Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains

Round 1

Reviewer 1 Report

Purpose of the research is to examine the sorption capacity of dispersed oil in wastewater (dispersed soybean oil in water by hydrophobized/oleophilized autoclaved aerated concrete. Results of the study may have important application in the wastewater treatment field.  Authors may wish to consider the following comments in revisions of their manuscript.

1.       Synthetic wastewater was used in the study.  Please comment on the effect of other contaminants present in real wastewater will have on the treatment performance.

2.       Please comment on the cost of proposed treatment methods.

3.       Please comment whether effluent from the proposed treatment method can meet effluent standards in author’s country.

4.       Please comment on the regeneration of spent adsorbents.

5.       Please compare results of your study with other similar studies reported in literature.

6.       Please comment on the limitation of the proposed treatment method.

Author Response

1. Synthetic wastewater was used in the study.  Please comment on the effect of other contaminants present in real wastewater will have on the treatment performance.

Thanks you for the comment. In this study, we used artificially-prepared “dispersed oily wastewater” using soybean oil that is common in domestic wastewater to examine the absorption capacity of AAC grains in a simple system (as a first step) . As in pointed out by the comment, we agree it is important to examine the other contaminants (especially, organic pollutants in domestic wastewater). We give the prospect in “Conclusions”.

2. Please comment on the cost of proposed treatment methods.

Basically, the materials cost of AAC scrap is zero because it was dumped as it. (it needs only the cost for preparing of material preparation such as crushing and sieving). The exact operation treatment cost has not yet been examined in this study, but, it is assumed that the operation cost will be equivalent to typical floating adsorption system. Thus, the total cost shall be lower than normal treatment method using manufactured adsorbents. Because we need more careful consideration on the cost benefit analysis on the treatment system and the discussion is out of scope in this manuscript, we like to examine it in future as another viewpoints.

3. Please comment whether effluent from the proposed treatment method can meet effluent standards in author’s country.

Figure 5 shows that the 70-90 removal percent at C_i=100 mg/L that meets the standard of 5-30 mg/L given in Water Pollution Prevention Act (1970) of Japan.

4. Please comment on the regeneration of spent adsorbents.

Thank you for the comment. In this manuscript, we did not discuss the regeneration of spent adsorbents. But, we have an idea on the regeneration, e.g., heating the spent adsorbents at 700 K (which is the boiling points of oleic acid and stearic acid, and sorbed dispersed oils). We are now examining the regeneration and could be shown in future work.

5. Please compare results of your study with other similar studies reported in literature.

Table 1 shows the comparison of tested results in this study to previous studies.

6. Please comment on the limitation of the proposed treatment method.

Thanks for the comment. We have not yet fully examined the limitation of the proposed treatment method. But, due to the previous works by authors (Matsuno and Kawamoto, 2022. Environments; [56] in the manuscript), the coating amounts of hydrophobic/oleophilic agents would control the limitation of the capacity of dispersed oil onto AAC grains.

Reviewer 2 Report

 

The manuscript "Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains" presents the batch sorption capacity tests of dispersed oil in wastewater onto the hydrophobized/oleophilized autoclaved porous aerated concrete (AAC) grains. The design of the study was clearly stated and the detailed methods were described. I appreciate that the Authors done the test of the dispersed oils. The aerated concrete grains have already been used for removal of oil from water (as also Authors mention in introduction). Therefore, the novelty of the study is low. Moreover, the manuscript contain too many Figures, which number should be reduced. My main concern is also lack of the repetitions - figures without at least standard deviation. The repetitions of the particular experiments increase quality of the study. I would also recommend the economic calculation that could support inexpensiveness of the presented method (including crushing, autoclaving etc).

