Evolution of Microbial Composition and Enzymatic Activities during the Composting of Textile Waste

Round 1

Reviewer 1 Report

The manuscript presented by Biyada et al reports on the composting of textile waste, whose results highlight the production of stable and mature compost. Although the present study is of high interest, I regret to inform the authors that I do not support the publication of this study on the journal Applied Sciences in the current form for several reasons, which are finely disserted below.

 

English language needs to be extensively improved, as the current version of the manuscript impairs a proper fruition of the study by a smooth read.

 

Lines 53-54: the amount and variety of microorganisms are not important parameters. Microorganisms are the biotic reason on which is based the composting process.

 

Lines 58-59: Nutrients cannot be made usable my microorganisms, as the latter can utilize complex carbon sources depending on the microbial catabolic repertoire.

 

Lines 59-60: “The enzymatic activities result from the bacteria (including the actinomycetes) and fungi that are directly involved in organic matter degradation.” Alternatively, I wonder from where enzymatic activities should come.

 

Line 63: Intervention? It would be better stating microbial-based process?

 

Line 65: The molecular phylogenetic study does not estimate what the authors wrote.

 

Lines 66-68: “Therefore, for a complete analysis of microbial populations in the environment, a metagenomic approach using direct DNA sequencing in order to avoid the loss of diversity related to cultivation is used.” Hard to read text. In this context would be better to focus on the object of this study. The statement “using direct DNA sequencing” implies that given a sample it would be directly sequenced, instead, metagenomics DNA must be isolated first. “To avoid the loss of diversity” of what? Too many things given for granted, impairing the fruition of the study for scientists that do belong to related research fields.

 

Lines 71-72: “conventional DNA sequencing techniques” what these might be?

 

Line 76: microorganism composition or microbial composition?

 

Line 79: I do not see the point to address actinomycetes and fungi, total microflora has only one meaning.

 

Line 82: The overall goal of the study is missing.

 

Line 147: Without rotor information 10,000 rpm has no meaning.

 

Line 148: By using 0.45 μm filter it cannot be ruled out the presence of microbial cells. So, I would not write about enzymatic extract.

 

Lines 180-185: There is a table for all these valuses, which is more ordered than the text. I suggest readjusting this part as it is hard to follow.

 

Lines 188-194: “Peaks with the bands of respectively 3440, 2919, 2850, 1400 cm^-1(Figure 1) are 189 characteristic of crystalline cellulose, hemicelluloses and lignin…” respectively to what? all these bands indicate crystalline cellulose, hemicelluloses and lignin or some of them? 2919 cm^-1 might be ascribed also to CH₂asymmetric stretching, therefore the majority of organic molecules share this feature, as well as macromolecules (i.e., lipids, carbohydrates ect.). 2850 cm^-1 can be ascribed to CH₂symmetric stretching, which is not typical of crystalline cellulose, hemicelluloses and lignin sensu stricto. If the authors want to prove their point, they need to test standards as well. 2919 and 2850 cm^-1 might derive from waxes present on the surface of the plant cell wall, which is highly probable considering the provenance of the textile waste investigated. 1400 cm^-1 can be ascribed to CN stretching, NH rocking, CO stretching, therefore I suggest the author to be more conditional, avoiding stressing the real lignocellulosic nature of what they are observing, as the object of this study is of complex nature. 1631 cm^-1might be C=O stretching typical of diverse molecules of organic nature. I do not comment the others, I believe I made my point. So,

I suggest improving the literature search for the IR analysis, including a table reporting what can possibly be ascribed to vibrational modes observed, which would result easier to read and more informative.

 

Lines 229-237: The pH of mix B it does not increase after 9 weeks, it slightly increases after 28 weeks, plus, is there any statistical significance for these observations? No statistical information is provided. Same observation for the electrical conductivity, as the increase of the latter is evident for mix mix A and B, while for C this value is slightly above, at the end-point, as compared to that recorded at the very beginning of the experimentation. Are these differences statistically valid?

 

Line 266-onwards: I do not understand the reason why actinomycetes are left aside the overll bacterial cell count evaluation. Is there a specific reason?

