Research Progress and Applications of Microbial Deodorization Technology
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn the manuscript Research Progress and Applications of Microbial Deodorization Technology the authors address a topic fairly less studied and disseminated in the scientific literature, that of unpleasant odors associated with natural or anthropogenic processes, despite their pronounced impact on the human and environmental health. Addressing this interesting topic is useful both from the practical perspective of improving microbial degradation processes of organic residues and wastewaters, and from the academic, theoretical perspective of understanding and deepening some complex mechanisms of microbial degradation.
Overall, the manuscript is structured into relevant chapters and subchapters; it is drafted with high responsibility and skill.
The introduction is quite concise but able to provide important information on the impact of odorous gases from various perspectives. The usual physicochemical techniques that are currently used are briefly listed, as well as the less in-depth microbial ones, which can bring undeniable economic, social and environmental benefits. The authors emphasized the novelty of this study by highlighting the shortcomings of other published documents, mainly the need for a complex understanding of microbial processes in the context of some practical applications.
The chapters that make up the main text have undeniable scientific and practical importance; I believe they are able to support developers of such microbial deodorization systems in reducing the negative impact associated with various applications for processing or treating organic materials. I note positively that the authors presented relevant information in a concise manner, with tabulated data that can be easily assimilated and compared. These data are supported by clear, eloquent graphic images that graphically depict the complex metabolic mechanisms of biodegradation in a simplified form that is easy to understand and transferred from theory to practical use.
Mechanisms of biochemical processes and the factors influencing these microbial processes are discussed with reference to current scientific bibliography.
Conclusions of this study follow closely the most important issues discussed in the text; research directions requiring further investigation have also been clearly identified and highlighted.
Author Response
Reviewer #2
Comments: In the manuscript Research Progress and Applications of Microbial Deodorization Technology the authors address a topic fairly less studied and disseminated in the scientific literature, that of unpleasant odors associated with natural or anthropogenic processes, despite their pronounced impact on the human and environmental health. Addressing this interesting topic is useful both from the practical perspective of improving microbial degradation processes of organic residues and wastewaters, and from the academic, theoretical perspective of understanding and deepening some complex mechanisms of microbial degradation.
Overall, the manuscript is structured into relevant chapters and subchapters; it is drafted with high responsibility and skill.
The introduction is quite concise but able to provide important information on the impact of odorous gases from various perspectives. The usual physicochemical techniques that are currently used are briefly listed, as well as the less in-depth microbial ones, which can bring undeniable economic, social and environmental benefits. The authors emphasized the novelty of this study by highlighting the shortcomings of other published documents, mainly the need for a complex understanding of microbial processes in the context of some practical applications.
The chapters that make up the main text have undeniable scientific and practical importance; I believe they are able to support developers of such microbial deodorization systems in reducing the negative impact associated with various applications for processing or treating organic materials. I note positively that the authors presented relevant information in a concise manner, with tabulated data that can be easily assimilated and compared. These data are supported by clear, eloquent graphic images that graphically depict the complex metabolic mechanisms of biodegradation in a simplified form that is easy to understand and transferred from theory to practical use.
Mechanisms of biochemical processes and the factors influencing these microbial processes are discussed with reference to current scientific bibliography.
Conclusions of this study follow closely the most important issues discussed in the text; research directions requiring further investigation have also been clearly identified and highlighted.
Response: We sincerely appreciate your careful review and valuable time spent on our manuscript. Since no specific comments were raised, we hope the revised version can meet your academic requirements.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors=36, authors should provide some idea where these odorous gases are produced and need the solution , like in biogas scrubber?
=76, authors should indicate the source of this data like NH3 from livestock urine and H2S from anaerobic digestion?
=98 provides more limited coverage .....please revise this sentence to be clear
=163,The generated S⁰ ......is it in solid or soluble form?
=188,specialized VOC-degrading microorganisms .....please give examples
=213 broad-spectrum oxygenases .....what does it mean, please add more details. is it like no-specific substrate?
=244 Typically, a moisture content of 50-70% is considered optimal for biodegradation processes. ....please explain more. in which substrate of these reactions?
