Pelletization Temperature and Pressure Effects on the Mechanical Properties of Khaya senegalensis Biomass Energy Pellets
Round 1
Reviewer 1 Report
Comments to Authors:
(1) Page 1, Abstract: Please include the results of pellets mechanical characteristics.
(2) Page 1 and throughout the manuscript: Citation format: ‘[1], [2]’ or ‘[1,2]’?
(3) Page 1, Line 36: In the Introduction section, the authors focusing on the local Malaysian fibrous plant species suitable for biomassic material. However, Citation 1 discuss about bioenergy in Finland. Please replace with suitable citation focusing on raw materials from Malaysia. Suggestion of reference ‘Co-fermentation involving Lysinibacillus sp. and Aspergillus flavus for simultaneous palm oil waste treatment and renewable biomass fuel production. AIMS Microbiology, 8(3): 357–371. DOI: 10.3934/microbiol.2022025’.
(4) Page 2, Line 46 and throughout the manuscript: Italicize the scientific name.
(5) Page 2, Line 51: In the Introduction section, please elaborate in-depth about the current reported pellet compactness value from published literature review/journals similar to raw materials of Khaya senegalensis.
(6) Page 3, Line 107: State the dimension of particle size. Example: ___ x ___ x ___ mm. In addition, please state the diameter of pellets utilized in this experiment.
(7) Page 3, Line 110: Specifically state the temperatures: 25, 50, 75, … °C.
(8) Page 3, Line 113: The authors use the instrument of Shimadzu Universal Testing Machine. State the maker’s city, and country. Example: Tokyo, Japan. All instruments utilize during research should state the equipment model, city, and country – Please check throughout the manuscript.
(9) Page 9, Line 329. Please include one more factor affect the mechanical properties of pellet, which is treatment of the raw materials. The authors are highly suggested to add this recent related reference: ‘Fermentation of Palm Oil Mill Effluent in the Presence of Lysinibacillus sp. LC 556247 to Produce Alternative Biomass Fuel. Sustainability 2021, 13(21), 11915; https://doi.org/10.3390/su132111915’.
(10) Page 10, Line 337-339: Please specifically add ‘K. senegalensis’.
(11) Minor grammar correction is required.
(12) Page 11, Line 384: Check spelling of ‘Riview’.
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Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Although it is commendable to investigate a new dedicated energy crop, i.e., khaya, for bioenergy production, there are significant lacunae in the methods and discussion section as listed below:
1) Where was the khaya wood harvested from? Please give the precise location (longitude and latitude, if possible) and also summarize the harvesting practices.
2) How much wood was harvested, and how did you select the sample for pelleting process?
3) Did you debark the wood? Also, did you conduct chemical compositional analysis? Lignin and protein are mentioned several times as a source of binding and improving mechanical strength of the pellet. Therefore, it is essential to provide the composition of cellulose, lignin, protein, lipids, etc.
4) What is the pelleting machine's capacity (kg/h)? How much pellets (in g or kg) did you produce per testing condition? If you only made 3 pellets per condition, is this pelleting method even reproducible?
5) Would a sample size of 3 be sufficient to provide representative information about a batch of pellet? Shouldn't you test at least 10 samples per condition?
6) Line 47: How much biomass does Khaya actually yield per unit area? And what is the estimated feedstock supply from this wood source per year (you may make assumptions to come up with this value, but please mention those assumptions)?
7) ANOVA is not the best method to compare means for this kind of experimental set up. I recommend to use a Tukey's test, which will provide the "honest significant difference" between each test group.
8) Please do not try to fit a trend line for such kind of data set. It is unnecessary. I highly recommend to remove the trend lines and trend prediction. Please leave it at determining the level of honest significant difference using a Tukey's test.
9) Significant rewrite is recommended based on the new statistical analyses.
10) English language needs extensive edits. There are several grammatical errors.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript, in its current state, is not suitable for publication in a scientific journal.
1. The abstract should be linked to the conclusions. The abstract should present the most important results of the experiments and not only justify why the manuscript was written. The present information in the abstract should be communicated in the "Introduction" section. It should be corrected.
2. The parameters of the pellet are not given: diameter, average length, moisture content, and specific mass. Provide these parameters to make the manuscript sense.
