Lignocellulosic Agricultural Waste Valorization to Obtain Valuable Products: An Overview

Round 1

Reviewer 1 Report

The article covers the main biofuel and bioproducts that are being produced from lignocellulosic waste.  However, the article is mainly descriptive.  The article should provide a synthesis of the state of the art related to productivity, yields, and operating conditions. 

 

It is important to have a section informing about the degree of development of the technologies. Are those technologies applied on a commercial scale? What is the current status of the scale-up process?. 

The economic and environmental aspects should be discussed for all bioproducts, not only for biofuels and bioenergy.

Specific comments:

The abstract must inform about the contents of the article. The current version is similar to an introduction.

Introduction

L 32 This sentence is confusing and it does not provide scientific information: “ Planetary evolution in recent years has led to the emergence of some problems now shared by all the countries of the world in what is a real globalization of the challenges we are facing. Climate change, respect for the planet and the environment as suppliers of essential services for our survival, and the unsustainability of a development model based on the indiscriminate consumption of any resource is giving rise to growing efforts to find ways to make ends meet with the seemingly impossible.”

 

This sentence is also confusing: “is giving rise to growing efforts to find ways to make ends meet with the seemingly impossible”.

 

L 37 “A central element of the strategies being implemented in many countries around the world revolves around the growing use of renewable raw materials as a way out of a development model based almost exclusively on non-renewable resources [1, 2].”  The information in this sentence must be specific, what kind of products are produced mainly from non-renewable resources?. Currently, not all the production systems are based on non-renewable resources as claimed but this sentence.   References 1 and 2 were cited as support for this sentence. However, those articles are focused only on the use of lignocellulosic biomass for the production of fuels.

 

L 39 Define “EU”.

 

Figure 1 is not informative, it contains the same information written in the text. It must be removed.

 

L 173 change “par” for “per”

 

Table 3. It is important to mention the culture conditions generally used, such as temperature, pH, fermentation time

 

L 316 Cellulose was abbreviated (LCC), this abbreviation was only used in what section of the article and is not necessary.

 

L 340 This sentence lacks a reference, and needs more development. “However, at lower concentrations furfural has an inhibitory effect which becomes stimulating at high concentrations, therefore the addition of furfural optimizes biomethane production”

 

 

2.6 Economic and environmental considerations. This section does not include information about the state of the art of scientific studies related to LCA of bioenergy from lignocellulosic biomass. Which impact categories are more affected? Which strategies of lignocellulosic biomass utilization were more viable and sustainable according to scientific studies?. Why were not discussed economic and environmental considerations for the bioproducts in section 3?

 

L786 [BMIM]HSO4, since BMIM is an abbreviation the complete name should be mentioned the first time. The subscript must be used for the chemical formula.

  

L789 reference 318, what is the conclusion? Why was it a novel system, why it was better than other systems?

 

L805 the supercritical CO2 extraction. The subscript must be used for the chemical formula.

 

L914 micro-organisms. It should be a single Word.

 

4. biopolymers.  The introduction mentioning heavy metals is out of context. It should be removed.

 

 

Minor revisions are required. 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

In this manuscript, the authors present a review of potential valorization routes for lignocellulosic biomass. Special emphasis is given to agricultural residues. In general, this review is thorough, covering a wide range of topics in moderate detail. The various sections appear to be well-referenced, and I presume that this manuscript would be a useful starting point for a wide audience of interested readers. My primary remark about the manuscript is that it is rather lengthy, and at times redundant, in which it seems like different coauthors wrote different sections without any significant effort to make them all come together cohesively. It may be helpful to approach a revision from a broad scope, with the aim of efficiently presenting details while keeping brevity in mind. Please see below for a few additional remarks:

Line 48: Please add references to any relevant literature and/or policy, if possible, that provide details about the “Waste Framework Directive (WFD)” as a whole (for example : https://environment.ec.europa.eu/topics/waste-and-recycling/waste-framework-directive_en).

Figure 1: It looks like the red “spell check” underlining from software used to create this image is still present as an artifact in the figure.

Line 77-78: This description of cellulose is not quite right – I don’t think its conventional to refer to cellulose structures as aromatic. Also, the term “cellobiose” typically refers to a dimer (2 glucoses), so it’s unclear how this fits into the text describing cellulose.

Figure 2: Please consider adding a brief introduction/description of this figure in the text, before its appearance in the text (and in general, for all figures, where relevant).

Line 172: When making a claim that something is “undoubtedly” true, it may be beneficial/necessary to provide some quantitative evidence or cite references to relevant literature for support of this statement.

Line 202-211: This description is cellulose, hemicellulose, and lignin is a little bit redundant relative to what has already been presented earlier in the text. Please consider revising for more brevity here.

Line 315-320: It’s unclear what the acronym LCC is describing here – is it for lignin-carbohydrate complex? If that is the case, then putting this after cellulose isn’t quite right. This paragraph itself is also a little redundant relative to earlier text.

Line 384-394: This part is redundant, for example, in comparison to information already presented in table 2.

Line 686: It may be helpful to briefly list here a few key metrics for quantifying environmental impact, for example, CO2 emissions, global warming potential, waste generation/pollution, etc.

Line 838-839: It’s a little unclear here what this is trying to say, as it sounds like the lignocellulosic biomass itself is being converted into enzymes, rather than lignocellulosic biomass being used as a substrate for enzyme production by microorganisms. Please consider revising for better clarity.

Table 4: I’m not sure that this table is entirely necessary to include, given the context of this manuscript, and it may just be better to have a list of references after the first sentence in line 976.

Figure 3: Please be sure to include any references to relevant literature that was used to make this figure.

Line 1073: The first sentence of this section is not necessary and can be removed.

The manuscript would benefit from an additional, thorough proofread to verify that English language/grammar is OK. I did not find any issues that affected reading comprehension for the text as presented.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The article was modified according to the suggestion made in the first Review.  The abstract explains the content of the article, new sections were added for the life cycle analysis, the degree of development of the technology, and economic perspectives.  Also, the culture conditions and information about yields and productivity were included.

Please revise the chemical formula for CO” on lines 721 and 727 since the number 2 is not with a subscript.

Reviewer 2 Report

Thank you to the authors for their diligent efforts in revision. This should be acceptable, provided that all other reviewer's remarks have been adequately addressed, and there is additional, minor editing for English language and review of accuracy for references to relevant literature.

Overall there are no serious issues, although the manuscript could likely be "improved" but additional review for word choice and grammar.