=277,prevent excessive accumulation of elemental sulfur 277 on biofilm surfaces, thereby avoiding packing material clogging. .....please add reference to support the relationship beterrn sulfur and material clogging
=357, authors should add brief details about the proportion or % abundance to all microbes or loading?
Author Response
Reviewer #3
Comments 1: =36, authors should provide some idea where these odorous gases are produced and need the solution , like in biogas scrubber?
Response: We appreciate your suggestion. Typical production scenarios of malodorous gases have been supplemented in the corresponding text as requested. The revised contents are as follows.
Odorous gases are generated from daily human activities as well as agricultural and industrial production processes, including livestock and poultry farming (e.g., animal housing and manure storage facilities), organic solid waste treatment (e.g., municipal solid waste composting plants and sanitary landfills), and wastewater and sludge treatment (e.g., anaerobic digesters, biogas upgrading scrubbers, and sludge dewatering and composting units), all of which represent key scenarios requiring effective odor control solutions. (Page 1, Lines 35-41)
Comments 2: =76, authors should indicate the source of this data like NH3 from livestock urine and H2S from anaerobic digestion?
Response: Thank you for pointing out this deficiency. Clear sources of relevant data (e.g., NH₃ from livestock urine and H₂S mainly generated during anaerobic digestion) have been marked in the manuscript. The revised contents are as follows.
NH3 is predominantly derived from the enzymatic hydrolysis of urea in animal urine by urease-producing microorganisms, as well as from the microbial decomposition of nitrogenous organic matter in feces[8]. H2S is mainly generated through the anaerobic microbial reduction of sulfate and the degradation of sulfur-containing amino acids (e.g., cysteine and methionine) under anaerobic conditions in manure pits and slurry storage facilities[9]. (Page 3, Lines 92-97)
Comments 3: =98 provides more limited coverage .....please revise this sentence to be clear
Response: We thank you for your careful reading. The confusing sentence has been rewritten to clarify that current Chinese standards cover limited types of pollutants and lack targeted specifications for different industrial sectors. The revised contents are as follows.
The comparison of threshold values for major indicators indicates that Chinese standards set relatively lenient limits, while gaps remain in pollutant coverage and differentiated regulatory requirements for different industries (Table 2). (Page 3, Lines 119-121)
Comments 4: =163, The generated S0 ......is it in solid or soluble form?
Response: We appreciate your question. The text has been revised to clarify that the generated elemental sulfur (S⁰) exists in solid form. The revised contents are as follows.
The oxidation of H2S is initiated by membrane-bound Sqr, which catalyzes the two-electron oxidation of H2S and drives the deposition of the resulting sulfane sulfur as solid-phase elemental sulfur (S0). (Page 6, Lines 185-187)
Comments 5: =188, specialized VOC-degrading microorganisms .....please give examples.
Response: Thanks for your suggestion. Specific strains of specialized VOC-degrading microorganisms have been supplemented as examples in the revised text. The revised contents are as follows.
Accordingly, the construction of microbial consortia comprising specialized VOC-degrading microorganisms capable of C-S bond cleavage and highly efficient sulfur-oxidizing bacteria responsible for H2S removal represents an effective strategy for the complete and stable elimination of sulfur-containing VOCs, such as Acidithiobacillus thiooxidans and Thiobacillus thioparus[42]. (Page 6, Lines 218-222)
Comments 6: =213 .....what does it mean, please add more details. is it like no-specific substrate?
We appreciate your inquiry. We have rephrased the relevant description to clarify that the enzyme is an oxygenase with a broad substrate spectrum capable of catalyzing structurally diverse substrates, rather than an enzyme with absolutely no substrate specificity. The revised contents are as follows.
For example, the toluene dioxygenase (TDO) encoded by the todC1C2BA operon in Pseudomonas putida F1 can oxidize not only toluene but also benzene, ethylbenzene, naphthalene, and several chlorinated aromatic compounds, making it a representative broad-spectrum oxygenase applicable to mixed aromatic VOC treatment scenarios[47]. (Page 7, Lines 246-250)
Comments 7: =244 Typically, a moisture content of 50-70% is considered optimal for biodegradation processes. ....please explain more. in which substrate of these reactions?
