Adsorption of Arsenic from Water Using Aluminum-Modified Food Waste Biochar: Optimization Using Response Surface Methodology
Round 1
Reviewer 1 Report
This manuscript deals with the optimization of synthesis conditions for the production of biochar from aluminum-containing food waste. The biochar with optimized synthesis conditions (3.5 h pyrolysis time, 468.36 ℃ pyrolysis temperature, and 6 w/w % of Al content) was exercised for its adscription performance towards arsenite through batch adsorption tests. The findings are interesting and original and the narrative is well-written. However, there are already few studies including from the same group (Reference 48) where the synthesis conditions are optimized using the response surface methodology (RSM) for the same type of food waste from food processing plant. I see a great overlap between this study and Ref. 48. In addition, I have few suggestions/comments.
1. In abstracts: the findings of RSM are missing. In addition, the significance of the reaction-based model is less and shall be taken out from abstract.
2. Arsenite (As(III)) is applied as model pollutant and As(III) shall be used instead of As in the whole manuscript.
3. Can synthesized adsorbent be used to treat raw groundwater for potable purposes?
4. What is the knowledge gap and hypothesis of this study?
5. Line 44: it is suggested to discuss the specific treatment technology with central materials involved instead of generalized information. For example, Ultrafiltraion (see, Chemie Ingenieur Technik 2021, 93, 1396-1400) is a membrane technology that has been investigated for arsenic removal and (Journal of Environmental Sciences 2015, 32, 42-53 using iron precipitation.)
6. Lines 55-56: Iron oxides (for example, Journal of Hazardous Materials, 2020, 123221) are famous for arsenic removal using to strong affinity shall be discussed. In addition, activated carbon is not a good adsorbent for arsenic removal.
7. Line 80: I am unable to find investigations on food waste biochar (FWB)
8. Line 95: How did you estimated that biochar’s modified with 0.25M ,0 5M and 0.75M AlCl3 contains 2,4 and 6 Al wt% in modified biochar?
9. Line 17: How the 17 number of trails are determined?
10. Line 216: It should be table 1.
11. The surface charge and specific (BET) surfaces for biochars prepared at different conditions are lacking.
12. Figure 1: The quality of this figure shall be improved.
13. Line 255-259: How can the adsorption capacity of biochar for As(III) continue to increase with increasing pH when the arsenite exist as uncharged specie (H3AsO3)? Deep discussion on this missing.
14. Line 289: Competitive ions having negative charge are not adsorbed by biochar. The author should critically discuss the insights that contribute to this behavior.
15. Lines 323-324: The nature of adsorption cannot be decided by just fitting the kinetic data with reaction-based based model. To determine the nature of adsorption. Various microscopic tools such as FTIR, XPS etc.
Author Response
Reviewer #1
This manuscript deals with the optimization of synthesis conditions for the production of biochar from aluminum-containing food waste. The biochar with optimized synthesis conditions (3.5 h pyrolysis time, 468.36 ℃ pyrolysis temperature, and 6 w/w % of Al content) was exercised for its adscription performance towards arsenite through batch adsorption tests. The findings are interesting and original and the narrative is well-written. However, there are already few studies including from the same group (Reference 48) where the synthesis conditions are optimized using the response surface methodology (RSM) for the same type of food waste from food processing plant. I see a great overlap between this study and Ref. 48. In addition, I have few suggestions/comments.
- In abstracts: the findings of RSM are missing. In addition, the significance of the reaction-based model is less and shall be taken out from abstract.
Answer) As your comments, the results obtained from the RSM study were added to the abstract. A part of the description of the reaction-based model was removed from the abstract.
- Arsenite (As(III)) is applied as model pollutant and As(III) shall be used instead of As in the whole manuscript.
Answer) I agree with your comments. The target contaminant in this study is As(III), and it should be preferred than As. Depending on the context, As was revised to As(III).
- Can synthesized adsorbent be used to treat raw groundwater for potable purposes?
Answer) The synthesized adsorbent can be applicable to treat groundwater because of its high efficiency under neutral and alkaline solution pH. The presence of anions such as nitrate, sulfate, and phosphate did not remarkably reduce its As(III) adsorption capacity. However, high concentration of carbonate noticeably reduced its As(III) adsorption, and such a condition should be considered for applying the Al-FWB.
