Cost-Effective Natural Adsorbents for Remediation of Oil-Contaminated Water

Round 1

Reviewer 1 Report (Previous Reviewer 3)

The authors have made thoughtful and complete revision in the spirit of the comments made. I think the new content addresses the concerns raised and also enriches the presentation. I support publication in the manuscripts' current form.

Author Response

Dear Reviewer,

Thank you very much for improving our manuscript.

We have attached a separate response to reviewers file

Thank you!

Author Response File: Author Response.docx

Reviewer 2 Report (New Reviewer)

Oily water is regarded as one of the most serious 23 environmental threats and is harmful to many life forms due to its toxicity.  The work is very useful to solve the problems.

Author Response

Dear Reviewer,

Thank you very much for improving our manuscript.

We have attached a separate response to reviewers file

Thank you!

Author Response File: Author Response.docx

Reviewer 3 Report (New Reviewer)

water-2253225                                                                                                 

Research Paper   

Title: Cost-effective Natural Adsorbents for Remediation of Oil Contaminated Water

 

Authors: Al-Najar et al.

 

General]

The authors used natural adsorbents for the adsorptive removal of oil from aqueous solutions. The manuscript can be considered for publication, subject to significant corrections.

 

Specifics]

1] The manuscript needs professional English proofreading due to strange lexical choices and incorrect grammar in several spots.

 

2] The y-axis titles in Figures 9 and 10 should be weight (%). There cannot be 100% mass change at room temperature.

 

3] The y-axis title of Figure 14 should be q_e.

 

4] The y-axis title of Figure 16 should be q_t instead of q_e as the measured capacity is at a given time (t) and not at equilibrium.

 

5] The adsorption kinetics section mentions Figure 12, while Figure 16 represents q_t versus time. The authors should check each figure number and corresponding citations in the main text.  

 

6] The authors must add non-linear adsorption kinetics, thermodynamics, and isotherm modeling to elucidate the prevalent mechanisms. The forceful linearization of inherently non-linear equations induces mathematical bias and leads to incorrect conclusions. Please refer to the following references (Note that there is no obligation to cite these references. These articles are recommended for learning purposes.): (i) El-Khaiary and Malash, 2011. Hydrometallurgy. 105 (3-4), 314-320, (ii) Lima et al., 2021. Journal of Environmental Chemical Engineering. 9 (2), 104813, (iii) Foo and Hameed, 2010. Chemical Engineering Journal. 156 (1), 2-10, (iv) Tran et al., 2017. Water Research. 120, 88-116, (v) Tan and Hameed, 2017. Journal of the Taiwan Institute of Chemical Engineers. 74, 25-48, (vi) Lima et al., 2020. Journal of Molecular Liquids. 311, 113315, and (vii) González-López et al., 2021. Separation & Purification Reviews. 51 (3), 358-372.

 

7] The PFO and PSO models do not have any physical meaning (e.g., physical and chemical adsorption (Tran et al., 2017. Water Research. 120, 88-116 and Tan and Hameed, 2017. Journal of the Taiwan Institute of Chemical Engineers. 74, 25-48)). The authors should update the discussion in Section 3.7 (adsorption kinetics) to avoid attaching physical meaning to simple mathematical kinetic equations. Also, the PFO and PSO models should not be attributed to Lagergren or Ho (Tran et al., 2017. Water Research. 120, 88-116).

 

8] The oil adsorption performance of a commercial activated carbon should be added as a control group.

 

9] The BET, micropore, and external surface area data should be provided for the tested adsorbents.

 

10] The pore size distribution data should also be provided for the tested adsorbents.

 

11] All experiments should be repeated to ensure data reproducibility. Vertical error bars should be added to each data point.

 

12] The oil adsorption performance in the co-presence of competing species should be added to the manuscript.

 

13] The XPS data should be provided before and after dye adsorption to propose a suitable mechanism.

 

14] The oil adsorption performance as a function of solution pH should be added to the manuscript.

 

15] The point of zero charge data of the tested adsorbents should be added to the manuscript.

 

 

Author Response

Dear Reviewer,

Thank you very much for improving our manuscript.

We have attached a separate response to reviewers file

Thank you!

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report (New Reviewer)

The authors have failed to address several of my comments. The manuscript is recommended to be rejected for further consideration.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

In the presented article, the possibility of using the remains of animals and plants for the adsorption of oil from water is considered. In this article, the attention of the authors was attracted by accessible and inexpensive materials, which really increases the practical significance of the study. However, the studied materials (AB and AR) were characterized only by IR spectra, and a very scarce amount of data was used to study the parameters of the adsorption process in order to draw reasonable conclusions.

In order for the idea of ​​the practical use of animal and plant remains proposed by the authors to have scientific significance, the article needs to be improved. I want to highlight the following points that require attention:

Introduction

1. In the introduction from lines 50 to 63, the information is taken from reference 14. I think it would be better not to take a large piece of information from one article, so as not to run into plagiarism.

2. The introduction does not reflect why exactly AB and AR are of interest and were studied by the authors of the article. Is the adsorption properties of AB and AR materials studied for the first time? If so, it would be good to emphasize the novelty of the study in the introduction.

 

Materials and methods

3. The authors indicated that they received samples of crude oil from a refinery company. I believe that this information is insufficient to characterize the reagent, since it is not indicated from which fields this oil came from. And the fractional composition of oil does not depend on the processing company, but on the place of origin.

4. Which animal bones were used? Was it the bones of birds, cows, pigs, or a mixture of different bones? The bones of birds and mammals have different density and porosity, which can significantly affect the surface area of ​​the resulting material.

5. What is anise residue? Is it the remains of fruits, stems or leaves? What part of the plant is used? Why did anise attract the attention of the authors, and not other plant waste?

6. Why is it necessary to wash the bones of animals in an alkali solution? Why hasn't this been done for anise residues? 15% alkali is a very dangerous reagent that can enter the environment when washing bones. Is it possible to avoid the stage of soaking in alkali?