Response: Thank you for this valuable question. We have revised the text to clarify that the optimal moisture content range of 50-70% applies specifically to composting systems. For liquid-phase bioreactors such as biofilters and bioscrubbers, moisture content is not a dominant influencing factor. The revised contents are as follows.
In solid-phase composting systems treating organic substrates such as animal manure, municipal solid waste, and sewage sludge, a moisture content of 50-70% is generally considered optimal for microbial degradation activity, as it simultaneously satisfies the requirements for substrate solubilization, microbial mobility, and adequate oxygen diffusion through the porous matrix[61]. (Page 8, Lines 279-283)
Comments 8: =277, prevent excessive accumulation of elemental sulfur 277 on biofilm surfaces, thereby avoiding packing material clogging. .....please add reference to support the relationship between sulfur and material clogging.
Response: Thanks for your reminder. Corresponding literatures have been supplemented to provide evidence for the correlation between elemental sulfur accumulation and packing material clogging. The revised contents are as follows.
Screening strains with high expression of key genes such as sqr, dsrA, and soxB can effectively prevent excessive accumulation of elemental sulfur on biofilm surfaces, thereby avoiding packing material clogging[76]. (Page 10, Lines 318-320)
Reference: [76] Sutarut, P.; Cheirsilp, B.; Boonsawang, P. Biodesulfurization of Consortia Immobilized on Oil Palm Frond Biochar in Biotrickling Filters under Anoxic Conditions. Fermentation 2023, 9, 664. (Page 22, Lines 804-805)
Comments 9: =357, authors should add brief details about the proportion or % abundance to all microbes or loading?
Response: We appreciate your comment. The detailed microbial composition and relative abundance of these commercial bacterial agents are not publicly available due to commercial confidentiality. The relevant quantitative data are sourced from official websites of corresponding manufacturers, with citations marked in tables. Therefore, further detailed descriptions are not available at present.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe review addresses an interesting topic, presenting odor sources, removal mechanisms, reactor technologies, and the presence of microorganisms.
The authors should include a section on the methodology. The aim of the report should be clearly stated. Table 1 has no references and no quantitative information.
At line 42, the authors report that the VOCs are involved in the ozone layer depletion. What about the CFCs? Please confirm that the reference includes this statement.
Line 48, Reference.
Line 110, regarding the removal of ammonium, the comammox and anammox are completely disregarded.
The authors should carefully check whether the references cited in the text support what they are stating. One example is reference 26 (line 122) that has a title ‘’Wastewater Treatment Plants as a Source of Malodorous Substances Hazardous to Health’’. Then lines 122-128 have no reference. Again, the authors refer to Paracoccus pantotrophus (line 168), and the reference is on Acidithiobacillus caldus. The authors report 100% toluene removal (Table 7), but this information comes from a review article, and they also need to verify whether it is true.
Lines 134-143, the nitrogen transformations are repeated.
Lines 293-294 and 436, " Elimination capacity " and " Removal loading rate “, please consider rephrasing. Please use consistent phrasing.
Line 204: The authors refer to ‘’Alkane hydroxylase’’, and Figure 3 presents it as an extracellular enzyme, or as something that is unclear. Moreover, I am not sure that the smiling face in Figure 3 is scientific and necessary.
Figure 4. What is the meaning of ‘’Bump’’?
The manuscript includes acknowledgments but no author contributions section, funding information, data availability statement, etc.
Author Response
Reviewer #1
Comments 1: The authors should include a section on the methodology. The aim of the report should be clearly stated. Table 1 has no references and no quantitative information.
Response: We appreciate your constructive suggestions. Corresponding references have been supplemented to support Table 1. Limited quantitative data are presented in this table owing to insufficient quantitative records in existing literatures, and the concentrations of various odor components also fluctuate remarkably under different practical operating conditions. The revised contents are as follows.