Author Response

The manuscript "Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains" presents the batch sorption capacity tests of dispersed oil in wastewater onto the hydrophobized/oleophilized autoclaved porous aerated concrete (AAC) grains. The design of the study was clearly stated and the detailed methods were described. I appreciate that the Authors done the test of the dispersed oils. The aerated concrete grains have already been used for removal of oil from water (as also Authors mention in introduction). Therefore, the novelty of the study is low. Moreover, the manuscript contain too many Figures, which number should be reduced. My main concern is also lack of the repetitions - figures without at least standard deviation. The repetitions of the particular experiments increase quality of the study. I would also recommend the economic calculation that could support inexpensiveness of the presented method (including crushing, autoclaving etc).

 

Thank you for the comments. As given in the manuscript, very limited studies have been done the oily wastewater treatment using CDW origin adsorbents and the topic in this study is challengeable (originality and novelty). Besides, the adsorption characteristics of “dispersed oil in water” that has droplet size with < 2 μm  have not been fully studies (Note: many studies on oily wastewater treatment targets normal oil) All figs and tables are necessary to explain and to examine the tested data, and the tables in Appendix would give useful information and reference for other researchers. Regarding on the comment of economic calculation, see response to the comment No. 2 of Reviewer 1.

Reviewer 3 Report

Dear Author,

I read the manuscript environments-2268934-peer-review-v1: ” Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains”, and I present below a few of my observations:

 

 1.      In Figure 2: What does "frequency, %" mean and how is it defined? Isn't it a degree of recovery?

2.      Figures 7-8: Another scale could be chosen for the representation, so that the graphic arcs are suggestions. That's how they are very cramped and without meaning!!! There is only one point "lost" and the rest are crowded in the lower left. They must be redone!!!

 

The work is very thin in terms of analyzes and interpretations. It must be completed with characterization structures of the materials before and after adsorption. This study must be justified and motivated from a practical point of view. Retention mechanism?

 

In order to be published, it must be substantially improved/completed – Majore !

 

Sincerely yours,

Author Response

1. In Figure 2: What does "frequency, %" mean and how is it defined? Isn't it a degree of recovery?

 

Thanks for the comment. As indicated in Eq.(3), this shows how much C_e (equilibrium concentration) has decreased from the initial concentration C_i.

 

2. Figures 7-8: Another scale could be chosen for the representation, so that the graphic arcs are suggestions. That's how they are very cramped and without meaning!!! There is only one point "lost" and the rest are crowded in the lower left. They must be redone!!!

Thanks for the comment. We have revised the figures.

The work is very thin in terms of analyzes and interpretations. It must be completed with characterization structures of the materials before and after adsorption. This study must be justified and motivated from a practical point of view. Retention mechanism?

Thanks for the comment. We fully agree the comment. The mechanism of dispersed oil in water onto porous media is quite interesting and complicated (very limited studies). We like to challenge for understanding the mechanism, continuing the research work. Till now, as a first step, we have examined the removal percent and adoption of (typical) adsorption isotherm concept in this study.  

Round 2

Reviewer 2 Report

Dear authors, please  re-read my comments and respond to all of them. In addition, please supplement the introduction with a yours publication "Hydrophobicity/Oleophilicity of Autoclaved Aerated Concrete (AAC) Grains Coated with Oleic and Stearic Acids for Application as Oil/Water Separating Filtration and Adsorbent Materials in Vietnam" and provide an explanation about continuation of the studies. Previous comments:

"The aerated concrete grains have already been used for removal of oil from water (as also Authors mention in introduction). Therefore, the novelty of the study is low. Moreover, the manuscript contain too many Figures, which number should be reduced. My main concern is also lack of the repetitions - figures without at least standard deviation. The repetitions of the particular experiments increase quality of the study. I would also recommend the economic calculation that could support inexpensiveness of the presented method (including crushing, autoclaving etc)."

Author Response

Dear authors, please re-read my comments and respond to all of them. In addition, please supplement the introduction with a yours publication "Hydrophobicity/Oleophilicity of Autoclaved Aerated Concrete (AAC) Grains Coated with Oleic and Stearic Acids for Application as Oil/Water Separating Filtration and Adsorbent Materials in Vietnam"  and provide an explanation about continuation of the studies.