7. In line 112, the authors write that they shook the adsorbent for 5 minutes and left it in contact for 30 minutes. Is this enough time to reach equilibrium? Judging by Figure 10, this is not enough to establish equilibrium. Can we trust the results in Figure 5 in this case?

8. Data on the conditions for recording IR spectra should be transferred from the discussion part (line 131) to the description of methods. Spectrum recording method (ATR or KBr pellet?) must be specified. You must specify the resolution used when registering the spectrum (resulution is more important than the spectrum range).

 

Results and discussion

9. My most important remark is that the properties of adsorbents are very poorly characterized in this work. The specific surfaces of adsorbents have not been measured, and there is no information on their particle size and chemical composition. These parameters are very important for adsorption materials, and otherwise it is impossible to explain the difference in the adsorption capacity of materials.

10. When studying the functional groups of adsorbents by the FTIR method, the authors did not indicate how much adsorbent was used in 400 mg/l oily water. This is important to indicate whether the adsorbent is saturated with oil or not.

11. In Figures 1-4, the authors labeled the absorption band maxima of the materials with high accuracy (6 significant digits). With what resolution were the IR spectra recorded? Does the resolution of the spectrum make it possible to indicate the maxima of the bands with such accuracy?

12. Have the bands in the IR spectrum been assigned based on any literature data? Are IR data available for similar materials with which to compare the data in this article? Or was the assignment of bands characteristic of different groups according to some book? It is necessary to provide references to the used literature.

13. Animal bones usually contain a lot of calcium phosphate. Were there any absorption bands of phosphate groups in the IR spectra?

14. I think that if the maxima of the absorption bands change little after adsorption, it would be convenient if the authors put the IR spectra of the materials before and after adsorption on the same plot, so that the change in the intensity ratio of the bands becomes more obvious. It is acceptable to normalize the spectra to make them of the same intensity. Otherwise, it is now very difficult to assess which lanes have changed and which have not. However, in this case, I only recommend this change and leave the final decision to the authors.

15. Figures 3 and 4 are both signed as spectra "after" oil adsorption. Probably a typo here.

16. The authors in tables 1 and 2 describe the presence of C=C bending oscillations. Unfortunately, for two atoms there is only stretching vibration. For bending to exist, a group of at least three atoms is required.

17. In addition, table 2 shows “C-H” bending vibrations, why are there no such bands in sample 1?

18. Based on the fact that "the location range of the peaks did not change", the authors concluded that the adsorption of oil on the surface of the studied materials is physical. First, it is not clear why such a conclusion was written only after the description of the IR spectra of AB, whether there is a difference in the nature of adsorption on the surface of the two materials. Secondly, the authors gave in the introduction to their article a detailed description from reference 14, how many different forces can provide the physical interaction of the adsorbent and adsorbate, but they themselves do not say what kind of interactions of oil and adsorbent they observe. To accurately show whether adsorption is a consequence of chemical or physical interaction, it is necessary not only to compare the spectra of adsorbents before and after the reaction, but also to identify which bands have changed. It is also necessary to bring the IR spectrum of the oil used in the experiment. Then it will be immediately clear whether the spectrum of the adsorbent after the reaction with oily water is a superposition of the spectra before the interaction and the spectrum of oil, or vice versa, contains new bands indicating chemical interaction. This will greatly improve the scientific significance of the work. If the IR spectra were taken in ATR mode, then you can easily get the spectrum of the liquid oil you used. However, since oil is a natural raw material, the composition of which depends on the field, please make a spectrum of the same reagent that you used in this article.

19. How was the adsorbent dried after the reaction with oily water before recording IR spectra?

20. At what temperature was the adsorption isotherm studied?

21. In line 176, the authors wrote that they used from 0.2 to 2 g of the adsorbent. However, in Figure 5, a point equal to 0 g of adsorbent and 0% oil removal is indicated. Has such a control experiment actually been carried out? This point is important because it indicates a possible error of the method and a change in the concentration of oil in the experiment due to adsorption on the walls of the dishes and during filtration. It can also affect the shape of the adsorption isotherm (Fig. 8)

22. Table 3 shows various parameters for the approximation of experimental data by the Langmuir and Freundlich equations. Are the authors sure that when using only 4 (or 5 if the point with zero amount of adsorbent was made) they can give the results of the approximation parameters with an accuracy of 6 significant digits? I believe that using only 4 experimental points without specifying a confidence interval is not enough to construct an adsorption isotherm and derive a statistically significant difference between the descriptions of the two theoretical models.

23. In lines 293-298, the authors describe the conditions of the experiment to determine the kinetic parameters of adsorption on the surface of AB and AR and do not talk about the shaking of the mixture mentioned earlier in line 112. How important is shaking and has it been used in studying adsorption kinetics?

 

Conclusion

24. The phrase in the conclusion that the materials used are cheap may be correct, but does not follow from the results of the presented article.

 

Despite the fact that in the present work the processes of oil adsorption important for practical application are studied, scientific conclusions about the correspondence of the Langmuir or Freundlich models may turn out to be statistically insignificant. The IR spectroscopy data require revision and more thorough analysis. Also, in discussing the results, it would be useful to compare the properties of the adsorbents studied in this study with other similar adsorbents of plant and animal origin. However, the idea of ​​the article is interesting and after setting up additional experiments and their more accurate processing, it can improve significantly.

Author Response

Dear Reviewer,

Thank you very much for the recommendations. We request you to please kindly check the attached response to reviewers file.

Reviewer 1

Introduction

1. In the introduction from lines 50 to 63, the information is taken from reference 14. I think it would be better not to take a large piece of information from one article, so as not to run into plagiarism.