- What is the knowledge gap and hypothesis of this study?
Answer) As you know, various kinds of adsorbents were tested for treating As(III), but aluminum-impregnated food waste biochar (Al-FWB) has never been studied for removing As(III) by other researchers. Previous studies reported that Al-FWB was efficient for removing anions such as fluoride, and we hypothesized that it could be also applicable to remove fluoride from contaminated water.
- Line 44: it is suggested to discuss the specific treatment technology with central materials involved instead of generalized information. For example, Ultrafiltraion (see, Chemie Ingenieur Technik2021, 93, 1396-1400) is a membrane technology that has been investigated for arsenic removal and (Journal of Environmental Sciences 2015, 32, 42-53 using iron precipitation.)
Answer) As your comments, the specific technology was mentioned in the revised manuscript by citing the references you suggested.
- Lines 55-56: Iron oxides (for example, Journal of Hazardous Materials, 2020, 123221)are famous for arsenic removal using to strong affinity shall be discussed. In addition, activated carbon is not a good adsorbent for arsenic removal.
Answer) As your comments, iron oxyhydroxides (Journal of Hazardous Materials, 2020, 123221) was listed as an adsorbent for removing arsenic. I also agree with that activated carbon is not a good adsorbent for arsenic removal because of its negative charge. However, the cited reference is the research on the application of not raw activated carbon but iron-modified activated carbon. In the revised manuscript (Line 57), the iron-modified activated carbon was specified.
- Line 80: I am unable to find investigations on food waste biochar (FWB)
Answer) Thanks for your delicate comments, the sentence in Line 81 was revised. “Equilibrium, kinetic, and thermodynamic adsorption model analyses were performed to further characterize the As(III) adsorption to Al-FWB.”
- Line 95: How did you estimated that biochar’s modified with 0.25M ,0 5M and 0.75M AlCl3 contains 2,4 and 6 Al wt% in modified biochar?
Answer) 0.25 M of AlCl3 is 6.75 g-Al/L and 300 mL of 0.25 M AlCl3 is 2.03 g of Al. 300 mL of AlCl3 solution (2.03 g of Al) was mixed with 100 g of food waste, and the weight percentage of Al is 2%.
- Line 17: How the 17 number of trails are determined?
Answer) 17 trials was determined by the Box-Behnken model in the RSM. 17 trials include five repetitive experiments at central points.
- Line 216: It should be table 1.
Answer) Thanks for your delicate comments. It was revised to “Table 1”.
- The surface charge and specific (BET) surfaces for biochars prepared at different conditions are lacking.
Answer) The specific surface area and pore volume of the biochar were added in the revised manuscript (Line 115-116 & 272-274).
- Figure 1: The quality of this figure shall be improved.
Answer) As your comments, the Figure 1 was replaced with the one with high resolution.
- Line 255-259: How can the adsorption capacity of biochar for As(III) continue to increase with increasing pH when the arsenite exist as uncharged specie (H3AsO3)? Deep discussion on this missing.
Answer) The pKa1 of H3AsO3 is 9.2, and 50% of H3AsO3 and 50% of H2AsO3- are present at pH 9.2 As the increase of solution pH, the H3AsO3 gradually turns into H2AsO3-. Therefore, the As(III) adsorption was increased not suddenly but gradually.
- Line 289: Competitive ions having negative charge are not adsorbed by biochar. The author should critically discuss the insights that contribute to this behavior.
Answer) As your comments, the effect of other ions not reacting with As was investigated and newly described in the revised manuscript (Line 333-338).
- Lines 323-324: The nature of adsorption cannot be decided by just fitting the kinetic data with reaction-based based model. To determine the nature of adsorption. Various microscopic tools such as FTIR, XPS etc.
Answer) As your comments, some of analyzing tools including FE-SEM, EDS, XRD, a specific surface analyzer, and FTIR were used to analyze the physical and chemical nature of the adsorbents. The results were additionally added in the revised manuscript (Line 261-280).
Reviewer 2 Report
Overall, I consider that there is a lack of novelty in this paper, besides it contains several drawbachs. The adsorbent used for As removal contained Al. Therefore, this material can not be used at low pH because of the release of Al in the solution. Authors have not analyzed this point in their paper. On the other hand, the adsorbent characterization is not reported and, consequently, there is no evidence to discuss the adsorption mechanism. The calculation of RL parameter from Langmuir model is meaningless because it is always between 0 and 1. Thermodynamic calculations are also incorrect. In summary, the paper rejection is strongly suggested.
