Enhanced Oxygen Mass Transfer in Mixing Bioreactor Using Silica Microparticles
, Ivus Lorenzo Oliveira Matos 2, Filipe Moreira Mascarenhas Cordeiro 3, Ana Cristina Morais da Silva 3, Eliane Bezerra Cavalcanti 2,4 and Álvaro Silva Lima 3,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsComments
This manuscript used different silica microparticles (silica sol-gel, commercial sand, and beach sand treated by acid-base abrasion) to enhance the kLa and consequently in-crease the system's oxygenation. The experiment is basically reasonable, and meets the requirements of Fermentation.
In addition, there are some points which the authors should address as follows:
1. The particle size distribution for pre-treatment sand beach was missed in Figure 2.
2. In XRD analysis, obvious difference from silica sol-gel was presented, however, the discussion and explanation were missing. Why silica sol-gel showed the totally different crystal structure with the same compound, SiO2.
3. The low resolution of FT-IR in present form could not provide any useful information on functional groups. Please retest and discuss accordingly.
Comments on the Quality of English LanguageGood
Author Response
This manuscript used different silica microparticles (silica sol-gel, commercial sand, and beach sand treated by acid-base abrasion) to enhance the kLa and consequently in-crease the system's oxygenation. The experiment is basically reasonable, and meets the requirements of Fermentation.
In addition, there are some points which the authors should address as follows:
Comment 1. The particle size distribution for pre-treatment sand beach was missed in Figure 2.
Answer: The particle size distribution was performed only for those silica microparticles that were used in the kLa determination experiments (silica microparticles post-treatment). We do not believe that the acid and base treatment would interfere with the particle size distribution, since the purpose would be to eliminate only the organic material. Subsequently, other analyses were carried out for comparison purposes.
Comment 2. In XRD analysis, obvious difference from silica sol-gel was presented, however, the discussion and explanation were missing. Why silica sol-gel showed the totally different crystal structure with the same compound, SiO2.
Answer: The authors are grateful for the suggestion, and added a justification for the difference, despite already mentioning in the manuscript that it occurs.
“According to Yu et al. [32] silica sol-gel presents amorphous characteristics, and only crystalline. The sol-gel silica presented here was not calcined, as the sands have suffered pressure and temperature changes over thousands of years..”
Comment 3. The low resolution of FT-IR in present form could not provide any useful information on functional groups. Please retest and discuss accordingly.
Answer: The FT-IR spectrum presents characteristic bands for silica particles in accordance with the literature and discussed in the manuscript.
“All peaks appear in the same position independent of the kind of silica microparticle. The spectra do not present the bands for the lowest frequency model (approximately 460 cm-1), assigned to transverse optical (TO1) rocking motions, perpendicular to the Si-O-Si plane, of the oxygen bridging two adjacent Si atoms. The weak peaks of 793 cm-1 are due to the asymmetric stretching vibration of the Si-OH (transverse optical - TO2 model). The peaks between 1087-1091 cm-1 are related to the transverse optical – TO3 model, which involves motion back and forth of the oxygen atom along a line parallel to the Si-Si axis. The motion results in the opposite distortion of two neighboring Si–O bonds and is indicated as an asymmetric stretching vibration of Si-O [26]. According to Beganskiene et al. [27], peaks between 800 and 1200 cm-1 corresponded to the superimposition of several SiO2 peaks, Si-OH bonding, and eventual peaks due to residual organic groups. The peaks at 2300 cm-1 correspond to the chemical bonds with the hydrogen SiHx surface [28]. Finally, the absorption band around 3100-3600 cm-1 represents the overlapping of the O-H stretching bands of hydrogen-bonded water molecules (H-O-H...H) and SiO-H stretching of surface silanols hydrogen-bonded to molecular water (SiO-H...H2O) [29].”
[26] Innocenzi, P. Infrared spectroscopy of sol-gel derived silica-based films: a spectra-microstructure overview. J. Non-Cryst. Solids., 2003, 316, 309-319. https://doi.org/10.1016/S0022-3093(02)01637-X.
[27] Beganskienė, A.; Sirutkaitis, V.; Kurtinaitienė, M.; Juškėnas, R.; Kareiva, A. FTIR, TEM and NMR investigations of Stöber silica nanoparticles. Mater. Sci., 2004, 10, 287-290.