Response

We sincerely thank the reviewer for pointing out this obvious mistake. We have now paraphrased and rewritten the section based on the reviewer's suggestion as follows:

 

The process by which oil molecules are attracted to the surface of a sorbent is referred to as oil adsorption [15]. Adsorption is primarily controlled by a variety of different phys-ical forces, the most important of which are the “Van der Waals forces, hydrophobicity, hydrogen bonding, polarity and steric interactions, dipole-induced dipole interactions, and π−π interactions” [16]. Because of its low processing cost and straightforward process design, adsorption is frequently utilised to treat oily water effectively. The process is driv-en by the attractive force between the sorbent's outer surface and the sorbate, which causes the sorbate molecules to aggregate on the sorbent's surface without actually penetrating the sorbent [17]. In general, there are three stages to the adsorption of oil: the dispersion of oil molecules into the surface of the sorbent, their trapping in the sorbent framework via capillary action, and the aggregation of oil droplets within the porous and rough structure of the sorbent [16].

 

2. The introduction does not reflect why exactly AB and AR are of interest and were studied by the authors of the article. Is the adsorption properties of AB and AR materials studied for the first time? If so, it would be good to emphasise the novelty of the study in the introduction.

Response

We used AB and AR as natural materials without treatment to save money on the treatment process. We looked for many natural substances that had not previously been tested in the literature to remove oil, and these two were the ones we chose.

We have added the following to the introduction section based on reviewers suggestions:

The novelty of this research is that the two natural substances, animal bones (ABs) and anise residues (ARs), have not been used in the past to remove oily pollutants from water. Furthermore, the research is beneficial from an environmental standpoint, as it reduces waste by converting these into useful substances.

 

 

 

Materials and methods

3. The authors indicated that they received samples of crude oil from a refinery company. I believe that this information is insufficient to characterise the reagent, since it is not indicated from which fields this oil came from. And the fractional composition of oil does not depend on the processing company, but on the place of origin.

Response

We thank the reviewer for the comment. The crude oil ws from Basrah field (API 30.5) of Iraq. We have added this information to the revised manuscript based on reviewers suggestion.

 

4. Which animal bones were used? Was it the bones of birds, cows, pigs, or a mixture of different bones? The bones of birds and mammals have different density and porosity, which can significantly affect the surface area of ​​the resulting material.

Response

 

We thank the reviewer for the comment. It's a fish scales bone. Fish scales are formed of bone from the deeper, or dermal, skin layer as such it was termed animal bone. Fish scales are composed of a surface layer containing hydroxyapatite (HA), calcium carbonate and a deeper layer made up of mostly collagen. Hydroxyapatite (HA) is a calcium phosphate mineral contained in normal bone.

 

 

5. What is anise residue? Is it the remains of fruits, stems or leaves? What part of the plant is used? Why did anise attract the attention of the authors, and not other plant waste?

 

Response

 

We thank the reviewer for the comment. Anise residue is the remains of anise seeds left after the oil extraction. These residues remain as waste.

Anise seed is used as a flavouring agent and in hot beverages. It tastes sweet and fragrant, similar to black licorice.

The authors are drawn to anise because it has not previously been used, as well as because it is readily available and inexpensive. It is popular in most Arabic countries as a hot drink and food, and it has health benefits. Yanson is the Arabic word for it.

 

 

 

6. Why is it necessary to wash the bones of animals in an alkali solution? Why hasn't this been done for anise residues? 15% alkali is a very dangerous reagent that can enter the environment when washing bones. Is it possible to avoid the stage of soaking in alkali?

 

Response

 

We thank the reviewer for the comment. Alkaline solutions, such as sodium hydroxide, were used to wash animal bones (ABs) in order to kill various viruses, remove impurities, fat, proteins, and tissues, and remove excess fat and protein.

Bones are washed and treated with chemicals such as sodium hydroxide, potassium hydroxide or acetic acid to remove impurities, proteins, fat and other tissues. According to reported studies in the literature, the animal bones derived HA material can become up to 30% more porous and improved surface modification after acid or alkali treatment [1].

[1] Abarasi Hart, Komonibo Ebiundu , Ebikapaye Peretomode , Helen Onyeaka, Ozioma Forstinus Nwabor and KeChrist Obileke, 2022, Value-added materials recovered from waste bone biomass: technologies and applications, RSC Adv., 2022, 12, pp.22302-22330,

 

7. In line 112, the authors write that they shook the adsorbent for 5 minutes and left it in contact for 30 minutes. Is this enough time to reach equilibrium? Judging by Figure 10, this is not enough to establish equilibrium. Can we trust the results in Figure 5 in this case?

Response

 

We thank the reviewer for pointing out this obvious typographical error. The time is 60 min, not 30 min so in the line, it corrected to:

Then these flasks were shaken for 60 min.

 

 

8. Data on the conditions for recording IR spectra should be transferred from the discussion part (line 131) to the description of methods. Spectrum recording method (ATR or KBr pellet?) must be specified. You must specify the resolution used when registering the spectrum (resulution is more important than the spectrum range).

 

Response

 

We thank the reviewer for the suggestion provided. We have now moved the whole paragraph to section 2 of the revised manuscript as follows:

Spectrophotometry is one of the important techniques in the diagnosis of different materials and is characterised by the fact that its performance is simple, fast, and cheap. This technique is used to identify hydrogen bonds, functional groups and chemical bonds [1]. In the present work, the functional groups present in ABs and ARs before and after the adsorption of oil were investigated by FTIR (BRUKER/Germany) analysis to identify changes that may occur in the vibrational frequency of the functional group of the adsorbents after adsorption of oil. The FTIR spectrum measurement was recorded in the wavenumber range of 600-4000 cm^--1. The spectrum recording method employed was the attenuated total reflectance (ATR) method with a resolution of 0.085 cm^-1.

 

Results and discussion

9. My most important remark is that the properties of adsorbents are very poorly characterised in this work. The specific surfaces of adsorbents have not been measured, and there is no information on their particle size and chemical composition. These parameters are very important for adsorption materials, and otherwise it is impossible to explain the difference in the adsorption capacity of materials.

 

Response

 

 

We thank the reviewer for this important comment. We would have liked to address the reviewer's concerns fully; however, the adsorbents were used up completely. As such, we could not address this here. We sincerely apologise for that. We will definitely do the suggested measurements in our future studies. As for the size and chemical composition, please find the details as follows:

 

The size of the particles of the two adsorbents was ‘fine’.

