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The manuscript is much improved and meets the quality standards of the journal.
Thus, it can be accepted for publication.
[# PeerJ Staff Note - this decision was reviewed and approved by Jörg Oehlmann, a PeerJ Section Editor covering this Section #]
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Authors prepared well the revised manuscript according to reviewers' comments, and I have no further comment.
The revised manuscript has been greatly improved from the original version.
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The reviewers provided comments that were not in favor of publication.
-The authors should provide more information connecting the results and dscussion sections.
-The methodology is unclear, and the experimental design does not adequately support the findings.
-A clear explanation of the functional activity and biofiltering performance of the fungi and bacteria should be provided.
**PeerJ Staff Note:** Please ensure that all review, editorial, and staff comments are addressed in a response letter and that any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.
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- Not enough literature references are provided, there are entire paragraphs without references. - Line 61-62, references are missing. - Lines 62-69 do not have a single reference, add your references.
- Raw data is shared, but the labels are not descriptive enough to understand what is what. There are no units specify in the raw data either.
-Some sentences are confusing, too long and hard to read. - Sentence in lines 66-69 is too long and convoluted, please simplify.
There are some basic issues in the introduction:
- Line: 41-43: this seems not properly described, VOCs are transferred to biofilms and finally to the microorganisms? Microorganisms are part of the biofilm. Please rephrase this.
- Enumerate equations. Eq in line 45 is not enumerated.
- Include units in your equations and when you define your variables!!
- Line 51-53, adding the equation that shows the relationship between RE, mass transfer and microbial activity would help better describe this.
- Line 61-62, references are missing.
- Line 58, mention the obvious advantages of FB systems for VOC removal and performance stability.
- Lines 62-69 do not have a single reference, add your references.
- Line 63, fungi increase the accessibility of contaminants and nutrients for bacteria by extending their hyphae, how??
- Line 64, which substances?
- Sentence in lines 66-69 is too long and convoluted, please simplify. Line 66, what chemicals do bacteria secrete that can help fungal growth etc.?
- Include equation that describes how MRs and REs were obtained.
- Lines 73-75. This sentence implies that the authors already knew F&B-BFs would be ‘superior’ to other BFs. I suggest changing the word “explicate” to “the aim of this work was to evaluate… the performance of… and explain the potential mechanisms… etc.”
- Figure 1: misspelling of the word ‘water’.
- Figure 1, legend should include a more detailed description of the system. There is a lot going on in this image.
- Methods are not described with sufficient detail and information to replicate. The authors constantly refer to other papers without providing at least a summary of the method that was used. Referencing a method from another paper is not just enough. Your paper should be stand-alone and if needed, the reader can look for other references for further detail, but the reader should not need to look for over 10 other papers to understand the work done in this manuscript.
Examples:
- Lines 85-95, there is only a description of the biofilters (e.g., the actual bioreactor), but no description of the water bath & bubblers, mixing chamber, flows, depicted in Fig 1. Is cleaned air used in the bubblers? What is the flow in those rotameters? Description of the humidifier is also missing.
- Line 98-99, describe briefly what the inducer-target graded acclimation strategy and gas-liquid phase joint inoculation methos is.
- If activated sludge was used as the inoculum in the B-BF (line 98), wouldn’t you expect the presence of fungi as well? How can you assure that this only contained bacteria? Was the sludge treated in a specific way to ensure only the presence of bacteria?
- What was the inoculum for the F&B-BF?
- Line 100, describe the two steps used.
- Line 103. Provide the recipe for MSM, at least as a supplementary information. The reader should not have to be looking out for other papers to figure out every single step followed by this paper.
- Line 108, why were the pHs of the MSM different for the different treatments? Justify.
- How long were the reactors run for?
- How often were gas samples taken?
- Lines 115-118. I get that you do not want to re-write methods that have already been published, but you can summarize them and then reference the original method if the reader wants further detail. Line 117 talks about pressure drop, when there is no context of where this is coming from. I am familiar with these systems and I understand what this means, but anyone else new to the topic needs context.
- Where are the constant values used in your equations from e.g., 3.38, 3.335, 3.32… explain what they mean.
- Line 128, describe method.
- Line 129, what is a timely manner? Please be specific, when was this measured?
- Line 129, describe the method. When were samples taken?
- Line 130, what is the zeta potential used for?
