Beyond Bioremediation: The Untapped Potential of Microalgae in Wastewater Treatment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Overall, the manuscript sheds light on the potential of microalgae beyond the bioremediation, emphasizing the applications of algae biomass after the bioremediation.  The abstract and conclusion is very well written.  However, there is room for improvement in content as listed below.  

1.     All tables can be improved by adding horizontal line in the table to separate the items clearly and more organized

2.     Table 1 – would be good to add the present of microplastics/nanoplastic in WW

3.     Contents of ‘2.1 Wastewater treatment’ are too lengthy and technical.  This section solely explains the theory of wastewater treatment and does not contain any review components.  Please shorten the section and citations are required. 

4.     Line155 – Please rephrase ‘EPs are gaining attention thanks to their…..” Suggest not to use ‘thanks’ in review paper

5.     Table 2 is not necessary, and it can be included as supplementary materials

6.     Line 225 - Global issues today include reducing climate change, sustainable use of natural resources, and decreasing the pollution of the environment --- This sentence is not right as those are not global issues but challenges.  Please correct the sentence.

7.     Line 226 - According to estimates ---- estimates of what? Please state clearly

8.     Line 228 – 233 – Citations are needed

9.     Section 4.1 – Suggest dividing the bioconversion and bioadsorption into 2 separate sections.  Authors are using a very general term of microalgae which is not convincing as content for review paper.  Hence, please add examples of microalgae in the content with citations.

10. Figure 1 is confusing as lack of explanation.  Additionally, Figure 1 was not mentioned in any paragraph of the paper.

11. Line 279-283 – citation is needed

12. Line 279-283 – The authors mentioned that the efficiency of the algal bioremediation is influenced by a range of physicochemical factors including pH, redox potential, temperature, duration and strength of light exposure, hydraulic retention time, size of adsorbents, and concentration of environmental pollutants, however not all above factors are discussed in the following section (4.1.1 and 4.1.2).   Would be good to include the discussion for all factors above in the next section.

13. There is no flow from the previous sections to section 4.2.  A new term of micro-pollutant is used in this section while other sections are using pollutants.  Please standardize the use of term. 

14. ‘Main find’ is not a suitable title for this section.  Please rename.

15. Line 347-348 – Please restructure the sentence.  It is too lengthy to understand.

 

Comments on the Quality of English Language

Some sections are very well written English.  However, improvement is needed for few sections, e.g. section 4.2

Author Response

Overall, the manuscript sheds light on the potential of microalgae beyond the bioremediation, emphasizing the applications of algae biomass after the bioremediation. The abstract and conclusion is very well written.

We would like to thank the reviewer’s comment and appraisal.

However, there is room for improvement in content as listed below.

1. All tables can be improved by adding horizontal line in the table to separate the items clearly and more organized.

The suggestion has been accepted and tables were modified according to the reviewer’s suggestion.

2. Table 1 – would be good to add the present of microplastics/nanoplastic in WW.

We thank the reviewer for the suggestion; indeed, it would be an interesting addition, and we considered it initially, but we felt that the micro- and nano-plastics would merit a review on its own (more than 17,000 papers published since 2020; Google Scholar).

3. Contents of ‘2.1 Wastewater treatment’ are too lengthy and technical. This section solely explains the theory of wastewater treatment and does not contain any review components. Please shorten the section and citations are required. 

The suggestion has been accepted and the section was shortened leaving the essential parts of the treatment and effect on pollutants removal. The references number 75, 76, 77, 78, 79 were added accordingly.

4. Line 155 – Please rephrase ‘EPs are gaining attention thanks to their…..” Suggest not to use ‘thanks’ in review paper

We thank the Reviewer for the suggestion and the text was changed accordingly.

5. Table 2 is not necessary, and it can be included as supplementary materials

We thank the reviewer for the suggestion; Table 2 was moved to supplementary material.

6. Line 225 - Global issues today include reducing climate change, sustainable use of natural resources, and decreasing the pollution of the environment --- This sentence is not right as those are not global issues but challenges. Please correct the sentence.

Thank you for the suggestion; the text was changed accordingly.

7. Line 226 - According to estimates ---- estimates of what? Please state clearly

Considering the reviewer’s comment, the sentence was rephrased and now reads: “Global food, water, and energy demand is predicted to increase by 60%, 80%, and 50%, respectively, between 2000 and 2050 [93,94].” (line 220).

8. Line 228 – 233 – Citations are needed

Thank you for the comment, references number 95 and 96 were added. (new line 225)

9. Section 4.1 – Suggest dividing the bioconversion and bioadsorption into 2 separate sections. Authors are using a very general term of microalgae which is not convincing as content for review paper. Hence, please add examples of microalgae in the content with citations.