Methods
The literatures reviewed in this study were retrieved through a systematic search of the Web of Science and Scopus databases, using Boolean search strings combining core terminology relevant to microbial deodorization, such as “bio* AND odor* AND remov*”, “biofilter* AND hydrogen sulfide”, and “ammonia AND microbial AND treatment”. The search results were subsequently refined by applying inclusion criteria limited to peer-reviewed original research articles and reviews published in English, with studies unrelated to biological odor control or lacking microbial characterization data excluded. Following title and abstract screening, the retained articles were subject to full-text review, and the ultimately incorporated literatures were analyzed and categorized according to the following parameters: target odorants, bioreactor configuration, dominant functional microorganisms, key metabolic enzymes, removal efficiency, and operational conditions. (Page 2, Lines 72-83)
Table 1. Major components and emission pathways of odorous gases from different sources[23](Page 3, Lines 108)
Comments 2: At line 42, the authors report that the VOCs are involved in the ozone layer depletion. What about the CFCs? Please confirm that the reference includes this statement.
Response: Thank you for the careful check. The cited reference only states that VOCs contribute to global warming without any discussion on ozone layer depletion. We have revised the problematic statement in the manuscript accordingly. The revised contents are as follows.
The emission of NH3 results in nitrogen loss[2], atmospheric H2S contributes to the formation of photochemical smog and acid rain[3,4], and VOCs are implicated in global warming and a range of other environmental problems[5]. (Page 2, Lines 46-48)
Comments 3: Line 48, Reference.
Response: We appreciate your reminder. Relevant references have been added at Line 48 to back up the statements in the text. The revised contents are as follows.
Microbial deodorization, which emerged in the 1950s, is an innovative technology in which odorous compounds are degraded through the metabolic activities of microorganisms[6]. (Page 2, Lines 53-55)
Comments 4: Line 110, regarding the removal of ammonium, the comammox and anammox are completely disregarded.
Response: This is a critical point you raised. We have supplemented the descriptions of comammox and anammox pathways together with corresponding references in the revised manuscript. The revised contents are as follows.
Beyond this classical framework, two additional autotrophic pathways have been identified. Anaerobic ammonium oxidation (anammox), carried out by Planctomycetes such as Candidatus Brocadia and Candidatus Kuenenia, directly converts NH4+ and NO2- to N2 under strictly anaerobic conditions without any carbon source[31]. Complete ammonia oxidation (comammox), first described in certain Nitrospira strains, enables a single organism to independently accomplish the full NH4+-to-NO3- conversion previously assumed to require the coordinated activities of both AOB and NOB[32]. Although both pathways have been detected in biofilters and compost matrices, their contributions to NH3 attenuation in odor control scenarios remain limited compared with conventional nitrification-denitrification, and their ecological roles in deodorization systems warrant further investigations. (Page 4, Lines 147-157)
Comments 5: The authors should carefully check whether the references cited in the text support what they are stating. One example is reference 26 (line 122) that has a title “Wastewater Treatment Plants as a Source of Malodorous Substances Hazardous to Health”. Then lines 122-128 have no reference. Again, the authors refer to Paracoccus pantotrophus (line 168), and the reference is on Acidithiobacillus caldus. The authors report 100% toluene removal (Table 7), but this information comes from a review article, and they also need to verify whether it is true.
Response: Thanks for your thorough review. We have carefully examined all citations throughout the manuscript and revised inconsistent contents to guarantee that each statement is well supported by cited literature. References have been added for paragraphs without citations. In addition, we have cross-verified all data to ensure authenticity and reliability. The revised contents are as follows.
Hydroxylamine is subsequently oxidized to nitrite (NO2⁻) by hydroxylamine oxidoreductase (HAO). Nitrite-oxidizing bacteria (NOB), such as Nitrobacter, further oxidize NO2⁻ to nitrate (NO3⁻) via periplasmic nitrite oxidoreductase (NXR)[30]. (Page 4, Lines 144)
Under oxygen-limited conditions, denitrifying bacteria (DNB) sequentially reduce nitrate to nitrogen gas (N2) through the catalytic actions of nitrate reductase (Nar), nitrite reductase (Nir), nitric oxide reductase (Nor), and nitrous oxide reductase (Nos)[30]. (Page 4, Lines 147-151)
Reference:
[30] Roothans, N.; Pabst, M.; van Diemen, M.; Herrera Mexicano, C.; Zandvoort, M.; Abeel, T.; van Loosdrecht, M.C.; Laureni, M. Long-term multi-meta-omics resolves the ecophysiological controls of seasonal N2O emissions during wastewater treatment. Nature Water 2025, 3, 590-604. (Page 20, Lines 699)
When H2S concentrations are relatively low or complete oxidation is required, H2S can be directly oxidized to sulfate (SO₄²⁻) by the sulfur oxidation (Sox) system, such as the SoxXYZAB complex in Arcobacter butzleri, without the accumulation of detectable intermediates[40]. (Page 6, Lines 197-200)
Comments 6: Lines 134-143, the nitrogen transformations are repeated.