 

Previous comments:

"The aerated concrete grains have already been used for removal of oil from water (as also Authors mention in introduction). Therefore, the novelty of the study is low. Moreover, the manuscript contain too many Figures, which number should be reduced. My main concern is also lack of the repetitions - figures without at least standard deviation. The repetitions of the particular experiments increase quality of the study. I would also recommend the economic calculation that could support inexpensiveness of the presented method (including crushing, autoclaving etc)."

Answer: Thank you for the comments. As given in Introduction, AAC grains have been used to treat wastewater, but, those studies targeted the applicability of AAC grains to treat heavy metals (not dispersed oil examined in this study). Moreover, our previous study, Matsuno and Kawamoto (2022; Environments) characterized the surface hydrophobicity/oleophilicity of AAC grains coated with hydrophobic agents and did not examine the removal of dispersed oil treatment in water and adsorption characteristics (This paper is newly examining the topic).

Answer: Thanks again for the comments. According to the suggestions, we reduced the volume and numbers of Figures and Tables in the revised manuscript. Additionally, we added error bars of standard deviations (from triplicate measurements) in Figure 4 and Figure 5, and Figure 6. As shown in those figures, the small error bars (standard deviations) gave us a good reproductivity on the measurements (i.e., good repetitions).

Answer: Besides, as mentioned in our previous response to reviewers’ comments, this study mainly examined the adoptability and feasibility of dispersed oil treatment in water using grained AAC scrap (zero cost) in the laboratory tests. The detail economic cost analysis should be done as a next step (out of scope of this study) using a real-scale wastewater treatment system (e.g., floating adsorption system).  

Reviewer 3 Report

Dear Author,

I read the manuscript environments-2268934-peer-review-v1: ” Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains”, and I present below a few of my observations:

 

 

1.      In Figure 2: What does "frequency, %" mean and how is it defined? Isn't it a degree of recovery?

2.      Figures 7-8: Another scale could be chosen for the representation, so that the graphic arcs are suggestions. That's how they are very cramped and without meaning!!! There is only one point "lost" and the rest are crowded in the lower left. They must be redone!!!

 

The work is very thin in terms of analyzes and interpretations. It must be completed with characterization structures of the materials before and after adsorption. This study must be justified and motivated from a practical point of view. Retention mechanism?

 

In order to be published, it must be substantially improved/completed – Majore !

 Sincerely yours,

 

Author Response

I read the manuscript environments-2268934-peer-review-v1: ” Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains”, and I present below a few of my observations:

1. In Figure 2: What does "frequency, %" mean and how is it defined? Isn't it a degree of recovery?
   

   Answer: Thanks for the comment. As given in the manuscript, Figure 2 shows the particle size distributions of dispersed oil in water measured by a laser diffraction nanoparticle size distribution analyzer (SALD–7100, Shimadzu, Japan). In general, the frequency % distribution measured by the Nano Particle Size Distribution Analyzer shows the particle size distribution as 0-100% based on the "piece count standard". For example, In Nagai et al. (2015) (https://www.mdpi.com/120640),  Figure 1 shows the relationship between particle size and frequency.

2. Figures 7-8: Another scale could be chosen for the representation, so that the graphic arcs are suggestions. That's how they are very cramped and without meaning!!! There is only one point "lost" and the rest are crowded in the lower left. They must be redone!!!
   

   Answer: Thank for the comment. Following the suggestion, we have unified Figures 7 and 8 and redrawn the graphs with Y-axis in the range 0-12 mg/g, x-axis in the range 0-300 mg/L for Figures 7 (a)(c)(e) and 0-800 mg/L for Figures 7 (b)(d)(f).

   
   
   

3. The work is very thin in terms of analyzes and interpretations. It must be completed with characterization structures of the materials before and after adsorption. This study must be justified and motivated from a practical point of view. Retention mechanism?

   Answer: Thanks for the comment. We are understanding the comment. To clarify the retention mechanism means clarifying the adsorption mechanism on the surface layer, and it is needed further studies (as given in Conclusions). We plan to continue the studies using other approaching to clarify the sorption mechanism details (especially, the approaches based on stereochemistry using further elaborated techniques such as NMR and XPS.