 

We agreed with the reviewer’s suggestion, and we divided the paragraph in subtitles for each mechanism of action carried out by microalgae, adding examples to each of them. Reference number 109 was added.

10. Figure 1 is confusing as lack of explanation. Additionally, Figure 1 was not mentioned in any paragraph of the paper.

Following the reviewer’s comment, Figure 1 was improved. However, the authors have decided that it make more sense to use it as a Graphical abstract of the manuscript as it is a more general picture explaining the concept of the paper.

11. Line 279-283 – citation is needed

References number 126 an d127 were added. (new line 342)

12. Line 279-283 – The authors mentioned that the efficiency of the algal bioremediation is influenced by a range of physicochemical factors including pH, redox potential, temperature, duration and strength of light exposure, hydraulic retention time, size of adsorbents, and concentration of environmental pollutants, however not all above factors are discussed in the following section (4.1.1 and 4.1.2). Would be good to include the discussion for all factors above in the next section.

Following the Reviewer’s suggestion the discussion was enlarged, and further sections were added.

13. There is no flow from the previous sections to section 4.2. A new term of micro-pollutant is used in this section while other sections are using pollutants. Please standardize the use of term. 

We thank the Reviewer for the suggestion, but we don’t think there is a lack of flow from section 4.1 to 4.2. The former section describes the mechanisms of action of microalgae in bioremediation and the following section shows different applications of the mechanisms described previously. Since is not clear yet which mechanism is carried out in every case, we preferred not to mention them in the table. Regarding the use of “term”, the text was revised thoroughly.

14. ‘Main find’ is not a suitable title for this section. Please rename.

Thank you for the suggestion and the title of this section was changed to a more suitable one.

15. Line 347-348 – Please restructure the sentence. It is too lengthy to understand.

Following the Reviewer’s suggestion, the sentence now reads:” Daneshvar’s research team also studied the removal of nutrients from municipal wastewater using Tetraselmis suecica and Scenedesmus quadricauda. The results showed that S. quadricauda outperformed T. suecica, achieving removal efficiencies of 95.3% for nitrates and 89.8% for phosphates [151].” (new line 446-449)

Comments on the Quality of English Language.

Some sections are very well written English.  However, improvement is needed for few sections, e.g. section 4.2.

The English was extensively reviewed and when needed changes were made.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Reviewing report

Review entitled " Beyond bioremediation: the Untapped Potential of Microalgae in Wastewater Treatment"

Good work but still need more additions.  I tried to help by suggesting some references but you still need to make your own search.

1. Please, capitalise the first letter for each keyword: Bioremediation; Wastewater treatment, etc.

2. You need to talk about the conventional methods of water treatment in the introduction section. Then talk about some examples of microalgae species which used in bioremediation. Briefly.

I knew you talked after as a subtitle but you still need to talk in the introduction as a briefly.

3. Please, justify the words inside table 1 and make them centered in the middle. The same table 2.

4. You need to define what I the COD, BOD, etc.

5. Please remove the extra spaces on page 7.

6. Where are the references at line 184, 193, 202

In addition, please make the links as a reference number. For example link on page 8.

7. On table 2, please make the abbreviation for metal with there charge number “+ or -”. For example Cr⁺⁶ is toxic while Cr⁺³ nontoxic.

8.  Please remove the bold style from the caption of figure 1 “Traditional versus the innovative approach on wastewater treatment using 285 microalgae for the removal of inorganic and organic pollutants.”

The same table 1 & 2 captions.

9. You need to talk about pH as a subtitle under “4.1 How do microalgae work?” by details.

10. On table 3, the words inside need to be justified.

11.  Under this title "4.1 How do microalgae work?"  you talked about subtitles  "such as pH, Temperature, adsorbent dose" but you still need more subtitle talk about the effect of :

- Biological Factors

• Algal species: different algal species exhibit varying capacities for pollutant uptake and degradation.
• Algal growth phase: the growth stage of the algae can impact its bioremediation potential.
• Presence of other microorganisms: the interaction with other microorganisms (bacteria, fungi) can affect algal performance.

- Nutrient Availability

• Nutrient composition: the availability of essential nutrients like nitrogen, phosphorus, and micronutrients can impact algal growth and bioremediation.
• Nutrient limitation: insufficient nutrients can hinder algal growth and pollutant removal.

- Environmental Factors

• Salinity: salinity levels can affect algal growth and pollutant removal.
• Presence of inhibitors: the presence of toxic substances can inhibit algal activity.

Please make your search and write more effects with more subtitles about this. I just help but you still need make your search.

12. You need to add a title about “Bioremediation mechanisms” with subtitles for the type such as : biosorption, bioaccumulation, etc.

