Removal of Pharmaceuticals from Water by Tomato Waste as Novel Promising Biosorbent: Equilibrium, Kinetics, and Thermodynamics

Round 1

Reviewer 1 Report

Dear Authors and Editor,

In review, I received a manuscript draft entitled “Removal of pharmaceuticals from water by tomato waste as novel promising biosorbent: equilibrium, kinetics and thermo- dynamics” considered for publication in MDPI journal “Sustainability”. The manuscript explores the use of tomato industrial waste as a possible substitute for activated carbon for the removal of pharmaceuticals from waste waters. The manuscript is well composed, and below I listed few suggestions that can further improve the paper:

L113: Please insert the FTIR and SEM details (manufacturer, model, conditions used); including for the EDS detector. How were EDS samples prepared (coatings, drying, …)

L217: I am missing a short note on how the particle size was experimentally measured. From the text later on I can assume that from laser diffraction? In the text or image subtitle please include N (number of measured particles) with the Figure 1B; the particle size distribution assumes quite large number of measured particles to achieve certain standard on the mean (SN=S1/(sqrt(N), for S=1 we need about N=10.000 particles for SN=99%, then only N=100 for 90% “accuracy”). When correlating data with SEM observation, please note that particle distribution much differs from only rough estimation of the particle size and includes that “all” of the parties have to be measured on the SEM micrographs to avoid operator bias to focus more on “SEM-appropriate” particle sizes.

L235: As you specifically state the EDS results, please include the EDS analysis details – acc. voltage, how the quantification was obtained (semi-quant, standardless, ZAF, PRZ, …) etc.

Side-note: I would prefer the tomato TW would be sourced from industrial process side-product, but for a case-study the current experiment as a proof-of-concept the used would suffice.  

Good luck, Reviewer

Author Response

Dear Editor and Reviewer,

we thank you for your review. We have done our best to correct the article and meet all the requirements and questions this time. We are resubmitting the corrected manuscript as suggested by the reviewers. The added or changed text has been highlighted in yellow. Our responses are as follows:

 

 

Reviewer 1:

Dear Authors and Editor,

In review, I received a manuscript draft entitled “Removal of pharmaceuticals from water by tomato waste as novel promising biosorbent: equilibrium, kinetics and thermo- dynamics” considered for publication in MDPI journal “Sustainability”. The manuscript explores the use of tomato industrial waste as a possible substitute for activated carbon for the removal of pharmaceuticals from waste waters. The manuscript is well composed, and below I listed few suggestions that can further improve the paper:

Thank you.

L113: Please insert the FTIR and SEM details (manufacturer, model, conditions used); including for the EDS detector. How were EDS samples prepared (coatings, drying, …)

Details have been added, the preparation procedure has been explained (no additional drying was done prior to SEM and EDS analysis, but the sample was kept under dry conditions prior to analysis, and of course any surface water was removed by vacuuming the equipment chamber. The sample was previously coated with gold and palladium, but this was taken into account in the subsequent EDS analysis).

L217: I am missing a short note on how the particle size was experimentally measured. From the text later on I can assume that from laser diffraction? In the text or image subtitle please include N (number of measured particles) with the Figure 1B; the particle size distribution assumes quite large number of measured particles to achieve certain standard on the mean (SN=S1/(sqrt(N), for S=1 we need about N=10.000 particles for SN=99%, then only N=100 for 90% “accuracy”). When correlating data with SEM observation, please note that particle distribution much differs from only rough estimation of the particle size and includes that “all” of the parties have to be measured on the SEM micrographs to avoid operator bias to focus more on “SEM-appropriate” particle sizes.

The description of BET and particle size measurements have been added as requested. We thank the reviewer for his advice on how to improve the results and discussion; the Figure and discussion have been changed accordingly. The operator/sampling error in SEM was mentioned earlier. We have now added that SEM was not intended as a primary method for determining particle size and that the observation was not exhaustive/representative of the sample, but that the purpose of this method is to reveal morphological properties. We are aware that results obtained with different measurement methods and principles are hardly comparable and that PSD data differ and are difficult to relate to each other.