Chemical composition:

ABs : it contains calcium carbonate and hydroxyapatite [1]. Hydroxyapatite is also called hydroxylapatite (HA).

ARs: Aniseed contains 1.5–6.0 mass % of a volatile oil consisting primarily of trans-anethole and also as much as 8–11 mass % of lipids rich in fatty acids, such as palmitic and oleic acids, as well as approximately 4 mass % of carbohydrates, and 18 mass % of protein [2].

[1] Pon-On, W.; Suntornsaratoon, P.; Charoenphandhu, N.; Thongbunchoo, J.; Krishnamra, N.; Tang, I.M. Hydroxyapatite from fish scale for potential use as bone scaffold or regenerative material. MaterialsScience and Engineering: C 2016, 62, 183-189.

[2] Shojaii, A.; Abdollahi Fard, M. Review of Pharmacological Properties and Chemical Constituents of Pimpinella anisum. ISRN Pharm 2012, 2012, 510795, doi:10.5402/2012/510795.

 

10. When studying the functional groups of adsorbents by the FTIR method, the authors did not indicate how much adsorbent was used in 400 mg/l oily water. This is important to indicate whether the adsorbent is saturated with oil or not.

Response

 

We thank the reviewer for this important comment. The adsorbent used was 1g / 50 ml in 400mg/l solution.

 

11. In Figures 1-4, the authors labeled the absorption band maxima of the materials with high accuracy (6 significant digits). With what resolution were the IR spectra recorded? Does the resolution of the spectrum make it possible to indicate the maxima of the bands with such accuracy?

Response

 

We thank the reviewer for this important comment. FTIR spectrometer used in our work is manufactured by BRUKER/Germany and has a resolution of 0.085 cm^-1.

 

12. Have the bands in the IR spectrum been assigned based on any literature data? Are IR data available for similar materials with which to compare the data in this article? Or was the assignment of bands characteristic of different groups according to some book? It is necessary to provide references to the used literature.

Response

 

We thank the reviewer for this observation. FTIR bands are assigned from FTIR tables in the university laboratory and are done by the technician in charge of the device. Since it is a novel material, the spectra is not assigned based on any literature.

 

 

13. Animal bones usually contain a lot of calcium phosphate. Were there any absorption bands of phosphate groups in the IR spectra?

Response

 

We thank the reviewer for this observation. We have termed fish scales as ABs, which contain calcium carbonate and hydroxyapatite. Hydroxyapatite is also called hydroxylapatite (HA). This has been reflected in the relevant IR spectra.

 

14. I think that if the maxima of the absorption bands change little after adsorption, it would be convenient if the authors put the IR spectra of the materials before and after adsorption on the same plot, so that the change in the intensity ratio of the bands becomes more obvious. It is acceptable to normalise the spectra to make them of the same intensity. Otherwise, it is now very difficult to assess which lanes have changed and which have not. However, in this case, I only recommend this change and leave the final decision to the authors.

Response

 

The following figures after putting before and after adsorption in the same place:

 

 

 

Figure 1. FTIR spectrum for ABs before and after adsorption of oil.

 

 

Figure 2. FTIR spectrum for ARs before and after adsorption of oil.

 

15. Figures 3 and 4 are both signed as spectra "after" oil adsorption. Probably a typo here.

Response

 

We thank the reviewer for pointing out the obvious typographical error. It has now been corrected. Fig. 3 before adsorption and Fig.4 after adsorption.

 

16. The authors in tables 1 and 2 describe the presence of C=C bending oscillations. Unfortunately, for two atoms there is only stretching vibration. For bending to exist, a group of at least three atoms is required.

Response

 

We thank the reviewer for this suggestion. It has been corrected to stretching vibration.

17. In addition, Table 2 shows “C-H” bending vibrations, why are there no such bands in sample 1?

Response

 

We thank the reviewer for this observation. We would like to point out that C-H bending is not found in Figs 1 & 2, so it does not appear in Table 1.

 

 

18. based on the fact that "the location range of the peaks did not change", the authors concluded that the adsorption of oil on the surface of the studied materials is physical. First, it is not clear why such a conclusion was written only after the description of the IR spectra of AB, whether there is a difference in the nature of adsorption on the surface of the two materials. Secondly, the authors gave in the introduction to their article a detailed description from reference 14, how many different forces can provide the physical interaction of the adsorbent and adsorbate, but they themselves do not say what kind of interactions of oil and adsorbent they observe. To accurately show whether adsorption is a consequence of chemical or physical interaction, it is necessary not only to compare the spectra of adsorbents before and after the reaction, but also to identify which bands have changed. It is also necessary to bring the IR spectrum of the oil used in the experiment. Then it will be immediately clear whether the spectrum of the adsorbent after the reaction with oily water is a superposition of the spectra before the interaction and the spectrum of oil, or vice versa, contains new bands indicating chemical interaction. This will greatly improve the scientific significance of the work. If the IR spectra were taken in ATR mode, then you can easily get the spectrum of the liquid oil you used. However, since oil is a natural raw material, the composition of which depends on the field, please make a spectrum of the same reagent that you used in this article.

 

Response

 

We thank the reviewer for pointing this out. We have now excluded the conclusion based on the reviewer's suggestion.

 

 

19. How was the adsorbent dried after the reaction with oily water before recording IR spectra?

 

Response

 

We thank the reviewer for the comment. The absorbent material is dried after the oil absorption process in the oven to remove any moisture from the adsorbent material completely, and then the infrared specification is recorded. This step is performed by the technician.

 

 

 

20. At what temperature was the adsorption isotherm studied?

 

Response

 

We thank the reviewer for the comment. The adsorption isotherm study was performed at room temperature (25℃) in Iraq. And I mentioned that in the title of figures 6, 7, and 8.

