Increasing Biomethane Production in MSW Anaerobic Digestion Process by Chemical and Thermal Pretreatment and Process Commercialization Evaluation
Round 1
Reviewer 1 Report
OFMSW: please write out the abbreviation the first time you use it. OFMSW is not a generally understood abbreviation.
l. 50 lignin is not removed but the individual fractions are separated from each other so that it is easier to degrade the individual fractions. However, lignin is still present in the sample/biomass.
l. 51 – 53: what are the results of the investigation?
l. 54 – 56: what are the results of the investigation?
L. 57: what are the results of the investigation?
L60: maximized the biogas yield? Please add the numbers: how many ml of biogas are in the untreated sample? the absolute and relative effect of pretreatment on biogas/methane yields, degradability of biomass.
L 61: an economic perspective: what exactly was done? This aspect is relevant in this position since a higher methane yield alone does not improve an economy.
L 63: why METHANE is written in capital letters
L 62 ff: what are the outcomes, and what influence does the pretreatment have on the results?
l. 64: what exactly was examined, and what are the outcomes?
L. 66ff. it seems that it is a rewording of the abstract of the paper
l. 73: Ref 20: “The optimum hydrothermal condition was 170°C at 4 g NaOH/ 100 g solid for one hour.” The author writes previously that temperatures up to 110°C make sense. The two paragraphs conflict with each other
l 75: crystallinity from what? Cellulose? Important data are missing: The crystallinity of the ingredients is strongly influenced under certain conditions, it is a question of the pre-treatment methods used in the trials. It needs all the information on what exactly this statement refers to. In this way the statement is wrong
l 75 ff: this statement is not true in all cases. Detailed information must be included
l 78: what exactly was done, and what did the named tests yield?
L 88-94: new topic, which is however only treated very superficially. Delete it
L150: The authors 150 subjected 50 kg of the waste to an oven at 70˚C for a minimum of 24 h. Please add why this was done.
L154: …was crushed using a mill… Milling is significantly influencing the specific biogas yield. Also, the effectiveness of the pretreatment is influenced by it. Please analyze and report the effect of the milling in comparison to the untreated sample
L157: Please analyze and include the content of volatile substances. Alternatively, the water content according to the Karl Fischer method or a wet chemical determination of the COD (no calculation from the elemental analysis).
@ 2.6 Economic as well as 2.7 Biogas upgrading simulation: analysis of the process: no comments on this part as I am not an expert on this topic
L223: Results of chemical analyses of untreated and pretreated samples have to be done and included in the article.
L 239: it is not an “unpretreated specimen”—pre-treatment by separation, crushing as well as grinding of the sample.
@ 3.2: number of replicants is missing, standard deviation or min max values must be added to the results
Table 3: The table is not essential. Results are shown in the text
L373 -381: speculative, must be deleted incl. fig. 5
3.5, 3.6 (L 413 -605): There is no added value in calculating these results for me. These are pure simulations and assumptions, which are not necessary to evaluate chemical experiments. The entire section should be deleted, corresponding adjustment in the abstract.
Author Response
Dear reviewer
Thanks for reviewing the manuscript. Answers to comments are provided in the attached PDF file.
Sincerely.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article is very interesting particularly the techno economical analysis of different anaerobic digestion scenarios. The major pitfall, from my perspective, is that it tries to cover too many different aspects and some of them are a bit superficial. I suggest shortening the document so that ii can be easily followed and understood. My suggestions/correction are presented next:
Introduction
The introduction should be shortened. For instance, the first two paragraph are too general, delete them.
A paragraph explaining the type of reactions that take place when H2O2 and NaOH are mixed with the substrate should be added. It is good to understand why these compounds help to increase the anaerobic biodegradability of the substrate and why they were chosen for the present study
English must be revised by a native speaker. It is even difficult to follow in some parts. For instance, the word specimen is used instead of sample. I never heard this word before within a research study context
Throughout the document the term biomethane is used as if it were biogas. Biomethane is normally used to allude to the result of the process of biogas upgrading. Revise
Material and method
Page 3. Line 104. Those “early works” that are mentioned should be cited
The conditions of the thermal pre-treatment are “mild” compared to those typically employed, for instance, in a Cambi equipment. Discuss
Describe the software that was used for the biogas upgrading simulation
Results
It is not clear to me what kind of control test was considered in the study. Add it to Table 2
How was the Methane yield (Table 2) estimated from the BMP test? Explain
Why does “y” in eq 1 is to the power of -1.97? It does not make much sense to me.
Figure 1 is a bit meaningless if it is the same data that was used to build the polynomial models. Consider deleting it or putting in as Supplementary material
Figure 4 should be placed before
Figure 5 should go to supplementary material or be removed from the document
How is soluble COD (SCOD) measured for such a solid substrate? The SCOD and VS reduction are referred to the effect of pre-treatment or the BMP test?
Table 6 or 7 can be relocated in the Supplementary material section
What is the fate of the biogas in scenario 5 (Table 10)? Why not considering a CHP unit?
Author Response
Dear reviewer
Thanks for reviewing the manuscript. Answers to comments are provided in the attached PDF file.
Sincerely
Author Response File: Author Response.pdf
Reviewer 3 Report
This study explored the effects of anaerobic digesters with chemical and thermal pretreatments on biomethane production. RSM was used to optimize the two modes of utilizing H2O2. The optimal conditions for biomethane production were obtained by comparative analysis of experimental results. The different application scenarios of biogas digester are analyzed comprehensively. This paper is the first to study the effect of anaerobic digestion using both thermal alkaline and H2O2 pretreatment to produce biogas, which is a novel research content in this paper. However, the selection of parameters in the experimental process and the experimental data should be better presented to increase readers' trust in the experimental results. Some supplements and modifications to this article will be more conducive to publication.
Comments for author File: Comments.pdf
Author Response
Dear reviewer
Thanks for reviewing the manuscript. Answers to comments are provided in the attached PDF file.
Sincerely
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
No more comments