- Line 136, when were the samples analyzed? When inoculated? At the end of the experimental run? Over time? How were these samples collected? Please be more specific!
Results are sometimes mentioned but the actual numbers are not presented. There is a lack of statistical analysis (at least show standard deviations) to sustain that the differences observed are significant. The results presented do not sustain the conclusions
Examples:
- A statistical analysis to compare the differences in Res between the different treatments should be performed. For instance, Res of T were 90-93% and >95% for B and FB, respectively. These values are quite close, and without seeing any std it is hard to assertively say there is a significant difference.
- Line 144, were these the concentrations in the influent or effluent?? And was this just for B-BF? What about B-&F-BF?
- Line 158-161, refer to Fig. 2.
- Line 169, which strains?
- Line 171, F-BF? Is this a typo? Should this be B&F-BF?
- Lines 173-174, where can we see these results?
- Line 176, higher negative potential of what?
- Lines 178-182, please re-work this paragraph, it is quite confusing.
- Line 188. It was not indicated in the methods section that there would be EBRTs comparison. Add that to your methods section.
- Line 191-192, where can we see these results?
- The word biofilm is used several times but it was never defined.
- Line 223-228, so is there more biomass in the B-BF?
- You also talk about longer growth rates of fungi, that is highly variable depending on the system.
- Figure 6, without std in the graphs, it is really hard to assess differences.
- Line 265, this should be explained as part of your methods!
- Lines 260-261, where are these results?
- So, the B-BF also contained fungi, just in a lower ratio, correct? Thus, I believe it is not fair to call this paper a comparison of B-BF and F&B-BF, given that there was presence of fungi in both systems.
- Lines 201-209, the authors state: The BTEp adsorption by fungal mycelium increased the contact time between…..degrading bacteria were uniformly distributed in biofilms because of “Fungal highways”, and which reduced the distances between the bacteria and their substrates and simultaneously increased the contact frequency between the biocatalysts and their hydrophobic substrates. This is just a mere speculation of the authors. Although possible that a fungal mycelium developed and bacteria might have grown on the fungal hyphae, the authors do not show proof of this. There are no microscopy images or other proof of this. The fact that the authors performed microbial community analysis and found fungi and bacteria together, does not necessarily imply that they developed synergistic interactions or were physically associated. The authors need to rephrase this paragraph, they can say something like ‘ it is probable, or microbes might have associated…” but do not use this as a statement of this actually happening because they do not have proof of this.
Conclusions:
- Conclusion #3: By comparison with the B
Summarizing:
This work is relevant, but the way it is presented is flawed. I want to highlight that the main issue with this manuscript is that the authors claim to be comparing the performance of bacterial-biofilters vs fungal-bacterial-biofilters. But this is not accurate, because both biofilters actually demonstrate the presence of fungi as part of their microbial community. The methods are not properly described. There is no statistical analysis that can sustain the differences among treatments. Conclusions are not sustain given the presence of fungi in both systems.
Abstract:
- Relevant information is missing, e.g., were the biofilters inoculated with model species or environmental samples?
- Unnecessary use of abbreviations, e.g., Res, MRs, which are not used at all in the abstract.
- Removal efficiencies by F&B-BF were higher compared to B-BF, by how much?
The manuscript entitled "A comparison of the performance of bacterial biofilters and fungal-bacterial biofilters for BTEp-X removal” has been reviewed. It is a topic of interest to the researchers in the related areas and the structure of this manuscript is well organized, I would like to recommend a minor revision before the acceptance of this work for publication. The main concerns about this manuscript can be found below:
Introduction
Lines 45 and 47: The formulas are presented in the correct order.
Lines 60 and 65: Please include references.
Lines 65 and 69: Improve readability.
Materials and methods
Line 114: If you decide to use an abbreviation for gas chromatography (GC) make sure you do it throughout the text.
Line 123-124: Are the concentrations of airborne CO2 at the inlet negligible?
How to control the excessive accumulation of biomass within the B−BF and F&B−BF?
Results and discussion
Line 138-139: overall: if you decide to use an abbreviation for each VOC (B, T, E, p−X) make sure you do it throughout the text.
Line 139: Why p-xylene was chosen as the model VOC instead of o-xylene or m-xylene?
Line 134 and Line 259: RT‒qPCR or qRT‒PCR? Keep uniformity throughout the text.
Line 176-178: Check the reference.
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Excellent Review