 

21. In line 176, the authors wrote that they used from 0.2 to 2 g of the adsorbent. However, in Figure 5, a point equal to 0 g of adsorbent and 0% oil removal is indicated. Has such a control experiment actually been carried out? This point is important because it indicates a possible error of the method and a change in the concentration of oil in the experiment due to adsorption on the walls of the dishes and during filtration. It can also affect the shape of the adsorption isotherm (Fig. 8)

Response

 

Point 0 is just the origin between the x and y axes, and is not a measurement point. This means that at time 0, there is no additive to the solution and no adsorption, so the percentage removal is 0%.

We agree with the reviewer that there are certain losses during the work, but we have not considered that in this study.

 

22. Table 3 shows various parameters for the approximation of experimental data by the Langmuir and Freundlich equations. Are the authors sure that when using only 4 (or 5 if the point with zero amount of adsorbent was made) they can give the results of the approximation parameters with an accuracy of 6 significant digits? I believe that using only 4 experimental points without specifying a confidence interval is not enough to construct an adsorption isotherm and derive a statistically significant difference between the descriptions of the two theoretical models.

Response

 

The points are 5 (without zero point) for ABs adsorbents (Fig. 8). 

For ARs adsorbents the points are also 5 (without zero point) in Fig. 6 and Fig. 7. The correct Fig. 6 and Fig. 7.

 

 

 

Figure 6. The impact of initial concentration of oil on the percentage of oil onto (a) ABs and ARs (1g adsorbent, pH 6.5, Temp. 25 °C, 60 min).

 

Figure 7. Adsorption isotherm for removal of oil onto ARs adsorbent (1g ARs, pH 6.5, Temp.25℃, 60 min).

 

Figure 8. Adsorption isotherm for removal of oil onto ABs adsorbent (1g ABs, pH 6.5, Temp. 25℃, 60 min).

 

 

 

23. In lines 293-298, the authors describe the conditions of the experiment to determine the kinetic parameters of adsorption on the surface of AB and AR and do not talk about the shaking of the mixture mentioned earlier in line 112. How important is shaking and has it been used in studying adsorption kinetics?

 

Response

 

We thank the reviewer for this comment. In this study, the effect of contact time between the oil and the adsorbent was studied. The effect of shaking has not been studied. The shaking speed was at a constant moderate speed that has not been determined. The adsorption kinetics study measures the adsorption capacity of the adsorbent with time. The shaking speed is also important because the adsorption increase with increasing the shaking speed. However, we have not considered this in this study.

 

 

 

Conclusion

24. The phrase in the conclusion that the materials used are cheap may be correct, but does not follow from the results of the presented article.

Response

 

The following is added to the conclusion:

 

The experimental results demonstrated the ability of natural residues (ABs and ARs) to act as adsorbents in the treatment of oily water via adsorption. The use of natural waste as absorbent materials has both economic and environmental benefits due to the low cost of the adsorbent used and reduces environmental problems by converting it into useful materials. In this study, AB and ARs are new sorbent materials that were first used in oily water treatment. The ability of these adsorbents to remove oil from water was discovered to be affected by several factors, including adsorbent dosage, oil concentration, and contact time. The results showed that ABs could remove more oil from water than ARs, with removal capacities of 45 and 30 mg/g for ABs and ARs, respectively, and percentage removal of 94% and 70% for ABs and ARs, respectively. The study was expanded to include kinetic and adsorption models to better understand the adsorption mechanism. All of the experimental data for oil adsorption onto ABs and ARs adsorbents matched the Langmuir isotherm model well. The pseudo-second order kinetics model was used to describe the adsorption model. According to the pseudo-second-order kinetic model, the adsorption process is chemisorption, which involves a chemical reaction that occurs by the formation of covalent bonds through electronic sharing or exchange between oil molecules and the adsorbent's surface.

 

Despite the fact that in the present work the processes of oil adsorption important for practical application are studied, scientific conclusions about the correspondence of the Langmuir or Freundlich models may turn out to be statistically insignificant. The IR spectroscopy data require revision and more thorough analysis. Also, in discussing the results, it would be useful to compare the properties of the adsorbents studied in this study with other similar adsorbents of plant and animal origin. However, the idea of ​​the article is interesting and after setting up additional experiments and their more accurate processing, it can improve significantly.

Response

 

All the literature determines the fitting of the experimental isotherm data with isotherm models depending on the values of the correlation coefficient  (R²)  which from the plotting of the experimental data of each model. In our work, the values of R² in Freundlich isotherm were 0.9738 and 0.9797 for both ABs and ARs adsorbents. These results indicate good fitting with the Freundlich model, which suggests the formation multilayer of oil on the surface of the heterogeneous distribution of active sites on its surface. But the values of R² in the Langmuir model were 0.9983 and 0,9991, which are higher, indicating that the Langmuir model is better used to describe the adsorption data. To confirm our conclusion, the standard deviation MPSD was applied to our experimental data, and the results of MPSD confirmed that Langmuir is better at describing the adsorption process. According to the Langmuir model, the adsorption takes place by the formation monolayer of oil on the surface of the adsorbent that has a homogeneous distribution of active sites on its surface.

 

The important thing about IR in this measurement is to know the chemical functional group in the adsorbents.

 

Our work compares two adsorbents and studies the ability of these materials to remove oil. There are so many different natural materials and processes used to modify them that it is difficult to make comparisons.

 

We would really like to point out that, at this stage, we are not in the capacity to set up additional experiments because the materials used have run out, and it is challenging to re-prepare them because it takes a long time to collect and then prepare them for the experiment.

 

 

1. Katime, I.; Parada, L.; Meaurio, E.; Cesteros, L. Recent research developments in hydrogen bonding in polymer blends by Fourier transform infrared spectroscopy (FTIR) and calorimetry. Recent Res. Devel. Polym. Sci 1997, 1, 91-107.

 

Reviewer 2 Report

The authors studied the remediation of oily water by natural adsorbents. Effect of adsorbent dose, oil concentration, and time on the adsorption efficiency were studied. It is routine work. It can be published. However, some issues should be emphasized.

1. The novelty of this research should be inserted in the text clearly.

2. The stability and regeneration of the ABs and ARs should be presented in detail.

3. Page 10, lines 251-252, there is a careless error in the sentence “The R2 for Freundlich is slightly higher than Langmuir”.