Author Response
Reviewer #2
Overall, I consider that there is a lack of novelty in this paper, besides it contains several drawbachs. The adsorbent used for As removal contained Al. Therefore, this material can not be used at low pH because of the release of Al in the solution. Authors have not analyzed this point in their paper. On the other hand, the adsorbent characterization is not reported and, consequently, there is no evidence to discuss the adsorption mechanism. The calculation of RL parameter from Langmuir model is meaningless because it is always between 0 and 1. Thermodynamic calculations are also incorrect. In summary, the paper rejection is strongly suggested.
Answer) To the best our knowledge, the aluminum impregnated food waste biochar has never been studied for removing As(III) in aqueous solution. The authors believe that this study has some novelty to be published in this journal.
I agree with your comments that the Al-FWB has a problem regarding the release of Al from the adsorbent at low pH. However, it can be effective for removing As in neutral and alkaline solution.
As your comments, the adsorbent characterization was performed including FE-SEM, EDS, XRD, a specific surface analyzer, and FTIR. The results were additionally added in the revised manuscript (Line 261-280).
As your comments, the calculation of RL is not necessary for analyzing the equilibrium data. The description regarding RL was removed from the revised manuscript.
Reviewer 3 Report
Manuscript Number: water-1858679
Title: Adsorption of Arsenic from Water using Aluminum-modified Food Waste Biochar: Optimization using Response Surface Methodology
The authors used aluminum-impregnated food waste as a filter medium to remove As(III) from aqueous solutions and investigated the effects of several factors on the adsorption capacity of aluminum-modified food waste biochar (Al-FWB). In addition, the adsorption kinetics was modelled by using the pseudo-first order and pseudo-second order models. The results suggested that Al-FWB is a promising low-cost adsorbent for removing As(III) from aqueous solutions and managing food waste. Overall, this work has some innovation and can provide some interesting ideas to readers. There are not too many typos and grammatical errors. However, the Tables and Figures require great improvement. The specific comments are as follows:
1. Line 32, “by arsenic is” should be “by arsenic, is”
2. Line 34, “are the know” should be “are know”
3. Line 46, “requirement of” should be “requirement for”
4. Line 75, the composition of food waste used in this study should be more complex than the pure wastes used in the previous studies as described in lines 57-64. Even though they are all organic waste, the properties and composition of food waste from households should be greatly different from that of wood, rice husk and so on. The authors should provide more background regarding the current progress of using household food waste as raw materials for biochar production.
5. Line 82, response surface methodology was used to optimize the adsorbent preparation. The basic information regarding the response surface methodology and the corresponding advantages are suggested to be added to the introduction section.
6. Line 176, the 17 trials used in the response surface methodology study were the real experimental test results or theoretically calculated results?
7. Line 239, Figure 1, the image pixel is too low, please improve it in the revised manuscript.
8. Line 274, the Figure number is wrong, it should be “Figure 2”. In addition, the legend should not overlap the column and the axis label font is too large. The same problem in Figrue 3 to Figure 6. Please revise and improve them.
9. Figure 2 to Figure 6, the axis scale is too dense, and the image pixel require further improvement. Please revise them.
10. Line 328, the Table number should be 2. The authors should carefully check the serial numbers of the figures and tables throughout the manuscript.
11. Line 357, the font size in this Table is much larger than the text, please revise it.
12. Three-line watch Tables are primarily suggested in the manuscript, especially for Tables 5 and 6.
13. Line 390-391, “under the experimental conditions” should be “under experimental conditions”
Author Response
Reviewer #3
The authors used aluminum-impregnated food waste as a filter medium to remove As(III) from aqueous solutions and investigated the effects of several factors on the adsorption capacity of aluminum-modified food waste biochar (Al-FWB). In addition, the adsorption kinetics was modelled by using the pseudo-first order and pseudo-second order models. The results suggested that Al-FWB is a promising low-cost adsorbent for removing As(III) from aqueous solutions and managing food waste. Overall, this work has some innovation and can provide some interesting ideas to readers. There are not too many typos and grammatical errors. However, the Tables and Figures require great improvement. The specific comments are as follows:
Answer) On the behalf of my co-authors, I appreciate your valuable time to review our manuscript and give us valuable comments. The previously submitted manuscript has been edited by the Editage, a division of Cactus Communications (Service number HANT_747). However, we carefully checked the revised manuscript to find some errors and improve the English of the revised manuscript.
