Composting Hydrochar-OFMSW Digestate Mixtures: Design of Bioreactors and Preliminary Experimental Results

Round 1

Reviewer 1 Report

In line 60, There is a lack of description of the scheme of the bioreactor.

(ex. the term description about T air, T max, etc)

Author Response

please refer to the attached file

Author Response File: Author Response.pdf

Reviewer 2 Report

Interesting article of scientific and industrial utility. The methods used are very well explained and the article is easy to follow. Figures and tables are very useful to understand.

However, I propose to the authors some improvements:

Figure 1: Please explain what are the acronyms that are put in the diagram (T air, T mix, P).

Table 5: the values in this table are very similar to those in table 4. If they are the same, they should not be repeated and if they are different, the difference should be explained

Conclusions: I think it should be explained what advantages this type of composting has with respect to traditional composting. Is there any advantage?

Author Response

Please refer to the attached file

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript entitled "Composting Hydrochar-OFMSW Digestate Mixtures: Design of Bioreactors and Preliminary Experimental Results" deals with the desig and operation of a composting reactor for the composting of hydrochar and OFMSW digestate mixtures.

The topic is interesting for the applied sciences readers an I consider that it coul be published after several moficications:

1. The introduction should present some information about the state of the art of the composting bioreactors design whith the aim to inform the readers about its current state and which were the developments achieved in the research carried out.
2. More information about the respirometric methods should be included. Several references dealing with this topic are the following:

   Bermudez, J.F., Saldarriaga, J.F., Osma, J.F.
   Portable and low-cost respirometric microsystem for the static and dynamic respirometry monitoring of compost
   (2019) Sensors (Switzerland), 19 (19), art. no. 4132
   DOI: 10.3390/s19194132

   Ruggero, F., Gori, R., Lubello, C.
   Methodologies to assess biodegradation of bioplastics during aerobic composting and anaerobic digestion: A review
   (2019) Waste Management and Research, 37 (10), pp. 959-975.
   DOI: 10.1177/0734242X19854127

   Adhikari, B.K., Trémier, A., Barrington, S., Martinez, J.
   Biodegradability of municipal organic waste: A respirometric test
   (2013) Waste and Biomass Valorization, 4 (2), pp. 331-340.
   DOI: 10.1007/s12649-012-9135-5

   Binner, E., Böhm, K., Lechner, P.
   Large scale study on measurement of respiration activity (AT4) by Sapromat and OxiTop
   (2012) Waste Management, 32 (10), pp. 1752-1759.
   DOI: 10.1016/j.wasman.2012.05.024

   Sánchez Arias, V., Fernández, F.J., Rodríguez, L., Villaseñor, J.
   Respiration indices and stability measurements of compost through electrolytic respirometry
   (2012) Journal of Environmental Management, 95 (SUPPL.), pp. S134-S138.
   DOI: 10.1016/j.jenvman.2010.10.053

   Barrena Gómez, R., Vázquez Lima, F., Sánchez Ferrer, A.
   The use of respiration indices in the composting process: A review
   (2006) Waste Management and Research, 24 (1), pp. 37-47.
   DOI: 10.1177/0734242X06062385

   Gómez, R.B., Lima, F.V., Bolasell, Ma.A.G., Gea, T., Ferrer, A.S.
   Respirometric assays at fixed and process temperatures to monitor composting process
   (2005) Bioresource Technology, 96 (10), pp. 1153-1159.
   DOI: 10.1016/j.biortech.2004.09.026

3. Authors should indicate how was calculated the theoretical thermal profile of the industrial plant (Data presented in Figure 4).
4. Taking into account the title of the manuscript,"Composting Hydrochar-OFMSW Digestate Mixtures: Design of Bioreactors and Preliminary Experimental Results" I suggest the authors to include in the main body of the manuscript some of the information presented in the Appendixes, mainly those related to the reactor design.

Author Response

Please refer to the attached file

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors, 

I have read Your manuscript entitled "Composting Hydrochar-OFMSW Digestate Mixtures: Design of Bioreactors and Preliminary Experimental Results" and it should be interesting for readers, but some improvements should be done:

1. Please add results information in Abstract.
2. Please do not repeat words from the title as "keywords".
3. The Inroduction section should be expanded to include literature rewiev in field of composting/OFMSW oxygen stabilziation, including process parameters, i.e. doi: 10.1007/s12649-019-00831-6; as well as HTC  doi.org/10.3390/en13010262
4. Line 29- please add reference to confirm statement.
5. The novelty of research should be emphasized. i.e. the reactor design, process control based on on-line DRI, HTC addition verification. 
6.  Please add information (manufacturer, model , country) of used equipment in the study, i.e. membrane pump, zirocnia probe, oven, muffle, etc.
7. Lines 193-211 should be rather removed to discussion section. As well as lines 241-246. While lines 273-283 should belong to results section.
8. Lines 269-270- the units should be added.
9. The discussion has to be expanded. The comparision to others research results should be done. Lines 241-246 Authors stated that the lower moisture limits microbial activity, but what happens if moisture is too high- the air flow is disturbed. Similarly, lines 138-141- the density of the blank mix was determined- what about other feedstocks?, what is the impact of inproper density on composting process.
10. Only one internal mixing was implemented: please describe, i.e. include citations, refer the possible turning impact on compostiong process.
11. In my opinion base on the study results some optimal composition of co-composting feedstock should be chosen and justified.
12. The figures and tables names should be reviewed- are to long and confused reader, please verify simplification, i.e.: Fig.2: The bioreactor construction; Fig. 3. The designed bench-scale bioreactors; Fig. 4. The temperature profiles during composting process, etc. Tab. 1. Characterization of the biomass before and after carbonization; Tab.2. The feedstock composition of composting process; etc. Please also use full names (not abbreviations) in tables - to constituate a whole separate.
13. The conclusions should be linked to the aim of the study- please verify and review the conclusions (HC proportion, TS, VS, DRI values, optimum condition/compositon) or review the aim of the study.

Author Response

Please refer to the attached file

Author Response File: Author Response.pdf

Reviewer 5 Report

This work deals with the development of a bench scale bioreactor for organic municipal wastes composting. It aims to solve a big problem under the spirit of the cyclic economy. Moreover, if this trial will succeed the environmental fingerprint of this work will be positive. Despite the fact that many research efforts were carried out on this topic untill now and many applicable results are already published,  the paper is well written the idea is very good. I suggest to be published as it is.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The paper can be accepted once solved the error generated by the reference manager software on lines 111, 116, 119 and 145 where the software indicates "Error! Reference source not found".

Reviewer 4 Report

Dear Authors,

thank You for reviewed manuscript having previous comments and consider some details:

Please verify "errors" which appeared in lines 111, 119, 120, 146. 

Line 290- "Figure 8" is repeated.

Please verify again and add information (manufacturer, model , country) of used equipment in the study- i.e. line 175- oven, muffle.

Round 3

Reviewer 3 Report

Under my point of view the paper can be acepted.