when describing the process, if the same processes are described?

            It is always two-steps process, so it was modified along the submitted paper.

6) The temperature rise described on lines 114-115 is normally called a temperature ramp and should be given as C/minute.

            The suggestion is not possible because the heating of the reactor is not linear.

7) Line 151 "particle size smaller than 150-200 m". Normally this is not given as an intervall, particles are smaller than 150 or smaller than 200. The unit m used cannot be the coorect unit. The text on line 151 must be reformulated.

It has been replaced.

8) on lines 154 and 156: Use the upper index for min-1 not min-1.

It has been replaced.

9) on line 159 the authors state "TOC of liquid sample was calculated using TOC Analyzer 5050A". I think that the TOC was measured using the analyzer and calculated using a certain procedure not described in the text. The authors must be much more exact in the way they describe the procedures.

We have made the change suggested by the reviewer.

10) This text (lines 157-161) is to some extent a unclear and must be rewritten

157 2.3.2 Liquid fraction

158 • Total organic carbon (TOC)

159 TOC of liquid sample was calculated using TOC Analyzer 5050A (Shimadzu Scientific 159 Instruments, Columbia, MD, USA).

161 • High performance liquid chromatography (HPLC)

Sentence and equation were added to make it clear.

11) Are tables 1, 2, and 3 results or just part of the methods? Up to me thay should be presented as results and be moved to the right places. Table 2 under section 3.2 ...

We have made the change suggested by the reviewer, please notice that the change of the table into the section 3.2 produced a change into the name to Table 3.

12) Why is theis comparision between biomass as general and sugars made in the abstract ection? "Unfortunately, severe conditions for complete conversion of carbohydrate inside the biomass structure are necessary, especially compared to the conversion of sugar compounds."

We have made the change suggested by the reviewer.

13) line 369, Temperature, time etc are not conditions, they are parameters

We have made the change suggested by the reviewer.

            We believe that the concerns of the reviewers have been adequately answered, and hope that the work may be published in Energies Journal.

                        Sincerely yours,

                        PhD candidate Pablo J. Arauzo

Round 2

Reviewer 1 Report

The comments were addressed correctly and the article can be published as it is

Reviewer 2 Report

THe manuscript has bee significantly improved and can be accepted for publciation