- Line 32, “by arsenic is” should be “by arsenic, is”
Answer) It was revised. Thanks for your delicate comments.
- Line 34, “are the know” should be “are know”
Answer) It was revised.
- Line 46, “requirement of” should be “requirement for”
Answer) It was revised.
- Line 75, the composition of food waste used in this study should be more complex than the pure wastes used in the previous studies as described in lines 57-64. Even though they are all organic waste, the properties and composition of food waste from households should be greatly different from that of wood, rice husk and so on. The authors should provide more background regarding the current progress of using household food waste as raw materials for biochar production.
Answer) As your comments, it was noticed that the food waste used in this study is obtained from the actual food waste collected from food waste treatment plants
“Not artificially selected single source of food waste but the actual food waste collected from food waste treatment plants were used.”
- Line 82, response surface methodology was used to optimize the adsorbent preparation. The basic information regarding the response surface methodology and the corresponding advantages are suggested to be added to the introduction section.
Answer) The advantage of the response surface methodology was newly described in the revised manuscript. Line 85-87.
- Line 176, the 17 trials used in the response surface methodology study were the real experimental test results or theoretically calculated results?
Answer) The 17 trials used in the RSM study were the real experimental test results. As your comments, it was noticed.
- Line 239, Figure 1, the image pixel is too low, please improve it in the revised manuscript.
Answer) As your comments, the quality of Figure 1 was revised and provided in the revised manuscript.
- Line 274, the Figure number is wrong, it should be “Figure 2”. In addition, the legend should not overlap the column and the axis label font is too large. The same problem in Figrue 3 to Figure 6. Please revise and improve them.
Answer) Thanks for your delicate comments. It was revised.
- Figure 2 to Figure 6, the axis scale is too dense, and the image pixel require further improvement. Please revise them.
Answer) As your comments, Figure 2 –6 were replaced by the ones with high resolution.
- Line 328, the Table number should be 2. The authors should carefully check the serial numbers of the figures and tables throughout the manuscript.
Answer) I am sure that Table 3 is correct because Table 3 lists the variables obtained from kinetic model analysis. As your comments, the numbers of figure and tables were checked.
- Line 357, the font size in this Table is much larger than the text, please revise it.
Answer) Thanks for your delicate comments. It was revised.
- Three-line watch Tables are primarily suggested in the manuscript, especially for Tables 5 and 6.
Answer) As your comments, Table 5 and 6 were revised.
- Line 390-391, “under the experimental conditions” should be “under experimental conditions”
Answer) As your comments, “under the experimental conditions” was revised to “under experimental conditions”
Reviewer 4 Report
The article presents very important topics about adsorption of arsenic from water using aluminum-modified food waste biochar. Unfortunately the authors did not avoid mistakes. Below is a list of things to fix:
In the introduction, there was no information on the methods of treating groundwater in such a way that it would be safe to drink, this is a very interesting topic. I propose to use the following literature:
DOI 10.12911/22998993/85373; 10.5004/dwt.2018.22551
Some of the materials and methods are missing a diagram of the experiment, photos of the sorbent and a description of its properties.
The Discussion of results section should be added, where the results will be compared with the other sorbent.
Author Response
Reviewer #4
The article presents very important topics about adsorption of arsenic from water using aluminum-modified food waste biochar. Unfortunately the authors did not avoid mistakes. Below is a list of things to fix:
Answer) On the behalf of my co-authors, I appreciate your valuable time to review our manuscript and give us valuable comments.
In the introduction, there was no information on the methods of treating groundwater in such a way that it would be safe to drink, this is a very interesting topic. I propose to use the following literature:
DOI 10.12911/22998993/85373; 10.5004/dwt.2018.22551
Answer) As your comments, the reference you suggested was cited in the revised manuscript.
Some of the materials and methods are missing a diagram of the experiment, photos of the sorbent and a description of its properties.