For help see this : Abdelfattah, A., Ali, S. S., Ramadan, H., El-Aswar, E. I., Eltawab, R., Ho, S. H., ... & Sun, J. (2023). Microalgae-based wastewater treatment: Mechanisms, challenges, recent advances, and future prospects. Environmental science and ecotechnology, 13, 100205.‏

But you still need to make your own search.

13. You need to talk about the advantages and disadvantage of microalgae.

See this: Ahmad, I., Abdullah, N., Koji, I., Yuzir, A., & Mohamad, S. E. (2021). Potential of microalgae in bioremediation of wastewater. Bulletin of Chemical Reaction Engineering & Catalysis, 16(2), 413-429.‏

There are somepoint here inside this reference you didn’t talk about in your subtitles : drawbacks and main findings.

In addition, my advice you can make a title “main findings” then make a subtitle for “advantages” and change the subtitle name “drawbacks” to the new name “disadvantages”.

14. Where is the final title “conclusion”. You need to make section about that in the end of the review.

 

 GOOD LUCK

Author Response

Good work but still need more additions.  I tried to help by suggesting some references but you still need to make your own search.

We thank the reviewer for his/her kind help.

1. Please, capitalise the first letter for each keyword: Bioremediation; Wastewater treatment, etc.

Thank you for your suggestion, corrections were made accordingly.

 

2. You need to talk about the conventional methods of water treatment in the introduction section. Then talk about some examples of microalgae species which used in bioremediation. Briefly.

I knew you talked after as a subtitle but you still need to talk in the introduction as a briefly.

 We thank the Reviewer for the suggestion and the text was modified (line 62) accordingly, to complete the introduction section.

 

3. Please, justify the words inside table 1 and make them centered in the middle. The same table 2.

Thank you for the comment, all the tables were changed to make them easier to read and follow.

 

4. You need to define what I the COD, BOD, etc.

All the abbreviations were double checked throughout the text.

 

5. Please remove the extra spaces on page 7.

The extra spaces were removed, as suggested.

 

6. Where are the references at line 184, 193, 202

In addition, please make the links as a reference number. For example link on page 8.

We thank the reviewer for the comment, the links were substituted by references to the appropriate legislation (references 88 and 90).

 

7. On table 2, please make the abbreviation for metal with there charge number “+ or -”. For example Cr+6 is toxic while Cr+3 nontoxic.

Following the suggestion of another reviewer, Table 2 was moved to Supplementary Material. Nonetheless, the text was changed as suggested.

 

8. Please remove the bold style from the caption of figure 1 “Traditional versus the innovative approach on wastewater treatment using 285 microalgae for the removal of inorganic and organic pollutants.”

The same table 1 & 2 captions.

The Bold format was removed as suggested. Figure 1 was removed from the body of the manuscript and is now suggested as a Graphical Abstract.

 

9. You need to talk about pH as a subtitle under “4.1 How do microalgae work?” by details.

We thank the Reviewer for the comment, however, there is a sub-section, namely 4.1.1, in which the overall effect of pH on microalgae-based bioremediation is explained. Since the focus of the review is showing the actual progresses and the lack of studies in the field, we consider that detailing each aspect and mechanism of the bioremediation would be too lengthy and unessential.

 

10. On table 3, the words inside need to be justified.

We thank the Reviewer for the suggestion, and we’ve modified the text accordingly.

 

11. Under this title "4.1 How do microalgae work?" you talked about subtitles  "such as pH, Temperature, adsorbent dose" but you still need more subtitle talk about the effect of :

- Biological Factors

• Algal species: different algal species exhibit varying capacities for pollutant uptake and degradation.
• Algal growth phase: the growth stage of the algae can impact its bioremediation potential.
• Presence of other microorganisms: the interaction with other microorganisms (bacteria, fungi) can affect algal performance.

- Nutrient Availability

• Nutrient composition: the availability of essential nutrients like nitrogen, phosphorus, and micronutrients can impact algal growth and bioremediation.
• Nutrient limitation: insufficient nutrients can hinder algal growth and pollutant removal.

- Environmental Factors

• Salinity: salinity levels can affect algal growth and pollutant removal.
• Presence of inhibitors: the presence of toxic substances can inhibit algal activity.

Please make your search and write more effects with more subtitles about this. I just help but you still need make your search.

We thank the Reviewer for the suggestions. The research was expanded, and a new section (4.1.3 Light exposure and redox potential) was added, as well as new references [142, 143, 144, 145, 146, 147]. We hope that the details included are deep enough and meet the reviewer’s requirement.

 

12. You need to add a title about “Bioremediation mechanisms” with subtitles for the type such as : biosorption, bioaccumulation, etc.