 

Line 284: How the authors can be so sure that cellulose activities depend only on those that were secreted?

 

Lines 292-298: Can the author comment on the different behavior of phosphase acid activity, which differently reaches its optimum as compared for all other parameters evaluated in this study?

 

Line 309: “…This compost harbours a wealth of different microbial species…” What compost? A, B, or C? Moreover, it is not reported on which bases the authors decided to analyze compost B by NGS.

 

Line 350: physico-chemical or physicochemical, please make your writing consistent by choosing one terminology.

 

Lines 353-355: Again, given the complex nature of the sample investigated in this study, I would be careful in stating with absolute certainty that the vibrational modes detected by IR spectroscopy unequivocally indicate the lignocellulosic nature of the waste.

 

Lines 355-357: These results suggest that the nature of the waste might be rich in lignocellulosic material among others unidentified things.

 

Lines 361-362: Can this aspect be due to the physiological cell turn over, as well as to an actual death of bacterial and fungal cells, which, releasing cell components, might contribute to the overall increase of nitrogen content?

 

lines 378-381: I hardly believe that there is only one mechanism going on, as well as pH, temperature moisture, and electrical conductivity do not evaluate such hypothetical microbial mechanism. The above-mentioned parameters influence, instead, biotic processes.

 

Line 381-391: This part of the discussion is hard to follow.

 

lines 392-399: Could the disappearance of metals be linked to the synthesis of biogenic nanomaterials? This question arise as bacteria are not only capable of performing biosorption phenomena. As a matter of fact, bacteria can bioaccumulate metals within the cells, reducing metals to a less toxic valence state generating nanomaterials or simply biomineralizing them. Moreover, Metals can be biotically chelate through EPS and/or siderophores that are not even mentioned. I found extremely reductive to ascribe metal disappearance just to adsorption or absorption phenomena. Authors need to address better this part of the discussion.

 

Line 417: “Durant”?

Author Response

s'il vous plaît voir la pièce jointe

Cordialement

Author Response File: Author Response.docx

Reviewer 2 Report

General comments

As a general remark, the results are of interest for the readers of MDPI Applied Sciences .

 

The authors presented topic results concerning the compost production using three waste mixtures (textile waste mixed with either green, paper & cardboard waste). In this paper authors shoved the characteristics of microbial communities and enzymes activity changes during the compost processes. The use of textile waste mixed with either green, paper and cardboard waste in the composting process is an interesting way to valorize these wastes in the composting process.

To my knowledge, there are few works showing the use of such waste in compost production. The work is well presented and well written. The subject is of interest and in the scope of the journal.  The abstract is clear and correct in summarizing the paper. The all needed methodology procedures are written correct. The obtained results are commented very well. The figures and tables are necessary and correct. Discussion is written deep and authors cited the publication from the last decade.

 

However, in several cases, presentations/assumptions/conclusions of the authors are not correct and need modifications/enrichments/revisions. Precisely:

1. Page 14, line 357 - please add information, than unconventional keratin waste such as pig bristles in the mixture with sawdust and lignite can be successfully used in the composting process, where the addition of keratinolytic Bacillus cereus was used.

 

Choińska-Pulit A., Łaba W., Rodziewicz A. Enhancement of pig bristles waste bioconversion by inoculum of keratinolytic bacteria during composting. Waste Management. 2019, 84, 269-276.

 

 

 

Author Response

Please see the attachment.

cordially

Author Response File: Author Response.docx

Reviewer 3 Report

The authors analyzed in detail the trend of the composting of textile waste mixed with green, paper & cardboard waste in different proportions, from a chemical-fiscal and biological point of view. Even if textile wastes are recalcitrant, a good composting was obtained even when the presence of textile waste was predominant. Since composting is a biological process, knowing the microbial activity of the various microorganisms involved and the enzymes referable to them is of fundamental importance for optimizing the composting process. The keywords are adequate. The experimental design is good and there is a wealth of data shown which, however, are not adequately valorized in the discussion phase, so that the novelty and originality are only intuited by the reader but never fully expressed by the authors. The introduction must also be expanded to better focus attention on the issues studied. Finally, there is no correspondence between what was stated in the introduction (lines 75-77) and what was discussed in the manuscript.