[28] Vásquez-A., M.A.; Rodríguez, G.A.; García-Salgado, G.; Romero-Paredes, G.; Peña-Sierra, R. FTIR and photoluminescence studies of porous silicon layers oxidized in controlled water vapor conditions. Rev. Mex. Fis., 2007, 53, 431-435.
[29] Al-Oweini, R.; El-Rassy, H. Synthesis and characterization by FTIR spectroscopy of silica aerogels prepared using several Si(OR)4 and R’’Si(OR’)3 precursors. J. Mol. Struct., 2009, 919, 140–145. https://doi.org/10.1016/j.molstruc.2008.08.025
We understand that the reviewer could expect a higher resolution, but other published works present bands like those presented. This result is the result of the use of the FT-IR equipment we have. Unfortunately, we cannot redo it as we do not have these samples.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis work aimed to improve the oxygen transfer mass coefficient (kLa) in mixing reactors by adding silica based materials. It is properly designed and illustrated. It is worth to be published.
However, the figures quality shall be improved. many of them look ugly, such as 2,4,7,8,9,10. In this era of the pursuit of scientific beauty, such pictures are a joke.
Next, its vital problem is that characterizaiton of silicas can be described as "Scratch the boot to stop the itching of the foot". Mass transfer coefficient Kla is related to bubbles size etc, as authors also known. While the characterization are all about the Silicas, and we cannot connect the silica properties to the kla directly. It leads to the discussion is very superficial and limits its value.
Figure 12 has a non-english word.
Author Response
This work aimed to improve the oxygen transfer mass coefficient (kLa) in mixing reactors by adding silica based materials. It is properly designed and illustrated. It is worth to be published.
Comment 1. However, the figures quality shall be improved. many of them look ugly, such as 2,4,7,8,9,10. In this era of the pursuit of scientific beauty, such pictures are a joke.
Answer: Initially, we authors were unable to understand the poor quality of the Figures cited, since in our docx manuscript they are well placed and with good resolution. Still perplexed, we went to check the PDF conversion carried out automatically in the journal's system, and noticed that traces appeared that were beyond our control. We understand that upon publication, the magazine's editors will make the necessary adjustments. We undertake to send the figures separately to avoid any problems.
Comment 2. Next, its vital problem is that characterizaiton of silicas can be described as "Scratch the boot to stop the itching of the foot". Mass transfer coefficient Kla is related to bubbles size etc, as authors also known. While the characterization are all about the Silicas, and we cannot connect the silica properties to the kla directly. It leads to the discussion is very superficial and limits its value.
Answer: As stated by the reviewer, the authors are well aware that the size of the bubbles is one of the factors that impact the mass transfer coefficient. Initially we believed that the ricochet of microparticles could shear the bubbles, increasing the surface area, and that there would be a limit to their use so as not to also cause shearing of the biomass. Therefore, we use low agitation conditions. We characterized the silicas so that we could infer their properties and influence on kLa. We conclude that the use of particles improves the kLa in a systemic way regardless of the type of silica microparticles used, demonstrating that we do not need to synthesize silica particles and we can use beach sand with a simple treatment, thus minimizing costs. Although the characteristics of silica do not answer all questions, this knowledge is important in our view. We discuss, with the utmost care.
Comment 3. Figure 12 has a non-english word.
Answer: We apologize to the reviewer for the oversight. We fix the error.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors presented work on improving oxygen mass transfer in a bioreactor for fermentation process. Improving oxygen mass transfer can have significant impact, especially for aerobic fermentation process. Although using silica particles is acceptable for most biological processes, the authors should provide further insights on the feasibility of using concentrations at 1-2 g/L. My concern is whether such high concentrations will cause significant shear stress on the biological media/organisms.
I have also noticed several typos in the manuscript, e.g. XDR instead of XRD in the abstract. Image quality and presentation should be improved. Some of the figures still have borders/frame around them from poor cropping (perhaps).
Although not part of the scope, the work will improve significantly with a demonstration experiment for aerobic fermentation to show the feasibility of the method.
Comments on the Quality of English LanguageThe authors should do further proofreading on the manuscript.
Author Response
Comment 1. The authors presented work on improving oxygen mass transfer in a bioreactor for fermentation process. Improving oxygen mass transfer can have significant impact, especially for aerobic fermentation process. Although using silica particles is acceptable for most biological processes, the authors should provide further insights on the feasibility of using concentrations at 1-2 g/L. My concern is whether such high concentrations will cause significant shear stress on the biological media/organisms.