Answer) As your comments, the SEM images of adsorbents were added in the revised manuscript. The physical and chemical properties of adsorbents were analyzed using FE-SEM, EDS, XRF, FT-IR, and a specific surface analyzer. The results were newly provided in the revised manuscript (Line 261-280).
The Discussion of results section should be added, where the results will be compared with the other sorbent.
Answer) As your comments, the discussion part, especially the impact of other anions on As(III) adsorption, was improved. The As(III) adsorption capacity of Al-FWB was compared to that of other adsorbents reported in the literature, as listed in Table 5.
Round 2
Reviewer 1 Report
The authors have provided the necessary revisions but there are some comments that shall be discussed.
Your response: "0.25 M of AlCl3 is 6.75 g-Al/L and 300 mL of 0.25 M AlCl3 is 2.03 g of Al. 300 mL of AlCl3 solution (2.03 g of Al) was mixed with 100 g of food waste, and the weight percentage of Al is 2%." So, according to your response, it seems that the entire Al in solution was deposited on the synthesized adsorbent. Did you verify the amount of Al actually deposited with some analytical technique like X-ray fluorescence?
Figure 5: As you have mentioned that the pKa1 of H3AsO3 is 9.2. Then how can the amount of adsorbed As(III) increase at (final) pH below 9.2?
Following the same comment: There is a strong deviation in initial and final pH, especially in the acidic range. A reasonable explanation of this deviation shall be provided.
Author Response
Reviewer #1
The authors have provided the necessary revisions but there are some comments that shall be discussed.
Answer) On the behalf of my co-authors, I appreciate your valuable time to review our manuscript and give us valuable comments.
Your response: "0.25 M of AlCl3 is 6.75 g-Al/L and 300 mL of 0.25 M AlCl3 is 2.03 g of Al. 300 mL of AlCl3 solution (2.03 g of Al) was mixed with 100 g of food waste, and the weight percentage of Al is 2%." So, according to your response, it seems that the entire Al in solution was deposited on the synthesized adsorbent. Did you verify the amount of Al actually deposited with some analytical technique like X-ray fluorescence?
Answer) Thanks for your comments. The elemental composition of Al-FWB including Al was analyzed using an energy dispersive spectrometer (EDS) and an X-ray fluorescence (XRF) spectrometer. The results were provided in Line 268-272 and Table 3.
Figure 5: As you have mentioned that the pKa1 of H3AsO3 is 9.2. Then how can the amount of adsorbed As(III) increase at (final) pH below 9.2?
Answer) The pKa1 of H3AsO3 is 9.2. The H3AsO3 turn into H2AsO3- near pH 9.2 not suddenly but gradually. Therefore, the H3AsO3 can be present above pH 9.2, and the H2AsO3- also can be present below pH 9.2. We provided the Minteq simulation result below.
Following the same comment: There is a strong deviation in initial and final pH, especially in the acidic range. A reasonable explanation of this deviation shall be provided.
Answer) The strong deviation in initial and final pH was explained in the revised manuscript (Line 300-302).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
I still consider that the contribution of this paper is very limited. Authors have not provided proper responses for the review process. Therefore, its rejection is suggested.
Author Response
Reviewer #2
I still consider that the contribution of this paper is very limited. Authors have not provided proper responses for the review process. Therefore, its rejection is suggested.
Answer) We tried our best to answer the reviewer’s comments point by point.
Reviewer 3 Report
The comments regarding the Figure revision were not satisfactory solved. Fig. 3, the axis label font is too small and not clear. Fig. 5, the legend should not overlap the column. Fig. 5 to Fig. 9, the axis scale is too dense. The authors should resolve all comments carefully.
Author Response
Reviewer #3
The comments regarding the Figure revision were not satisfactory solved. Fig. 3, the axis label font is too small and not clear. Fig. 5, the legend should not overlap the column. Fig. 5 to Fig. 9, the axis scale is too dense. The authors should resolve all comments carefully.
Answer) On the behalf of my co-authors, I appreciate your valuable time to review our manuscript and give us valuable comments.
In Fig. 3, the axis label font was revised.
In Fig. 5, the legend was moved not to overlap the column.
The axis scale of Fig. 5-9 was revised not to be dense.
All your comments were carefully reflected in the revised manuscript.