Based on these considerations, a revision of the introduction and discussion is suggested as shown below.As well as, should be performed an English revision.

 

MAJOR ISSUES

Please avoid using the plural first-person form. Replace all references to "we", "our" etc. with impersonal forms.

Please edit in a better way the text and the figures, in particular Fig. 2, 6, and 11 which must be made more harmonious in their proportions, for the text to separate the various paragraphs uniformly.

The introduction should be expanded by highlighting the problems that the manuscript intends to study and at what point is the knowledge on this topic to better highlight the novelty proposed by the authors.

The discussion should be expanded by using NGS to explain the results obtained through the microbial activity of the microorganisms identified.

par. 2.7 Please indicate which samples were processed with NGS and why. The text shows that only the mixture "B" has been analyzed and only at the end.

P7 L205 there is no correspondence between 1.35% for "B" reported in the text and the table. Please correct.

P7 L208 Please check the reported values.

Fig. 5 Please highlight the significance of the differences.

Pag 12 L305-311 Please move this part in the discussion after line 423.

Pag 13 L320-324 Please move this part in the discussion after line 433.

Fig. 10 Which sample are the authors referring to?

P 14 L 333 Please clarify the sentence.

P14 L 342-344 Please move this part in the discussion after line 423 and combine it with the text reported between L305-311.

P14 L350-355 Please rephrase not as if they were conclusions but as if it were a starting point confirming your assumptions about the good quality of the mixtures in exam.

P15 L359 Please add the number of values about decreases.

P15 L365-366 Please check the sentence: the C/N ratio should be increased (as reported in Tab.2 in the middle stage) due to ammonia volatilization. Then the authors have to rewrite the next sentence writing that finally, the consumption of C causes a lowering of the C/N as indicated by several studies that related this parameter to maturity degree.

P15 L386-388 and L401-407 Please discuss the difference in electrical conductivity of "C" compared to "A" and "B" (Fig.3). Can this difference be linked to a lower GI index (Fig.5) in "C" and is the latter significant difference?

P15 L392-399 Please discuss the lower Zn removal in “A”.

P16 L442-444 Please rewrite the sentence: NGS has not shown that many species are involved in the degradation of cellulose, but has shown that in the compost samples there were many species belonging to phyla capable of degrading cellulose.

In consideration of this, the discussion should be expanded because the mixture "B" has shown some peculiar results: more CFUs in total microflora population which are not fungi or Actinomycete since they are very similar to "A". And also persistence in the activity of cellulase. Use the evidence of the NGS to discuss these particular results.

P16 L476-486 The mixture "B" showed a higher acid phosphatase than the others up to 30 days. The authors declare that fungi produce high amount of acid phosphatase. Since there are no quantitative differences in the fungal population (Fig. 6) can this result be justified by the greater amount of total microorganisms typical of the mixture "B" in the focused period? You can broaden the discourse of L479-481 for this topic.

The first part of the conclusions (L493-497) should be moved to the end. The conclusions need to be rewritten better because they are disordered. Among the phyla identified with NGS, those involved in the composting process and what they are involved in must be said.

L502-504 Please add the% of textile waste that gave the best results in terms of compost.

 

MINOR ISSUES:

 

L22 Please avoid reference to the names of mixtures A and B because the reference is missing in the text. Rather, replace with "the 2 best mixtures showed C/N ratios...".

L36 Please add a comma before “today”.

P2 L63 Please replace “intervention” with “activities”

P7 L206-207 Please rephrase as suggested “Due to a nitrogen concentration increase and a decrease in organic carbon, during composting, a decrease in the C/N ratio was observed”

P7 L210 Please remove “between”.

P10 L258 Please remove “(g^-1)”

P11 L286 Please replace “paralleled by” with “consequent to”

Author Response

Please see the attachment.

cordially

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The manuscript is now scientifically sound and represents something that I enjoy reading. However, I strongly recommend checking the manuscript for English grammar.