Response: We thank you for pointing out the redundant contents. The repetitive descriptions of nitrogen transformation have been removed in revision. The revised contents are as follows.
The nitrogen metabolic pathway of HN-AD bacteria has not yet been fully elucidated, and two putative pathways have been proposed[34]: (i) NH4+ → NH2OH → NO2− → NO → N2O → N2, in which transient accumulation of NO2− and NO3− has been observed before their subsequent reduction; (ii) NH4+ → NH2OH → NO → N2O → N2, in which the hydroxylamine produced from NH4+-N oxidation is directly converted into N2 through the denitrification pathway[35]. (Page 5, Lines 165-171)
Comments 7: Lines 293-294 and 436, “Elimination capacity” and “Removal loading rate”, please consider rephrasing. Please use consistent phrasing.
Response: We appreciate your suggestion on terminology normalization. We have unified the related term as “Removal loading rate” across the full manuscript. The revised contents are as follows.
Studies have shown that, for hydrophobic gases such as toluene and xylene, fungal biofilters typically achieve 20-40% higher removal loading rate than bacterial systems. (Page 10, Lines 334-336)
Comments 8: Line 204: The authors refer to “Alkane hydroxylase”, and Figure 3 presents it as an extracellular enzyme, or as something that is unclear. Moreover, I am not sure that the smiling face in Figure 3 is scientific and necessary.
Response: Thank you for your comments on Figure 3. We have revised Figure 3 to eliminate ambiguous descriptions of alkane hydroxylase. The smiley face icon has been replaced with standard schematic symbols to comply with formal academic drawing norms. The revised contents are as follows.
Figure 3. Removal mechanism of sulfur-free VOCs. (Page 8, Lines 254-255)
Comments 9: Figure 4. What is the meaning of “Bump”?
Response: We apologize for the typographical error in Figure 4. The label "Bump" was a writing mistake, and the correct term is “Pump”, which refers to the circulation pump inside the reactor. The figure has been corrected accordingly. The revised contents are as follows.
Figure 4. Schematic diagram of deodorization bioreactor. (Page 16, Lines 515-516)
Comments 10: The manuscript includes acknowledgments but no author contributions section, funding information, data availability statement, etc.
Response: Thanks for your reminder on standard manuscript sections. We have supplemented the Author Contributions statement, funding acknowledgements, and Data Availability Statement in the revised manuscript. The revised contents are as follows.
Author Contributions:
Yunhao Liu: Conceptualization, Literature search, Data curation, Writing-Original Draft Preparation, Writing-Review and Editing. Wenbo Zhang: Literature Search, Data Curation, Writing-Review and Editing. Mengqi Shen: Literature Search and Data Curation. Xu Xu: Literature Search and Data Curation. Jing Geng: Literature Search and Data Curation. Weiliang Dong: Conceptualization, Resources, Supervision, Project Administration, Funding Acquisition, Writing-Review and Editing; Xiayuan Wu: Conceptualization, Methodology, Resources, Supervision, Project Administration, Funding Acquisition, Writing-Review and Editing.
Acknowledgments:
This work was financially supported by the National Key Research and Development Program of China (2021YFA0910400), Jiangsu Basic Research Center for Synthetic Biology (BK20233003), the Natural Science Foundation of Jiangsu Province of China for Excellent Young Scholars (BK20211591), the National Natural Science Foundation of China (22478184), the Jiangsu Synergetic Innovation Center for Advanced Bio-Manufacture (XTD2209), and the Provincial Students’ Platform for Innovation and Entrepreneurship Training Program (X2026102910811, X2026102911408).
Conflicts of Interest:
The authors declare no conflicts of interest. (Page 18, Lines 605-621)
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript could be accepted for publication, with the Editor's agreement.