4. Possible adsorption mechanism should be studied by some methods.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you very much for the recommendations. We request you to please kindly check the attached response to reviewers file.

Response to Reviewer 2

The authors studied the remediation of oily water by natural adsorbents. Effect of adsorbent dose, oil concentration, and time on the adsorption efficiency were studied. It is routine work. It can be published. However, some issues should be emphasized.

Comments and suggestion for authors:

We thank the reviewer for this kind decision on the possibility of publication. We would like to point out that the novelty of this research lies in the sorbent materials used and the modification and regeneration that is done on those adsorbents.

1. The novelty of this research should be inserted in the text clearly.

Response

We thank the reviewer for the suggestion. We have now incorporated the following in the introduction section:

The novelty of this research is that the two natural substances, animal bones (ABs) and anise residues (ARs), have not previously been used to remove oily pollutants from water. Furthermore, the research is beneficial from an environmental standpoint, as it reduces waste by converting these into useful substances.

 

2. The stability and regeneration of the ABs and ARs should be presented in detail.

Response

We thank the reviewer for this suggestion. Unfortunately, we have not studied the stability or regeneration of these two adsorbents in the present work. We will consider your suggestion in the future. In this work, our goal was to use this natural waste without processing or regeneration for the purposes of reducing process costs.

 

3. Page 10, lines 251-252, there is a careless error in the sentence “The R2 for Freundlich is slightly higher than Langmuir”.

 

Response

We thank the reviewer for pointing out the obvious error. We have now revised the line based on reviewer suggestions:

The R² for Langmuir is slightly higher than Freundlich, but the value of MPSD of the Langmuir model (3.2762) is lower than that of the Freundlich model (5.3534).

4. Possible adsorption mechanism should be studied by some methods.

 

Response

We thank the reviewer for this suggestion. We will study the adsorption mechanism in the future with the used adsorbents based on reviewers suggestions.

 

Author Response File: Author Response.docx

Reviewer 3 Report

The authors present a detailed comparison of the absorption of aqueous oil contaminants with crude oil using animal bones and anise residues. The strategy to use various organic matter for this purpose is not new, but these two sorbents appear not to be tested in the literature. The study looks at the absorption of oil on these materials; measurements of absorption based on temperature, time, and concentration; and the energetics and kinetics of absorption. The scope of the work is quite thorough. I support publication with minor revisions.

 

As a minor point, the text runs a little long in places. For example, the audience for this paper does not need to be convinced that FTIR is a valuable technique for the identification of organic functionalities. There are a variety of places in which the authors can make some assumptions about the audiences’ prior knowledge and curtail the text. That said, the choice of the 350 nm absorption for and whether and how that represents the distribution of functionalities that were identified in the IR experiments. The specific question I am asking is, I understand that 350 nm absorption provides a consistent measurement, but does it quantify all the materials that are being absorbed?   

 

My larger question was about the kinetics. The authors identify a second-order model, but there is no discussion about what that represents with respect to the absorption process. What are the ramifications of that on process? However, I am unsure if this is “pseudo” conditions. At runs with 50 mL of a 400 mg/L solution using 200 mg (or more) of sorbent, the sorbent appears to be in excess but only if we know that it has many sites or high capacity for absorption. It strikes me that oil concentrations would be unknown and it may be more useful for this application to consider excess oil and the effect of that on adsorption—or at least a justification as to why the reported scheme is a more informative.  

Author Response

Response to Reviewer 3

Reviewer 3

• The authors present a detailed comparison of the absorption of aqueous oil contaminants with crude oil using animal bones and anise residues. The strategy to use various organic matter for this purpose is not new, but these two sorbents appear not to be tested in the literature. The study looks at the absorption of oil on these materials; measurements of absorption based on temperature, time, and concentration; and the energetics and kinetics of absorption. The scope of the work is quite thorough. I support publication with minor revisions.

Response

We thank the reviewer for the kind words. We have now revised the manuscript based on your and other reviewers suggestions.

 

• As a minor point, the text runs a little long in places. For example, the audience for this paper does not need to be convinced that FTIR is a valuable technique for the identification of organic functionalities. There are a variety of places in which the authors can make some assumptions about the audiences’ prior knowledge and curtail the text. That said, the choice of the 350 nm absorption for and whether and how that represents the distribution of functionalities that were identified in the IR experiments. The specific question I am asking is, I understand that 350 nm absorption provides a consistent measurement, but does it quantify all the materials that are being absorbed?   

Response

We thank the reviewer for the comment. Please find the following as an explanation:

Spectrophotometry is a method of quantitative analysis to determine the concentration of chemical substances in solutions by measuring the intensity of the light absorbed by the chemicals when a beam of light passes through a sample solution. The basic principle is that each compound absorbs or transmits light over a certain range of wavelengths. We measure the wave experimentally as:

The absorption of sample solution of the light was measured at different wavelength. The adsorption is increase. Where the absorption increases with increasing wavelength until it reaches a certain value, then the absorption decreases with increasing wavelength. Then the wavelength that gives the highest absorption is taken.

After determining the wavelength of the given chemicals, an equilibrium curve is created, where standard samples of given chemicals are prepared with different specific concentrations, and the absorbance is measured for each concentration at the specified wavelength. Then the calibration curve is determined by plotting absorption versus concentration. This calibration curve is used to determine the concentration of the same chemicals of unknown concentration.

So, the chosen wavelength is specific to the oil used.

 

• My larger question was about the kinetics. The authors identify a second-order model, but there is no discussion about what that represents with respect to the absorption process. What are the ramifications of that on process? However, I am unsure if this is “pseudo” conditions. At runs with 50 mL of a 400 mg/L solution using 200 mg (or more) of sorbent, the sorbent appears to be in excess but only if we know that it has many sites or high capacity for absorption. It strikes me that oil concentrations would be unknown and it may be more useful for this application to consider excess oil and the effect of that on adsorption—or at least a justification as to why the reported scheme is a more informative.  