L235: As you specifically state the EDS results, please include the EDS analysis details – acc. voltage, how the quantification was obtained (semi-quant, standardless, ZAF, PRZ, …) etc.

We thank the reviewer for pointing this out. The analysis was semi-quantitative at best, as no standardisation was used and the output of the Tescan software was taken as given. We have therefore changed the precision of the potassium content to take this into account.

Side-note: I would prefer the tomato TW would be sourced from industrial process side-product, but for a case-study the current experiment as a proof-of-concept the used would suffice.  

If we do a scale-up study for this tomato TW, we will certainly obtain the material from an industrial process.

Good luck, Reviewer

Thank you.

Reviewer 2 Report

The manuscript presents interesting research results, however, they only contain a partial analysis of the sorbent, limited to five (to the best of my knowledge of rare drugs), disregarding other compounds that the new sorbent could potentially remove. I understand this is a case study, but it could be extended. Recycling waste has many advantages. However, they should also be examined for the sorption of other pollutants or refer to already performed works. The research results are presented in a very precise and legible way, which is undoubtedly another advantage of the work.

I would like to ask you about a few things:

1. Why were these pharmaceuticals selected for the research, even though they are not the most popular and most common in waters, such as paracetamol or ibuprofen? No justification was given, and this should be written after verses 91-93. It would be worth noting that these are agents often used in the treatment of animals (this is indicated by the source of the patterns), but are they present in significant amounts in the communal wastewater?
2. Have the authors considered what the sorption capacity of this material would be if all pharmaceuticals were used simultaneously?
3. The discussion of the results is very short and refers to the shortcomings in this type of research. How will the sorbent affect the concentration of phosphorus or nitrogen? The lack of reference of the obtained results to others does not allow for a full assessment of the quality of the new sorbent. It should be expanded, even comparing it with commonly and commercially used sorbents.

Author Response

Dear Editor and Reviewer,

we thank you for your review. We have done our best to correct the article and meet all the requirements and questions this time. We are resubmitting the corrected manuscript as suggested by the reviewers. The added or changed text has been highlighted in yellow. Our responses are as follows:

 

 

Reviewer 2:

The manuscript presents interesting research results, however, they only contain a partial analysis of the sorbent, limited to five (to the best of my knowledge of rare drugs), disregarding other compounds that the new sorbent could potentially remove. I understand this is a case study, but it could be extended. Recycling waste has many advantages. However, they should also be examined for the sorption of other pollutants or refer to already performed works. The research results are presented in a very precise and legible way, which is undoubtedly another advantage of the work.

Thank you.

I would like to ask you about a few things:

1. Why were these pharmaceuticals selected for the research, even though they are not the most popular and most common in waters, such as paracetamol or ibuprofen? No justification was given, and this should be written after verses 91-93. It would be worth noting that these are agents often used in the treatment of animals (this is indicated by the source of the patterns), but are they present in significant amounts in the communal wastewater?

The selected drugs belong to different therapeutic classes: Antibiotics (TYL), Anthelmintics (PRAZ and FEBA), Anesthetics (PROC) and Glucocorticoids (DEXA). These compounds were selected because of their extensive production and consumption worldwide, especially in veterinary medicine. Therefore, it is perhaps more appropriate to say that they are an environmental problem in municipal wastewater near, but not limited to, agricultural facilities.

1. Have the authors considered what the sorption capacity of this material would be if all pharmaceuticals were used simultaneously?

In this work, each pharmaceutical was tested individually to determine the sorption capacity of tomato-based sorbents as a function of the pharmaceuticals tested. If a mixture of pharmaceuticals were tested, the sorption capacity of each pharmaceutical tested in the mixture would likely be less than that determined individually because all pharmaceuticals would be competing for active sites on the sorbent at the same time, resulting in a deviation from the individually determined results in terms of the expected sorbed amount of a particular pharmaceutical. For a case study investigation, this approach seems valid, but for future studies we could investigate the mechanisms of simultaneous sorption for multiple drugs.

