Biosorption of Cd(II), Co(II), and Cu(II) onto Microalgae under Acidic and Neutral Conditions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

     In this study, the author explores the adsorption capabilities of three species of microalgae for the heavy metals Cd, Co, and Cu under various conditions and employs the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models for analytical fitting. Additionally, it was observed that the adsorption process of these microalgae for heavy metals coincided with the production of Dissolved Organic Carbon. The research contributes positively to the utilization of bioremediation technologies for the elimination of heavy metal contamination in the environment. However, the paper has some shortcomings, including a lack of discussion on key results and deficiencies in the presentation of figures and tables. Issues such as incorrect numbering in figures and tables, and some formatting errors in the manuscript need further improvement. Major revision is imperative before publication. Some suggestions are listed below for consideration.

 

1.      The title should be concise and to the point; it is recommended that the author remove the specific names "(Chlorella vulgaris, Scenedesmus sp., and Spirulina platensis)" in title to maintain this conciseness.

2.      In the abstract section, the species names "onto three microalgae species (Chlorella vulgaris, Scenedesmus sp., and Spirulina platensis)" should be italicized to adhere to scientific naming conventions. Similarly, in the phrase "in the order S. platensis > C. vulgaris > Scenedesmus sp. while…", the species names should also be in italics. Similar to other places, the author should review and ensure the consistent italicization of species names throughout the document.

3.      In the Introduction, since heavy metals are a core focus of the paper, it is advisable for the author to provide a clear definition of heavy metals at the beginning of the introduction. Additionally, at the end of the first paragraph in the introduction, it is recommended that the author emphasize the harmful effects of heavy metals in the environment: “Although trace amounts of heavy metals naturally occur in soils, their excessive accumulation can deteriorate soil quality and harm surface plants.” The author should consider referencing two highly relevant review articles to enhance the background context and support the discussion [Biotechnology Advances, 72(2024)108337；Journal of cleaner production, 354(2022), 131681].

4.      At Line 60, when mentioning microorganism resources, the author should provide a brief introduction to microbial bioremediation techniques. Below is my attempt to revise this for clarity, which you can refer to. The recommended citations are also listed.

“…and even microorganisms like microalgae. Compared with traditional physical and chemical methods, microbial remediation is recognized as an effective and environmentally friendly approach. It offers several advantages including high efficiency, cost-effectiveness, and minimal environmental impact. This method has been successfully applied to the remediation of various pollutants, including heavy metals [Ecotoxicology and Environmental Safety, 254(2023) 114697；Bioresource Technology, 395 (2024), 130337]”

5.      Line 84, "mechanisms of Cd2+, Co2+, and Cu2+", please superscript.

6.      For Lines 96-97, where "BG 11" and "SOT" media are mentioned, it is essential to provide the full names and a detailed description of each component in these media.

7.      Section 2.6, "Biosorption Isotherm Models", suggests that the authors provide citation support for different fitting models.

8.      In Figure 1, the labels on the horizontal axis should not be "pH0" and "pH1 - pH0". The authors are advised to provide appropriate labels according to the meanings of the horizontal and vertical axes.

9.      In Figure 2, why are three different vertical axis labels set in each plot? It is recommended to use a single vertical axis label and plot the curves for the three types of bacteria based on their respective values.

10.   In Figure 2, what does "pH VS C.V." mean? Does it indicate the adsorption capacity of different bacteria at different pH values? Please clarify. Additionally, it is suggested to provide annotations for all three colored curves in each subplot (not just subplot a).

11.   In Section 3.2, "FTIR Spectra", the authors should not solely describe the meanings of select peak values. The focus should be on discussing and interpreting the experimental results, particularly the changes observed in the spectra before and after the adsorption of heavy metals by three different bacteria. The current content of this section lacks substantial significance.

12.   In Figure 3, displaying FTIR results, each of the three subplots should annotate representative peaks of functional groups within the graph.

13.   In Figure 4, the rationale behind choosing pH 4 needs clarification. The authors are urged to provide an explanation in the text of the article.

14.   Line 300 should refer to Figure 5 instead of Figure 1.

15.   Line 302 should reference Table 2 instead of Table 1.

16.   Line 319 should cite Table 3 instead of Table 1. The authors are advised to carefully verify the numbering of figures and tables throughout the article.

17.   In Figure 7 and Figure 11, the authors should present the standard deviation of the results.

18.   In the Conclusion section, the authors should not merely state the results. Instead, they should concisely summarize and emphasize the significance and value of the study. For instance, the implications and importance of the Dissolved Organic Carbon results should be thoroughly elucidated.

19.   There are several spelling, grammatical errors, issues with phrasing, and formatting errors throughout the document. It is recommended that the author carefully read through the entire manuscript to make corrections, preventing similar errors. Additionally, it is suggested to consider engaging a professional language service company to revise and proofread the English in the article.

Comments on the Quality of English Language

There are several spelling, grammatical errors, issues with phrasing, and formatting errors throughout the document. It is recommended that the author carefully read through the entire manuscript to make corrections, preventing similar errors. Additionally, it is suggested to consider engaging a professional language service company to revise and proofread the English in the article.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this paper, the biosorption of Cd, Co, and Cu ions onto three microalgae species was examined, and adsorption behavior in the equilibrium was examined through the three isotherm models in acidic and neutral conditions. All adsorption experiments were thoroughly done and the paper is well written. However, some minor issues should be addressed.

1. Abstract, line 21: the abbreviation DOC has to be defined before using it in the text. Therefore, in line 21:

… enhanced the production of DOC as a byproduct…., should be changed to

….. enhanced the production of dissolved organic carbon (DOC) as a byproduct…..

2. Introduction, line 84: Cd2+, Co2+, and Cu2+, put the ion charge to superscript

3. In part: 2.6. Biosorption isotherm models, give references for used isotherm equations. Also, check if Kelvin should be written in capital letter (line 170).

4. In Figure 2, the black line represents precipitation (%) of examined metal ions.

Also, in lines 230-205 it was written: Additionally, it was noted that at pH values above 9.5, 9.0, and 7.5, precipitation rather than adsorption became the predominant removal mechanisms for Cd, Co, and Cu, respectively.

However, according to the graphs, it seems that precipitation starts (the black line rises) at some lower values, pH 7.5 for Cd and Co, and at pH 5.5 for Cu, influencing the results obtained for adsorption.

5. Surface functional groups were analyzed using Fourier Transform Infrared Spectrometry, and this characterization method should be described in section 2. Materials and Methods.

6. Line 210: Stretches were observed between wavelengths....

FTIR spectra are given in Figure 3 as dependence between transmittance (%) and wavenumber, and wavelengths should be changed to wavenumber. Generally, FTIR spectra are shown with an x-axis ranging from 4000 to 400 cm^-1, maybe consider changing it in Figure 3.

9. In the part 3.2. FTIR spectra, line 209: Figure 3 shows the FTIR spectra of the biomass before and after metal adsorption. It should be mentioned if there is a difference between the FTIR spectra before and after adsorption and what that difference may indicate.

7. Line 300: in the figure caption change Figure 1 to Figure 5.

8. In order to have enough statistical representation, adsorption experiments should be done in triplicate, and the Figures representing the results of these experiments (Figures 2, 4-11) should have error bars.

 

9. Adsorption isotherm experiments were performed in neutral and acidic conditions. Specify the pH values (neutral pH 7 and acidic pH 4?) in part Materials and Methods.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The article has been revised thoroughly in accordance with the reviewers' suggestions and now meets the standards for publication.