Response

We thank the reviewer for the comment provided. The following is added to the kinetic studies:

 

The experiments were carried out at 25 °C by adding 1g of adsorbents to six conical flasks of volume 100 ml each containing 50 ml of 400 mg/l oil-water mixture with a pH of 6.5. These six conical flasks, numbered 1,2,3,4,5,6, were subjected to different contact times of 5, 30, 60, 90, and 120 minutes. The adsorbent material is removed by separating funnel after each time interval, and the separated mixture is extracted with hexane and then analysed with an atomic absorption spectrophotometer. These steps were taken for both adsorbents.

 

The authors identify a second-order model, but there is no discussion about what that represents with respect to the absorption process

Table 5 shows the kinetics parameters and the linear correlation coefficient that were calculated and tabulated. The results show that the pseudo-second order kinetic model fits the experimental data very well, with R2 values of 0.9987 and 0.9992 for ABs and ARs, re-spectively, when compared to the pseudo-first order model. As a result, the oil removal adsorp-tion process using ABs and ARs adsorbents does not follow the pseudo-first order kinetics model, but rather the pseudo-second order kinetics model. According to the pseudo-second-order kinetic model, the adsorption process is chemisorption, which in-volves a chemical reaction that occurs by the formation of covalent bonds through electronic sharing or exchange between oil molecules and the adsorbent's surface. Adsorption of oil from oil-water mixtures using banana pseudostem fibres [31] and adsorption of oil onto powder and flake chitosan [35] yielded similar results.

[31] Husin, N.I.; Wahab, N.A.A.; Isa, N.; Boudville, R. Sorption Equilibrium and Kinetics of Oil from Aqueous Solution Using Banana Pseudostem Fibers. In Proceedings of 2011 International Conference on Environment and Industrial Innovation (ICEII 2011), Kuala Lumpur, Malaysia; pp. 177-182

[35] A.L. Ahmad, S. Sumathi, and B.H. Hameed, 2004, Chitosan: A Natural Biopolymer for  the Adsorption of Residue Oil from Oily Wastewater., Adsorptio science and Technology, Vol.22(1), pp.75-88

 

At runs with 50 mL of a 400 mg/L solution using 200 mg (or more) of sorbent, the sorbent appears to be in excess but only if we know that it has many sites or high capacity for absorption

1g not 0.2 g there is a typo. This experiment condition is the optimum condition after studied the effect of adsorbent dose, and concentration of oil. The optimum conditions were 1g adsorbent and 400 mg/l. at these conditions, the adsorption capacity was 45 and 30 mg/g for ABs and ARs, respectively.

Author Response File: Author Response.docx

Reviewer 4 Report

Current manuscript describes natural adsorbents named animal bones (ABs) and anise residues (ARs) for removal of oil from the water. After assessing the whole manuscript, some new information can be found. However, some questions should be addressed to improve the manuscript.
My opinions and comments about this manuscript are as follows:

1. The oil-water solution was used as simulated adsorption solution，It will be stratification, and the density of animal bones (ABs) and anise residues (ARs) significantly higher than the oil-water solution，How to ensure that the adsorbent is in full contact with the oil？

2. The adsorption process experiments involved adding 50ml of 400mg/l of the oil-water solution to a number of conical flasks containing a certain weight of the adsorbent (0.2-2g). In theory,The maximum saturated adsorption capacity are 100mg/g, 20mg/g,10mg/g,while the weight of the adsorbent are 0.2g,1.0g and 2.0g respectively.

3. There is only IR analysis in the paper.And they're depicted separately which Look out of order.Please redraw and put the samples before and after adsorption in one Figure, so that it is easier to find the difference.

4. Why the surface area and pore volume of the adsorbent was not determined? The surface area and pore volume are the key indictors reflecting the properties of adsorbent.

5. The hydrophobicity of the sample may change obviously before and after oil absorption，Please add the contact Angle test.

6. TGA test can determine the process of sample mass change with temperature，Therefor the adsorption of oil by ABs and ARs can be supplemented，Please add the TGA test.

7. If it is possible, please provide a comparative table to compare the efficacy of different synthesized natural adsorbents materials and your material to highlight the significance of this study.

8. In the third paragraph of introduction, some PEI loaded absorbent for the removal of metal ion should be cited, eg.: Materials 2022, 15, 6553 and Journal of Saudi Chemical Society 2021,25, 101299

9. In Figure 6，the ordinate is in the wrong unit.

10. Please use three-line table in the article.

11. Line 307-309 and Line 307-309, ‘the boundary conditions qt= 0 at t = 0 and qt= qt at time gives..’，The expression is not appropriate，Please refer to the literature for presentation.

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

 

Thank you very much for the recommendations. We request you to please kindly refer the attached response to reviewer.doc file. 

 

Response to Reviewer 4

 

Current manuscript describes natural adsorbents named animal bones (ABs) and anise residues (ARs) for removal of oil from the water. After assessing the whole manuscript, some new information can be found. However, some questions should be addressed to improve the manuscript.

 

Response

We thank the reviewer for the comments provided. We really appreciate your time and effort dedicated to our manuscript.

My opinions and comments about this manuscript are as follows:

 

1. The oil-water solution was used as simulated adsorption solution. It will be stratification, and the density of animal bones (ABs) and anise residues (ARs) significantly higher than the oil-water solution How to ensure that the adsorbent is in full contact with the oil？

 

Response

 

We thank the reviewer for this observation. We would like to point out that the reported density of these two adsorbents are near or little less than the density of water. So, the adsorbents were in full contact with oily water during our research.