3. The discussion of the results is very short and refers to the shortcomings in this type of research. How will the sorbent affect the concentration of phosphorus or nitrogen? The lack of reference of the obtained results to others does not allow for a full assessment of the quality of the new sorbent. It should be expanded, even comparing it with commonly and commercially used sorbents.

First, we thank the reviewer for pointing out this problem. That being said, we need to limit our investigation to those areas where we can find something new. This investigation opens the idea of considering tomatoes for the removal of the selected pharmaceuticals in the form of a case study. I think our contribution to mitigate environmental problems is segmental, we cannot say that we can offer a comprehensive technological revolution. With regard to the decomposition of pharmaceuticals, the next step of investigation is to investigate whether there are decomposition products that may be more harmful than the parent chemicals. Only then is the issue of phosphorus and nitrogen relevant. Phosphorus and nitrogen concentrations are usually measured using methods that are not readily available to us. Even less are we provided with the techniques and expertise to put the effects of nitrogen and phosphorus concentrations in their proper context, namely the growth of algae and aquatic plants as a food source for fish and other organisms living in the water. With this in mind, we do not feel comfortable going too deep in this direction. Indeed, that would be an entirely new, stand-alone investigation. However, we have extended the discussion with the help of examples from the literature on the importance of such an overview (in relation to nitrogen and phosphorus).

Reviewer 3 Report

Overall quality and technical merit of the manuscript is good. Conclusions section needs strengthening, particularly addressing environmental sustainability aspects. See attached technical review.

Comments for author File: Comments.pdf

Author Response

Dear Editor and Reviewer,

we thank you for your review. We have done our best to correct the article and meet all the requirements and questions this time. We are resubmitting the corrected manuscript as suggested by the reviewers. The added or changed text has been highlighted in yellow. Our responses are as follows:

 

 

Reviewer 3:

The authors conducted a laboratory investigation using tomato wastes as a biosorbent for treatment of various pharmaceuticals including dexamethasone, procaine, praziquantel, tylosin, and febantel. The ability of the tomato waste to treat these aqueous pharmaceuticals was studied to determine equilibrium isotherms, kinetics, and thermodynamics involved. My comments addressing the technical and editorial of the revised paper are summarized below.

Thank you.

(1) p.10, par.2: The authors describe the correlation coefficients encountered in their isotherm models. So what? Significance? Implications?

High value (closer to 1) of the correlation coefficient (R²) mean that the applied isotherm could fitted well for the adsorption process. The low coefficient of the correlation coefficient (R²) indicates that the model is not representative of the data.

(2) p.14, par.1: The authors describe the correlation coefficients encountered in their isotherm models. So what? Significance? Implications?

High value (closer to 1) of the correlation coefficient (R²) mean that the applied kinetic model could fitted well for the kinetic process.

(3) Clarification is needed on the accuracy of various numbers cited in the text, as described below:

(a) p.3, par.1, line 3: …(75 mg/L)… [75 or 75.0]?

Thank you for correction, we have corrected in manuscript 75 mg/L in 75.0 mg/L.

(b) p.4, par.3, line 1: …contacting 1 gm TW… [1 or 1.0]?

Thank you for correction, we have corrected in manuscript 1 mg/L in 1.0 mg/L

(c) p.4, par.4, line 1: …in contact with 10 mL of… [10 or 10.0]? (d) p.16, par.3, line 2: …show that 1 g of TW can… [1 or 1.0]? 2

Thank you for correction, we have corrected in manuscript 10 mL in 10.0 mL

(4) p.4, Table 2: If possible, the authors should list the suspended solids concentration for the tomato waste.

Data is already provided in section 2.3. Batch adsorption experiments „1.0 g TW with 10.0 m)

(5) p.4, par.2: Were different multiple pharmaceuticals studied (rather than studies one at a time)?

