Wood Ash Based Treatment of Anaerobic Digestate: State-of-the-Art and Possibilities

Round 1

Reviewer 1 Report

Manuscript Number: processes-1534526

Title:” Treatment of the anaerobic digestate with wood ash: State-of-the-art and possibilities”

The paper focuses on the valorization of wood ash and anaerobic digestate for the preparation of a slow-release fertilizer.

 

The manuscript is well written, generally understandable and readable.

However, below some suggestions and comments to improve the quality of the paper.

 

• L 59. Please, explain the reason of 7 billion tonnes of biomass production.

 

• L 607-700. Your manuscript investigates the feasibility of manufacturing granular fertilizer based on blends of ash and organic manures. However, many authors highlighted that organic fertilizers are produced in pelletized form with several advantages. In my opinion, also this kind of densification process, to produces densified organic fertilizer, should be discussed in this paper. Below some references focused on this topic:

J.R. Rao, M. Watabe, T.A. Stewart, B.C. Millar, J.E. Moore, Pelleted organo-mineral fertilizers from composted pig slurry solids, animal wastes and spent mushroom compost for amenity grassland, Waste Manag. 27 (2007) 1117-1128.

Alemi, M.H. Kianmehr, A.M. Borghaee, Effect of pellet processing of fertilizer on slow-release nitrogen in soil, Asian J. Plant Sci. 9 (2010) 74-80.

Zafari, M.H. Kianmehr, Effect of temperature, pressure and moisture content on durability of cattle manure pellet in open-end die method, J. Agr. Sci. 5 (2012) 203-208. doi: 10.5539/jasv4n5p203.

Pampuro, G. Bagagiolo, P.C. Priarone, E. Cavallo, Effects of pelletizing pressure and the addition of woody bulking agents on the physical and mechanical properties of pellets made from composted pig solid fraction, Powder Technology 311 (2017) 112-119.

• Figure 8b. This Figure is not related to the solid fraction obtained after solid liquid-separation. Please, verify.

Author Response

Please  find responses in the attachment file

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors did a lot of work describing numerous processes and systems and analyzing 158 literature items. All the work seems logical. Unfortunately, there is a problem with the conclusion. It was written "The minimum share of anaerobic digestate in the blend with the WA would be virtually 0 % w/w, for the manufacturing of a granular fertilizer with the greater mechanical properties (e.g. compressibility strength, durability, etc.)". And yet the Authors are looking for ways to use WA. Please explain this.

Author Response

Please see attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The article entitled “Treatment of the anaerobic digestate with wood ash: State-of-the-art and possibilities" presents an overview of the literature data on the chemistry of mixtures of anaerobic digestates and wood ash to prepare a new fertilizer.

General note

Main weakness

The authors reported that the aim of the study was to seek an energy-saving method of processing anaerobic digestate into fertilizer using wood ash. The presented literature data did not allow the authors to achieve the goal. Therefore, the statement "a process that requires less energy" should be removed from the aim.

 It is also not known why the optimal dose of WA suddenly appears in the conclusion, which, according to the authors, is 5 g TS ash/g TS digestate.

I read the manuscript with great pleasure. The subject of the study is very interesting and topical, with scientific and practical importance. The data presented are of more than national interest.

The introduction is presented correctly, in accordance with the subject. Numerous scientific articles, in concordance to the topic of the study, were consulted.

The scientific literature, to which the reporting was made, is recent and representative in the field.

There are some minor changes I am suggesting in detailed comments below.

Specific comments 

Line 14 - The abbreviation " TS " appears in the work for the first time - it should be explained.

Line 60 – there is: “minion tonnes” ?

Table 1 – row 4 – there is: “Lo et al. (2010)” - please correct the reference

Lines 123 – 127 The information contained in this section, i.e. the HRT and OLR formulas, is redundant.

Line 278 – there is: “Pesonen et al. (2016)” - please correct the reference

Line 432 - The abbreviation " WBA " appears in the work for the first time - it should be explained.

Line 446 – wrong format

Line 493 – wrong format

Line 497 - The abbreviation " WS " appears in the work for the first time - it should be explained.

Line 550 – wrong format

Table 3 - The abbreviation " COD " appears in the work for the first time - it should be explained.

Author Response

Please see attachment

Author Response File: Author Response.pdf