Round 3

Reviewer 2 Report

The paper improved after the corrections and can be accepted for publication.

Author Response

1. The paper improved after the corrections and can be accepted for publication
   
   

   Answer: Thank you for the comment. Please see our revised manuscript.

Reviewer 3 Report

Dear Author,

I read the manuscript environments-2268934-peer-review-v3: ” Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains”, and I present below a few of my observations:

  1. „Thanks for the comment. As indicated in Eq.(3), this shows how much C_e (equilibrium concentration) has decreased from the initial concentration C_i.”

R. Until now, I have not come across such a term used for the evaluation of adsorption processes.... The efficiency of absorption processes is usually assessed by the adsorption capacity q (mg/g) or the degree of retention R% [(retained quantity / initial quantity) x100] – not „Frequency”  !!!! In figure 4, the expression is correct!!!

 2. Figures 7-8: Another scale could be chosen for the representation, so that the graphic arcs are suggestions. That's how they are very cramped and without meaning!!! There is only one point "lost" and the rest are crowded in the lower left. They must be redone!!!

R. It is ok. A much more in-depth explanation is needed for the behavior of the studied adsorbents against oil depending on their structure, respectively the applicability of the adsorption models. You gave examples from the literature, but there are behaviors that can be explained with the help of the Langmuir and Freundlich isotherm. Things seem to be random here. The explanation leaves the result of the study up in the air.....

 3. The data in Table 1 necessarily require a logical explanation.

 4. „Thanks for the comment. We fully agree the comment. The mechanism of dispersed oil in water onto porous media is quite interesting and complicated (very limited studies). We like to challenge for understanding the mechanism, continuing the research work. Till now, as a first step, we have examined the removal percent and adoption of (typical) adsorption isotherm concept in this study. „

R. For a paper in an iSI journal it is much too thin without more concrete data !!!

 

5. Concluzions, lines 288-290: This is not clear from what you wrote!!!

 

Although numerous corrections and improvements have been made to the manuscript, the last part (explanation of experimental data modeling using the 3 isotherm models) and the conclusions require greater attention and depth.

I still believe that major corrections are necessary !

 Sincerely yours,

Author Response

1. Until now, I have not come across such a term used for the evaluation of adsorption processes.... The efficiency of absorption processes is usually assessed by the adsorption capacity q (mg/g) or the degree of retention R% [(retained quantity / initial quantity) x100] – not „Frequency” !!!! In figure 4, the expression is correct!!!

Answer: Thanks for the comment. Yes, the adsorption capacity can be usually assessed by the indicators such as the max. adsorption capacity and removal percent (R). On the other hand, the adsorption models/theories should be carefully chosen depending on the mechanism of target mass/ions onto adsorbents. In this study, we target the adsorption of dispersed oil in water onto AAC grains. The adsorption mechanisms are complicated, and the related studies have not been fully examined. In this study, therefore, we used a simple indicator, R, to examine the adsorption capacity and to examine the application of typical adsorption isotherm models such as linear, Langmuir, and Freundlich.

2. It is ok. A much more in-depth explanation is needed for the behavior of the studied adsorbents against oil depending on their structure, respectively the applicability of the adsorption models. You gave examples from the literature, but there are behaviors that can be explained with the help of the Langmuir and Freundlich isotherm. Things seem to be random here. The explanation leaves the result of the study up in the air.....

Answer: Please see our response comments above (No 1).

3. The data in Table 1 necessarily require a logical explanation.

Answer: Thanks for the comment. We further revised the manuscript.

4. For a paper in an iSI journal it is much too thin without more concrete data !!!

Answer: Thanks for the comment. We fully understand your comment. As shown in “Introduction”, limited studies challenged to investigate the sorption of dispersed oil in water onto porous grains as adsorbents. Thus, it is worth to show the tested results in this manuscript to researchers and readers as a first step.  