Answer: The reviewer is correct; the use of silica particles is common in biological media. To avoid shearing of the microbial biomass, we applied low agitation values. This premise was incorporated into the explanation of the limited use of agitation in the process.
“Moreover, limiting agitation is important to prevent shearing of the biomass and thus enable the addition of silica microparticles.”
Coment 2. I have also noticed several typos in the manuscript, e.g. XDR instead of XRD in the abstract.
Answer: The authors revised the entire manuscript.
Comment 3. Image quality and presentation should be improved. Some of the figures still have borders/frame around them from poor cropping (perhaps).
Answer: Initially, we authors were unable to understand the poor quality of the Figures cited, since in our docx manuscript they are well placed and with good resolution. Still perplexed, we went to check the PDF conversion carried out automatically in the journal's system, and noticed that traces appeared that were beyond our control. We understand that upon publication, the magazine's editors will make the necessary adjustments. We undertake to send the figures separately to avoid any problems.
Comment 4. Although not part of the scope, the work will improve significantly with a demonstration experiment for aerobic fermentation to show the feasibility of the method.
Answer: The authors understand the question, but we understand the importance of studies with different approaches to improve kLa in fermenters
Reviewer 4 Report
Comments and Suggestions for Authors
In this paper, the authors studied the influence of the operating conditions system (agitation speed, aeration rate, particle size and particle concentration) to improve the oxygen transfer mass coefficient (kLa) in a mixing bioreactor using silica microparticles. This work is well structured, the results are well interpreted.
The scientific data presented are supported by references from recent years. This scientific paper is consistent with the journal's theme.
The authors should address the following issues:
- Some details regarding the influence of the studied parameters on fermentative processes using filamentous fungi would have been useful.
- Page 4 - Point 2.3 - please check that the operating conditions of the system are correct (aeration rate and particle concentration)
- Page 10 – please check if reference 35 is missing
- Page 12 - the description of the figure 12 should be in English
After a major revision, I recommend publishing the article.
Comments on the Quality of English LanguageThe English language is good. Minor changes are required.
Author Response
Comment 1. In this paper, the authors studied the influence of the operating conditions system (agitation speed, aeration rate, particle size and particle concentration) to improve the oxygen transfer mass coefficient (kLa) in a mixing bioreactor using silica microparticles. This work is well structured, the results are well interpreted. The scientific data presented are supported by references from recent years. This scientific paper is consistent with the journal's theme.
Answer: The authors thank you for your comments
The authors should address the following issues:
Comment 2. Some details regarding the influence of the studied parameters on fermentative processes using filamentous fungi would have been useful.
Answer: This information was added in the introduction and was already in the results, to justify the limitation of the stirring speed.
“… However, using solid particles in the fermenter can lead to hydrodynamic shearing of the biomass, impacting the morphology and viability of bacterial biomass [22] and even filamentous fungi more susceptible to shearing [23]. In this sense, the use of particles can be administered by limiting the aeration and agitation conditions of the medium..”
“…Focusing on operational conditions, several authors report ranges of agitation for the fermentation process when bacteria [47,48] and yeast [49,50] are used or when filamentous fungi are used [51,52]. According to Cui et al. [23], the size and structure of fungal pellets (smooth or fluffy) are influenced by agitation, which can cause cell autolysis. Therefore, this work studied the effect of low agitation rates (50 and 200 rpm), intending to cover different microbial morphologies..”
Comment 3. Page 4 - Point 2.3 - please check that the operating conditions of the system are correct (aeration rate and particle concentration)
Answer: We correct the information
“The influence of the particles in the coefficient of volumetric oxygen transfer was studied by varying the operating conditions of the system, such as agitation speed (50 - 200 rpm), aeration rate (0.5 - 6.0 L min-1, corresponding to 0.17 - 2.0 vvm, respectively), particle size (approximate size: 10, 75, 150 and 350 µm), and the concentration of particles (0.05 to 5.0%, mgL-1)."
Comment 4. Page 10 – please check if reference 35 is missing
Answer: We apologize to the reviewer for the error. We insert the reference 35, which change to 43
“The values for silica obtained by the sol-gel technique are noteworthy and agree with published data for similar systems [39,43, 44].”