 

Animal bones (ABs) used is a fish scales waste, and its density is 900 kg/m³ [1]

Anise residues (ARs) density is 966.35 kg/m³ [2]

 

1. C Balaji Ayyanar, K Marimuthu, B Gayathri, and Sankarrajan, 2020, Characterization and in vitro cytotoxicity evaluation of fish scale and seashell derived nano-hydroxyapatite high-density polyethylene composite, Polymers and Polymer Composites, Vol. 29(9) pp.1534–1542. DOI: 10.1177/0967391120981551.
2. K. Singh, M.K. Vishal, and R.K. Vishwakarma, 2015, Moisture Dependent Physical Properties of Anise Seeds, International Journal of Food Processing Technology, Vol 2, 39-45

 

 

2. The adsorption process experiments involved adding 50ml of 400mg/l of the oil-water solution to a number of conical flasks containing a certain weight of the adsorbent (0.2-2g). In theory, The maximum saturated adsorption capacity are 100mg/g, 20mg/g,10mg/g,while the weight of the adsorbent are 0.2g,1.0g and 2.0g respectively.

 

Response

We thank the reviewer for the observation. We would like to point out that based on our experimental conditions, the maximum adsorption capacity were 45, and 30 for ABs and ARs respectively which is evident in Fig.5.

 

 

 

 

3. There is only IR analysis in the paper. And they're depicted separately which Look out of order. Please redraw and put the samples before and after adsorption in one Figure, so that it is easier to find the difference.

 

Response

We thank the reviewer for the suggestion. However, even though the images are out of order, the results of before and after images depicting side by side would severely affect the readability of these images (see image below). As such, we opted to keep it as it is.

 

Figure 1. FTIR spectrum for ABs before and after adsorption of oil.

 

4. Why the surface area and pore volume of the adsorbent was not determined? The surface area and pore volume are the key indictors reflecting the properties of adsorbent.

 

Response

We thank the reviewer for this important comment. We would have liked to address the reviewer's concerns fully; however, the adsorbents were used up completely. As such, we could not address this here. We sincerely apologise for that. We will definitely do the suggested measurements in our future studies.

 

5. The hydrophobicity of the sample may change obviously before and after oil absorption，Please add the contact Angle test.

 

Response

We thank the reviewer for this important comment. We would have liked to address the reviewer's concerns fully; however, the adsorbents were used up completely. As such, we could not address this here. We sincerely apologise for that. We will definitely do the suggested measurements in our future studies.

 

6. TGA test can determine the process of sample mass changes with temperature，Therefor the adsorption of oil by ABs and ARs can be supplemented，Please add the TGA test.

 

Response

We thank the reviewer for this important comment. We would have liked to address the reviewer's concerns fully; however, the adsorbents were used up completely. As such, we could not address this here. We sincerely apologise for that. We will definitely do the suggested measurements in our future studies.

 

7. If it is possible, please provide a comparative table to compare the efficacy of different synthesized natural adsorbents materials and your material to highlight the significance of this study.

 

Response

 

We thank the reviewer for this important suggestion. We have now incorporated the following table based on the reviewers suggestions.

 

Table 3. Synthesised and natural adsorbents for oily water treatment

Adsorbent	Adsorbate	%Removal	qe (mg/g)	Ref
Textile fiber (TF)	Oil	95.2	4400	[1]
Walnut shells and Date pits	Oil	80 &87	-	[6]
Papyrus reed	Oil	94.5	229.726	[6]
Banana peel	Oil	97.45		[18]
Eggshell	Oil	100	108.69	[19]
Modified oil palm leaves (OPL)	Oil	-	1176	[21]
Sawdust	Oil	-	1282	[23]
Coconut coir	Oil	-	360	[23]
Anise residues	Oil	70	30	Present work
Animal bone	Oil	94	45	Present work

 

 

8. In the third paragraph of introduction, some PEI loaded absorbent for the removal of metal ion should be cited, eg.: Materials 2022, 15, 6553 and Journal of Saudi Chemical Society 2021,25, 101299

 

Response

We thank the review for the suggestion. However, none of the suggested studies is relevant to  our work i.e. Cost-effective Natural Adsorbents for Remediation of Oil Contaminated Water. As such these articles were not included in the revised manuscript.

 

 

 

9. In Figure 6 the ordinate is in the wrong unit.

 

Response

We thank the reviewer for this suggestion. We have now corrected the ordinate in the revised manuscript.

 

10. Please use three-line table in the article.

 

Response

We thank the reviewer for this suggestion. We have now implemented this in the revised manuscript.

 

 

11. Line 307-309 and Line 307-309, ‘the boundary conditions qt= 0 at t = 0 and qt= qt at time gives..’，The expression is not appropriate，Please refer to the literature for presentation.

 

Response

 

We thank the reviewer for the suggestion. We have now modified the text based on reviewer’s suggestion as follows:

 

The Lagergren pseudo-first-order model is described by the following equation:

                 (8)

 

where q_e (mg/g) and q_t (mg/g) are the sorption capacity at equilibrium and at time t, respectively, k₁ (1/min) is the rate constant of pseudo-first order. The integrating of Eq.8 and applying the boundary conditions q_t= 0 at t = 0 and q_t= q_t at t=t  gives the following linear equation:

       (9)

 

 

The pseudo-second order model is described by the following equation:

                  (10)

 

 

where k₂ (g/mg.min) is the rate constant of pseudo-second order. The integrating of Eq.10 and applying the boundary conditions q_t= 0 at t = 0 and q_t= q_t at time t=t gives the following linear equation:

                      (11)

 

In the present adsorption, kinetics data of adsorption of oil onto ABs and ARs were analysed using pseudo-first order (Eq. 9) and pseudo-second order (Eq. 11) models, as shown in Figs. 11 & 12, respectively.

 

 

Round 2

Reviewer 2 Report

I have reviewed this manuscript again. The authors answered some questions from reviewers. However, some important experiments, such as regeneration, adsorption mechanism, surface area etc., were not conducted. The absence of animal bones and anise residues should not become a proper reason. I think that animal bones and anise residues are easily found. I proposed that the authors resubmitted this manuscript in the future after completion some necessary experiments. I'll be glad to review it in the future.

Reviewer 4 Report

Although the author responded to the review comments,But most of the opinions were not substantially changed.The absence of samples should not be a reason for refusing to supplement conventional characterization.The quality of the articles did not improve significantly.