Comparison of Alum and Sulfuric Acid to Retain and Increase the Ammonium Content of Digestate Solids during Thermal Drying
Round 1
Reviewer 1 Report
The paper deals with the drying of manure- and sewage sludge-based digestates and the influence of H2SO4 and aluminium sulphate addition in order to decrease ammonia nitrogen volatilization during the drying process. The paper opens a new way for acidification of digestates before the drying process which is often applied to reduce water content and to ease transportation.
Moreover, the paper is very well written, clear and well structured in every section. In my opinion, the discussion of results is very thorough and each conclusion is well justified. As a recommendation, other physical and chemical analysis could have been done in order to deliver more information regarding the reactions that took place when adding sulfuric acid or aluminium sulphate. This could have substantiated even better the author’s conclusions. In any case, this fact does not detract from the article.
The authors can find some suggestions below that may improve the quality of the paper:
#1. Line 39. Please, separate “alumas” into “alum as”
#2. Section 2.2. How long last the drying procedure? In the next paragraph, the authors stated a drying time of 200 and 170 mins for MDS and SDS based on a preliminary experiment, but it is not clear that these times were applied to this experiment. Maybe authors can rewrite both paragraphs to make it clear.
#3. Lines 90 and 91. What are the differences between the different treatments? Can you please specify in materials and methods the different concentrations of each reagent used? This might be independent of the explanation in Results and Discussion on how you decided reagents concentrations to be applied.
#4. Figure 3. Moisture loss is in bold, please correct it.
Author Response
Please see attached docx
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This study compared the additions of alum and sulfuric acid for nutrient (nitrogen and phosphorus) fixation during thermal drying of digestate solids. The writing is generally clear, but some grammatical mistakes are quite obvious. Readers in the fields of organic waste treatment and resources recovery will be interested in this work. It is recommended for major revision.
Some questions below need to be addressed/discussed:
- Schematic diagram would be useful readers to understand the experimental flows.
- The justifications of research gap and hypotheses are not well-organized/ logical. Please revise.
- One relevant reference of waste recovery is recommenced: "A critical review: emerging bioeconomy and waste-to-energy technologies for sustainable municipal solid waste management”
- The writing needs to be more precise. e.g. conclusions are too long and too descriptive; focus on verifying the hyothesis
Author Response
Please see attached docx
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Accept