Comment 5. Page 12 - the description of the figure 12 should be in English.
Answer: We apologize to the reviewer for the oversight. We fix the error.
Reviewer 5 Report
Comments and Suggestions for AuthorsThe authors' original research article evaluated oxygen mass transfer in bioreactor cultures under varied agitation and aeration. However, the main aim of the paper was to evaluate the applicability of silica microparticles obtained through the sol-gel technique, commercial sand, and pre-treated beach sand. Firstly, the silicas were compared and characterized using various techniques such as SEM, XRD, and FTIR. These results are extremely valuable and interesting, in my opinion. Then, the authors confirmed the influence of silica particle size and concentration on oxygen mass transfer.
The major flaw of the manuscript is the lack of statistical analysis. The authors should primarily analyze the results presented in Figures 11 and 12.
The discussion of the results may be improved.
Moreover, the introduction should be deepened and broadened, and the authors should rephrase the aim of the work to emphasize its novelty.
Figure 12 - "Concentration" instead of "Concentração"
Author Response
Comment 1. The authors' original research article evaluated oxygen mass transfer in bioreactor cultures under varied agitation and aeration. However, the main aim of the paper was to evaluate the applicability of silica microparticles obtained through the sol-gel technique, commercial sand, and pre-treated beach sand. Firstly, the silicas were compared and characterized using various techniques such as SEM, XRD, and FTIR. These results are extremely valuable and interesting, in my opinion. Then, the authors confirmed the influence of silica particle size and concentration on oxygen mass transfer.
Answer: The authors thank you for your comments
Comment 2. The major flaw of the manuscript is the lack of statistical analysis. The authors should primarily analyze the results presented in Figures 11 and 12.
Answer: Statistical analysis was added to the methodology.
“2.4. Statistical Analysis
The experimental data for studies on the influence of agitation speed, aeration rate and the size and concentration of silica microparticles were compared by a Tukey test and their significance was established by ANOVA. Differences of p ≥ 0.05 were considered statistically significant.”
Statistical analysis for the experimental data referring to Figures 9, 10, 11 and 12 were added to the manuscript.
Comment 3. The discussion of the results may be improved.
Answer: Some discussions or comparisons with literature data were added to the manuscript, as well as statistical analysis for the influence of silica particles
Comment 4. Moreover, the introduction should be deepened and broadened, and the authors should rephrase the aim of the work to emphasize its novelty.
Answer: The authors increase the introduction in sense to deep and broad the information about the influence of particles to increase the KLa
We rephased the aim of the word, emphasizing its novelty.
“This work aimed to expand the study the effect of inserting silica microparticles (sol-gel silica, commercial sand, and beach sand treated by acid-base abrasion), using low agitation speed to avoid the shear of biomass, in a bioreactor on improving kLa, evaluating the possibility of using natural microparticles in the aeration process, which has not yet been observed in the literature.”
Comment 5. Figure 12 - "Concentration" instead of "Concentração"
Answer: We apologize to the reviewer for the oversight. We fix the error.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors correct something.
Author Response
Comment 1: The authors correct something.
Answer: The three questions were answered, and since all questions asked to the magazine for the reviewer about the article are yes, we understand that we have resolved the problems.
Reviewer 4 Report
Comments and Suggestions for AuthorsDear Editors,
The authors have addressed all the comments in revised version. I think it can be accepted for publication now.
Thank you for the opportunity to review this manuscript.
Author Response
Comment 1 -The authors have addressed all the comments in revised version. I think it can be accepted for publication now.
Answer: The authors thank the reviewer for the opportunity to improve the work.
Reviewer 5 Report
Comments and Suggestions for AuthorsThe authors addressed my comments and suggestions but the results of the statistical analysis should be presented on figures especially in Figures 11 & 12. If the authors conducted ANOVA and Tukey's test bars may be differentiated by varied letters.
Author Response
Comment 1: The authors addressed my comments and suggestions but the results of the statistical analysis should be presented on figures especially in Figures 11 & 12. If the authors conducted ANOVA and Tukey's test bars may be differentiated by varied letters.
Answer: The results of the statistical analysiswere presented on Figures 9, 10, 11 e 12 . ANOVA and Tukey's test were conducted and the means were differentiated by varied letters on the figures.