*As shown in small error bars of standard deviations, the reproducibility of measurements is good in this study. And, as given in “Conclusions”, we understand well further studies and more careful consideration are needed to characterize the sorption mechanism and to determine the maximum sorption capacity of dispersed oil in water. As commented in the responses above, the accessibility of dispersed oil (considering the emulsification process) to porous grains and the affinity of dispersed oil on the cementitious adsorbents have to be examined to discuss the sorption mechanisms, utilizing more elaborated techniques and equipment under more control conditions.

5. Concluzions, lines 288-290: This is not clear from what you wrote!!!

Answer: We cannot see the suggested lines in the manuscript. But, now the conclusion is simple and clear.

Although numerous corrections and improvements have been made to the manuscript, the last part (explanation of experimental data modeling using the 3 isotherm models) and the conclusions require greater attention and depth.

Answer: Thank you for the comment. The relevant part of “Discussion” was revised to clarify more with simple (but strong) words. Additionally, we keep the “Conclusions” simple and clear as other reviewers gave no comments to the relevant parts.

Round 4

Reviewer 3 Report

Dear  Editor

 Dear Author,

I read the manuscript environments-2268934-peer-review-v4: ” Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains”, and I present below a few of my observations:

 1.       In equation 3 you defined R% as retention rate and not frequency!!! Nothing was corrected in the figure 2, the incorrect term "frequency" remained.

2.       Figures 7-8: The explanations on the models used have been completed. And yet the adsorption mechanism? Maybe it's not even about adsorption in the true sense....

3.       Table 1: Negative values for quantities that are necessarily positive are not relevant and necessary in this table!

4.       For a paper in an ISI journal it is much too thin without some more concrete data  aboul the adsorption mechanism!!!

5.       Concluzions: It is not understood what the practical conclusion of this study is. What was his purpose?

 

Although numerous corrections and improvements have been made to the manuscript, the last part (the explanation of the retention mechanism) and the conclusions need more attention.

 

I still believe that major corrections are necessary !

 Sincerely yours,

Author Response

1.       In equation 3 you defined R% as retention rate and not frequency!!! Nothing was corrected in the figure 2, the incorrect term "frequency" remained.   We amended it.

2. Figures 7-8: The explanations on the models used have been completed. And yet the adsorption mechanism? Maybe it's not even about adsorption in the true sense....   See our response to Editor’s comment   3. Table 1: Negative values for quantities that are necessarily positive are not relevant and necessary in this table!   See our response to Editor’s comment.   4. For a paper in an ISI journal it is much too thin without some more concrete data  aboul the adsorption mechanism!!!   See our response to Editor’s comment.    5. Concluzions: It is not understood what the practical conclusion of this study is. What was his purpose?   See our response to Editor’s comment.  

Round 5

Reviewer 3 Report

Dear Assistant Editor

 

Dear Author,  

I read the manuscript environments-2268934-peer-review-v5: ” Assessment of Dispersed Oil Sorption in Oily Wastewater onto Hydrophobized/Oleophilized Autoclaved Aerated Concrete (AAC) Grains”, and I present below a few of my observations:

 

 

1.       In equation 3 you defined R% as retention rate or „the removal percentage of dispersed oil in water” and NOT FREQUENCY!!! Nothing was corrected in the figure 2, the incorrect term "frequency" remained. - It seems that the authors do not understand or do not want to understand!

 

 

Sincerely yours,

Author Response

1. In equation 3 you defined R% as retention rate or „the removal percentage of dispersed oil in water” and NOT FREQUENCY!!! Nothing was corrected in the figure 2, the incorrect term "frequency" remained. - It seems that the authors do not understand or do not want to understand!

Answer: The "R" in "Removal %" is used in Figs. 4, 5, and 6, and “Not for Fig. 2”.

Again, generally, the frequency % distribution measured by the Nano Particle Size Distribution Analyzer shows the particle size distribution as 0-100%. particle size distribution as 0-100% based on the "piece count standard” (e.g., Nagai et al. (2015) (https://www.mdpi.com/120640).