For help see this : Abdelfattah, A., Ali, S. S., Ramadan, H., El-Aswar, E. I., Eltawab, R., Ho, S. H., ... & Sun, J. (2023). Microalgae-based wastewater treatment: Mechanisms, challenges, recent advances, and future prospects. Environmental science and ecotechnology, 13, 100205.‏

But you still need to make your own search.

Thank you for the comment. As suggested, we’ve added different subsections for each mechanism of action of the microalgae. The following references were added as well: [101-122]

 

13. You need to talk about the advantages and disadvantage of microalgae.

See this: Ahmad, I., Abdullah, N., Koji, I., Yuzir, A., & Mohamad, S. E. (2021). Potential of microalgae in bioremediation of wastewater. Bulletin of Chemical Reaction Engineering & Catalysis, 16(2), 413-429.‏

There are somepoint here inside this reference you didn’t talk about in your subtitles : drawbacks and main findings.

In addition, my advice you can make a title “main findings” then make a subtitle for “advantages” and change the subtitle name “drawbacks” to the new name “disadvantages”.

We thank the Reviewer for the comment; however, we explained the advantages of the microalgae within the paragraph “biomass utilization” and the disadvantages within the paragraph “drawbacks”. Our aim in the manuscript was to explain first the worst side of microalgae and then finding a solution to the problem.

 

14. Where is the final title “conclusion”. You need to make section about that in the end of the review.

Thank you for the comment, however, in our review, the conclusions paragraph is named “Final considerations”, which, in our opinion, conveys the same meaning.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear resecetd author, 

Thank you for your corrections and and additions. There are still small things missed: (deleted compared to the previous manuscript version). You need to back it.

1. You removed figure 1. Where figure 1. I just asked to make the caption non-bold. I know its may deleted by mistake. 

2. There are extra spaces between lines. For example: 235-236, 238-240,  etc. Please revise the whole manuscript.

3. Where is the talkin about conventional methods on introduction part ?

4. You said "here is a sub-section, namely 4.1.1, " Where? 

Please reread and see if there s pH part or not. 

Please talk about pH.

5. Where is table 3 ? I asked about justification not deleting. Please correct it as I asked in the previous report and add it. 

You said that "We thank the Reviewer for the suggestion, and we’ve modified the text accordingly. "

Thank you. But you still to back the table . Its important.

GOOD LUCK 

Author Response

Reviewer 2

 Dear resecetd author, 

Thank you for your corrections and and additions. There are still small things missed: (deleted compared to the previous manuscript version). You need to back it.

 We thank the reviewer for the further comments and appraisal. We kindly apologize if we did not fulfill all the requests during the first round of comments.

 

1. You removed figure 1. Where figure 1. I just asked to make the caption non-bold. I know its may deleted by mistake. 

 Figure 1 was improved considering the comments made by the reviewer. However, given its general context we thought it would make more sense to use it as a graphical abstract. Hence, the Figure and references to it were removed from the text and the figure was uploaded as a graphical abstract during the submission of the revised manuscript. However, we can consider keeping it as Figure 1 in the body of the paper if the Reviewer feels that it is important.

 

2. There are extra spaces between lines. For example: 235-236, 238-240,  etc. Please revise the whole manuscript.

 We thank the reviewer for the observation; it was difficult to keep track of all the changes in the marked version of the manuscript. We revised the text thoroughly and deleted the extra spaces.

 

3. Where is the talkin about conventional methods on introduction part ?

 Following the reviewer’s suggestion we have briefly described conventional wastewater treatment methods (L44-47). We do not wish to detail it too much in the introduction because it is already detailed in chapter 2.

 

4. You said "here is a sub-section, namely 4.1.1, " Where? 

Please reread and see if there s pH part or not. 

Please talk about pH.

 We kindly apologize; there was a mistake in the numbering of the sub-paragraphs. Section 4 has a sub-section dedicated to “Temperature, pH and hydraulic retention time” (section 4.1.4) and the effect of pH is discussed in L356-365.

 

5. Where is table 3 ? I asked about justification not deleting. Please correct it as I asked in the previous report and add it. 

You said that "We thank the Reviewer for the suggestion, and we’ve modified the text accordingly. "

There were conflicting recommendations from the 2 reviewers on the first revision round. Reviewer 1 recommended to move Table 2 to Supplemental Material, with which we agreed, since the table was too lengthy, breaking the rhythm of the reading. This table (now Table S1) is referred to in the body manuscript in line 208. Due to this change, the actual Table 2 is the previous Table 3.

Thank you. But you still to back the table . Its important.

GOOD LUCK 

We hope these explanations and modifications fulfill the reviewer’s recommendations.