No, only one at this time. In this work, each drug was tested individually to determine the sorption capacity of tomato-based sorbents as a function of the drugs tested. If a mixture of drugs were tested, the sorption capacity of each drug tested in the mixture would likely be less than that determined individually because all drugs would be competing for active sites on the sorbent at the same time, resulting in a deviation from the individually determined results in terms of the expected sorbed amount of a particular drug. For a case study, this approach seems valid, but for future studies we could investigate the mechanisms of simultaneous sorption for multiple drugs.

(6) p.4, Table 3: The authors should list the assumptions involved for the various adsorption isotherm models.

We have already described and explain it in the manuscript in section Results and discussion

(7) When continuing discussion of the meaning of various symbols used in equations, the discussion should not be indented; examples include:

(a) p.5, line 8

We have already described it in the manuscript “where qe and qt are the amounts of pharmaceutical (mg  g^- 1) adsorbed on TW (adsorbent) at equilibrium and at time t, respectively; k₁ (min^-1) is the rate constant of the pseudo-first order adsorption”.

(b) p.5, line 13 (c) p.5, line 21

We have already described it in the manuscript: „where k₂ is the rate constant of the pseudo-second order sorption (g mg^-1 min^-1)“. We have added in manuscript qe and qt are the amounts of pharmaceutical (mg  g^- 1) adsorbed on TW (adsorbent) at equilibrium and at time t, respectively.

(8) There are several editorial errors, in which the exponent is split between 2 lines of text; examples include:

(a) p.6, par.2, lines 3–4

Thank you for correction, we have corrected in manuscript.

(b) p.6, par.4, lines 1–2

Thank you for correction, we have corrected in manuscript.

(9) pp.16–17: The conclusions section should be strengthened. The authors need to emphasize the environmental sustainability aspects.

The section has been rewritten; I hope it is now appropriate.

Dried tomato waste was used in this case study as a novel sorbent for the removal of selected pharmaceuticals.

TW exhibits a complex chemical environment (in accordance with the characteristic lipid, phosphate, sugar, water, amide, etc. components), as confirmed by FTIR and EDS, and a morphology (polydisperse porous), as confirmed by SEM and nitrogen adsorption-desorption porosimetry. To determine the potential sorption capacity of TW, five different pharmaceuticals were selected at slightly higher concentrations than can be found in the environment. (50.0 g mL^-1) were selected and analysed individually using HPLC-DAD. The tomato wastes were chemically and microstructurally characterised before and after simulated sorption, indicating the stability of the sorbent.

We used the linear, Freundlich and Dubinin-Radushkevich (D-R) isotherms at different temperatures (298, 303 and 308 K) to describe the sorption experiment. The results indicate a spontaneous and physical nature of biosorption. The negative values of enthalpy change for biosorption of dexamethasone, procaine, praziquantel and tylosin at TW indicate exothermic processes, while the positive value for febantel indicates an endothermic process.

The kinetic data were analysed using: (i) kinetic models to determine the kinetic parameters (Lagergren's pseudo-first order and Ho's pseudo-second order) and (ii) adsorption-diffusion models to describe the transport mechanisms of drugs from aqueous solution to tomato waste as adsorbents (Weber-Morris intraparticle diffusion and Boyd film diffusion models).

The kinetic data of the studied pharmaceutical sorption on TW biosorbent were best fitted to the pseudo-second order kinetic model. The applied Weber-Morris intraparticle diffusion and Boyd film diffusion models showed that the mechanism of pharmaceutical sorption on the TW biosorbent is under the combined control of intraparticle diffusion (Weber-Morris) and film diffusion (Boyd).

This case study shows that TW must be considered as an effective biosorbent for drug removal. Nevertheless, it is necessary to further investigate its performance in terms of potentially harmful decomposition intermediates, as well as the influence on the presence of elements critical to aquatic systems, such as P and N.