3. The authors did not explain in the methodology what type of machine (Manufacturer's name, type, technical parameters) they used to make the pellets and how they determined the temperature, among other things shown in Figure 3. Is the temperature they refer to the value of the die temperature during the pelleting process, or is it the temperature of the heated raw material before subjecting it to pelleting? Also, in line 172, there is an error "The maximum 171 value of mechanical durability (99.6 °C)..."
4. I recommend that the authors think about the regression equations. Does the 4th-degree equation make sense? According to the reviewer, it does not make sense and, in addition, it introduces unjustified of results of measurements, the line inflection in the range of 25 - 50 °C and 100-120 °C (Fig. 3, Fig. 4, Fig. 6, Fig. 7). Maximum second-degree equations are completely sufficient in these cases. The measurement results shown in Figure 8 suggest exceptionally well using the first-degree-linear equation to describe them. Fitting an equation by force, solely guided by the need to obtain a coefficient of R2 to the average values of the measurements equal to 1, is scientifically unjustified and may introduce errors.
5. You also need to clarify: what was taken as the values of the whiskers in all graphs? Are they ±standard deviation or ±standard error, or the maximum and minimum values obtained from the measurements?
5 In describing the strength measurements using a press, the authors did not write how many pieces of pellets obtained from the specified pellet-making parameters were taken to the measurements. This is the essential information and allows one to look critically at the results, especially regarding the so-called "saddle trend" that the authors cite in the text, lines 298 to 303.
I also point out to the authors that from a scientific point of view, the conditions of comparability must be met to compare something with each other. The research must involve the same or similar object, and the parameters for performing the research must be similar or the same. Comparing the results described in this manuscript to the results of measurements from the papers {31] and [32], which deal with completely different phenomena, is unjustified and should not occur in this manuscript.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
1) There are several repetitions (of concepts and terms) in the newly revised sentences; please correct. E.g. please remove the line, "Khaya senegalensis wood chips were ground in this experiment to obtain the desired experimental particle size.", because you have already mentioned this step in previous Lines (122-124). Similarly, the concept of the "biomass being pelletized at different pressures and temperatures" has been repeated 3 times. Kindly delete repeated concepts and shorten the methods section.
2) Please delete the line: "It can be seen in several papers that three replicates were used for each characterization of biomass materials [17]–[19]". It was sufficient to answer this reviewer in the response document and there is no need to add such a statement to the main manuscript.
3) Based on the "CEN/TS 15149-2" method and the mesh size of the sieve used to screen the wood powder, could you please provide the average particle size? This parameter is really important to compare your results with future publications.
4) Please delete the following sentences;
"Several researchers worked on pelletizing biomass feedstocks using manual press [20]–[22]. Thus, the current study opted for the manual press as it is more cost-effective to investigate the fundamental factors affecting fuel pellet qualities using a manual press before continuing with bulk production".
"Analysis of variance (ANOVA) is a statistical technique used to compare the means of three or more data groups. It determines whether there is a statistically significant difference between the means of the groups and, if so, identifies which groups differ."
"ANOVA is based on the assumption that the data is usually distributed and that the variances of the groups are equal. It is widely used in research studies to analyze the effects of different factors on a response variable."
Such statements are not required in the main manuscript. You only need to explain this to the reviewer in the response document.
5) Please edit the sentence (Line 188) as follows: "The whiskers in all graphs are standard errors obtained from triplicate measurements."
6) Line 24: Please do not provide more than one or two decimal points (i.e., 13.8% and not 13.8037%) unless it is significant. Same comment for p-value provided in Line 236.
7) Line 229: Please do not use unprofessional terms like "reported by scholars". It is recommended to use passive voice, such as "previous reports, studies, or research".
8) Italicize Khaya senegalensis in Line 402
9) Instead of saying "A bi-response analysis" in line 403, please say, "A univariate analysis..."; because the independent variables were evaluated one at a time.
10) The conclusion must be re-written, where only the parameters selected for future research is highlighted. Right now, when all results are summarized, the final message from the authors is unclear!
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors of the manuscript have taken my comments into account.
I have no further comments.
Author Response
The authors would like to thank you for the constructive comments, effort and precious time put into reviewing this manuscript.
