Modelling of Amino Acid Fermentations and Stabilization of Anaerobic Digestates by Extracting Ammonium Bicarbonate
Round 1
Reviewer 1 Report
Title - Flash distillation process for stabilization of anaerobic digestate and synthesis of ammonium bicarbonate.
The manuscript by Abelenda AM et al. is interesting and well-presented. It requires revision before its publication as follows:
Comments
1. Introduction (Paragraph, 1), the details about AD for waste management, its process, microbes, and major advantages/disadvantages should be added. Further, AD uses to develop biorefinery approaches for value-added products i.e., Renewable and Sustainable Energy Reviews 150 (2021) 111491.
2. In Figure 1, please add a summary of the findings with quantitative data or mass balance details.
3. The discussion section can be minor improved, and also provide information on the microbial perspectives of AD in the generation of digestate.
Minor editing of English language is required
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article is aimed at studying the flash distillation process for stabilization of anaerobic digestate and synthesis of ammonium bicarbonate by mathematical modeling, which can lead to a reduction in the cost of physical modeling of the studied processes, which are generally quite relevant. However, despite the relevance of the processes under study, the design of the article raised a number of questions. Therefore, I recommend the major revision.
Key comments:
1. There is no description of the inoculum used in section 3.3 in the text of the article.
2. The article does not contain a description of the operation of the fermenters indicated in section 3.3 (I can’t indicate the page and line, because the article is not formatted according to the template).
3. Figure 1 is not very clear: in the introduction at reference 12, stripping of ammonium with biomethane was described. Is this drawing an extension of the stripping idea? The figure does not show all the flows and does not describe the elements of the production line. Is biogas removed from the fermenter? If so, where does the improved biogas come from at the end of the process?
4. It is not clear on what basis moisture content of the digestates was selected and how it was determined.
5. In general, the materials and methods section needs to be significantly improved.
6. The conclusion is somewhat unsound: what is the criterion by which this study confirms the suitability of the flash distillation conditions?
7. How will the stabilized digestate with unreacted titrant be used?
8. There is no assessment of the adequacy of models.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors presented a work on a model in Aspen Plus v12 in order to predict the best settings for recovering nutrients from an anaerobic digestion process by a flash distillation step. The main goal of the study is to recover ammonia and carbon dioxide by synthetizing ammonium bicarbonate. First of all, the title of the paper is deceiving, since there is no word which indicates that this manuscript describes a model in Aspen Plus v12. Therefore, I'm suggesting to change the title to be more appropriate.
The goals are ambitious but the results and conclusions are clear and interesting. What has to be improved are the presentation of the experiment and the methodology. The introduction is hard to read due the complexity of the explanation of the patented ABC and the distillation process engineered by Drapanauskaite et al.. For this reason, I'm suggesting to rewrite those parts, maybe being more superficial but more understandable. Furthermore, it is not clear how the k equation was determined, it should be specified.
Moreover, Fig 5. Would be more helpful to have the same scale axis (for both of them i.e., pH and kg NH4HCO3/h).
Fig 6. If water is omitted in graph b it should be omitted in graph a as well in order to have a clear picture of the most relevant species.
Fig. S3 graph do not have the same axis scale, which makes them hard to compare and, the last three graphs are cut so it’s impossible to read the x axis (time) and the letters which indicate the amino acid.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
The article is very interesting but moderate improvements are required. However, some more details of the methodology and aim of their selection are needed. The error and regression methods are not presented clearly. Please add more detail to show the visible replicability of the research.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Accept
Reviewer 2 Report
The authors have done a great job both in writing the article and in eliminating its shortcomings. At the same time, the article touches upon the current research topics with an original approach, and therefore I recommend accepting the article for publication in its present form.
Reviewer 3 Report
The authors have responded extensively to all my inquiries. The paper is now ready to be published in Fermentation.