(10) There are a number of minor editorial revisions that need to be corrected/revised. The spelling/grammatical errors include the following:

(a) p.1, Abstract, line 13: …pseudo-first and Ho’s pseudo-second) and… …pseudo-first order and Ho’s pseudo-second order) and…

Thank you for correction, we have corrected in manuscript (Lagergren’s pseudo-first and Ho’s pseudo-second)

(b) p.1, Introduction, par.1, line 9: …reach groundwater and drinking water [3]. …reach groundwaters and drinking waters [3].

Thank you for correction.

(c) p.1, Introduction, par.2, line 1: …emerged as the most promising option… …emerged as a promising option… 3

Thank you for correction.

(d) p.1, Introduction, par.2, line 3: …common adsorbents due to their effectiveness… …common adsorbent due to its effectiveness…

Thank you for correction.

(e) p.1, Introduction, par.2, line 3: activated carbons are not particularly… activated carbon is not particularly…

Thank you for correction.

(f) p.2, par.1, line 4: …phenols [8, 9] and pesticides [10], while… …phenols [8, 9], and pesticides [10], while…

Thank you for correction, we have corrected in manuscript.

(g) p.2, par.2, line 11: environmentally-friendly and cost-effective… environmentally-friendly, and cost-effective…

Thank you for correction.

(h) p.2, par.2, line 12: dyes, cations and other chemical… dyes, cations, and other chemical…

Thank you for correction, we have corrected in manuscript.

(i) p.2, par.3, line 4: …use. Tomato peel is usually …use. Tomato peels are usually

Thank you for correction.

(j) p.2, par.3, lines 9–10: …found to be good adsorbent for… …found to be a good adsorbent for…

Thank you for correction.

(k) p.4, par.1: Why is different line spacing used?

Thank you for correction, we have corrected in manuscript.

(l) p.5, par.1, line 4: …kinetics depends on the interactions… …kinetics depend on the interactions…

Thank you for correction.

(m) p.6, par.1, line 4: …stretching, i.e. asymmetric and symmetric… …stretching, i.e., asymmetric and symmetric…

Thank you for correction.(n) p.6, par.5, line 2: …water, amide etc.), i.e. with the chemical… …water, amide, etc.), i.e., with the chemical…

Thank you for correction.

(o) p.9, par.1, line 1: The authors indicated they employed pharmaceutical concentrations higher than what is typically encountered. Why? Provide the rationale/justification to use these higher concentrations.

We thank the reviewer for this comment. We have included an explanation in the paper.
The concentration range chosen (5.0 - 75.0 mgL^-1) is consistent with the literature, although many authors use a much higher concentration range to determine sorption coefficients (5.0 - 500 mgL^-1), depending on the instrumentation available to analyse the remaining pharmaceuticals after sorption. The sorption correlation with concentration is the same regardless of the concentration range, although unrealistically high concentrations should be avoided.

(p) pp.9–10, Figure 5: List the entire figure on a single page.

Thank you for correction.

(q) p.11, Table 4: I suggest listing the correlation coefficients for each isotherm model studied.

Thank you for correction.

(r) pp.12–13, Table 5: List the entire table on a single page.

Thank you for correction.

(s) p.13, Figure 6e: The x-axis label should be centered.

Thank you for correction.

(t) p.14, Table 6 heading: Why is different line spacing used?

Thank you for correction.

(u) p.15, par.1: Why is different line spacing used?

Thank you for correction.

(11) There are several grammatical/formatting issues related to the reference citations on pages 17–20: (a) Be consistent in the citing of article titles; only capitalize the first word of the article, or capitalize all important words.

Thank you for correction; we followed the instructions for authors for the preparing.

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In summary, the authors have drafted a good technical paper that reads pretty well. The authors need to address the review comments and suggested revisions contained in this review. The Conclusions section needs to be strengthened addressing environmental sustainability aspects. The paper, in its current form, is recommended to be declined. However, after these revisions are made and address the comments and concerns, the paper is then deemed suitable for publication in Sustainability.

Thank you, we followed recommendations and have rewritten the conclusions.

Round 2

Reviewer 2 Report

Dear Authors,
Thank you very much for the answers and corrections. I believe that the article in this corrected form can be recommended for publication. Congratulations, good job!