Performance of Continuous Electrocoagulation Processes (CEPs) as an Efficient Approach for the Treatment of Industrial Organic Pollutants: A Comprehensive Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The review is well organized. I propose to accept the article after minor revision. In Fig. 11, please present data starting from 2003 to 2025. In the calculations, please use mathematical formulas (do not use the letter X for multiplication). Please provide examples of removal of selected organic compounds (not only COD).

Author Response

Responses to the Reviewers

 

Dear Editor

We highly appreciate your efforts in leading this esteemed high quality and recognized journal. We would like also to thank the five reviewers who have given deep intention and provide us with constructive comments. Actually, we considered all of their comments in preparing our revised manuscript, and we find that it is significantly improved to fulfill the journals scientific and editorial requirements. We hope that you will find that it is now suitable for publication.     

Responses to Reviewer 1

The authors highly appreciate the reviewer important comments. We actually divided them into three comments to the suitable response for each one of them as in the following:  

Comment 1: The review is well organized. I propose to accept the article after minor revision. In Fig. 11, please present data starting from 2003 to 2025.

Response 1: Thank you for the comment. Figure 11 already presents data covering the period from 2003 to 2025, as stated in the figure caption. To enhance clarity, we have revised the caption to explicitly mention the time range, data source (Scopus), search query, and retrieval date. The updated caption is highlighted in yellow in the revised manuscript for easy reference.

Comment 2: In the calculations, please use mathematical formulas (do not use the letter X for multiplication).

Response 2: Corrected. All instances of the letter "X" used for multiplication have been replaced with the proper multiplication symbol (×), using the Equation function in Microsoft Word. Additionally, all formulas have been reformatted to follow standard mathematical notation and formatting conventions.

Comment 3: Please provide examples of removal of selected organic compounds (not only COD).

Response 3: Thank you for your important comment. While COD is a widely reported aggregate parameter, we would like to clarify that the manuscript already includes a broad range of examples related to the removal of various organic and associated pollutants. In addition to COD, Tables 1 and 2, along with the corresponding discussions, provide data on the removal of color, turbidity, total organic carbon (TOC), biochemical oxygen demand (BOD), humic substances, total suspended solids (TSS), total dissolved solids (TDS), total nitrogen (TN), phenols, and microbial indicators such as E. coli and fecal coliforms.

To further emphasizing this point, we have added a new paragraph at the end of the introduction to highlight the diversity of organic pollutants addressed throughout the review. Additionally, these examples have been highlighted in yellow color in the revised manuscript for your convenience.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Comment 1:  

A thorough revision of Section 2.1 is recommended due to the presence of multiple misplaced commas (e.g., [31], ,k, ,n,….) which affect the readability of the text. Furthermore, key experimental details are lacking, including the nature of the organic effluent, the applied current density, the pH, the supporting electrolyte concentration, flow rate, reaction time, the type of electrodes employed and pollutant removal efficiency.

Comment 2:

For improved clarity and scientific rigor (Section 2.1), it is recommended to expand on the interpretation of the obtained results, as this would help readers better understand the significance and implications of the findings.

Comment 3:

It is recommended that the manuscript be carefully reviewed for consistency in the expression of units. The use of standardized scientific notation (e.g., mg·L^-1, g·L^-1, L·h^-1, $·m^-3…) should be applied uniformly throughout the text.

Comment 4:

The manuscript includes several abbreviations (e.g., COD, HRT, SEEC, TOC, DBO₅, R²…) that are not defined when first introduced. For clarity and readability, all abbreviations should be clearly defined upon their first occurrence.

Comment 5:

In Section 2.1, the sentence regarding Moussavi et al. mentions that “the reaction constant increased with aeration, from 477 to 78 mL·g⁻¹·min⁻¹.”  However, the numerical values suggest a decrease rather than an increase. This inconsistency should be reviewed and corrected accordingly.

Comment 6:

At the end of page 5, the phrase “During the past 25 years” should be corrected to “During the last 25 years” for proper usage in this context.

Comment 7:

The citation format should be revised. The sequence “[2, 3, 28, 31–37] [38–47] [48–57] [58–61]” is incorrect and should be merged or reformatted appropriately.

Comment 8:

Reference [61] is incorrectly attributed to Kumar et al.; it should be Purkait et al. This should be corrected.

Comment 9:

The highlighted passage beginning with “Fe rods… Response surface….”  needs to be reviewed and revised for clarity, accuracy, and proper sentence structure.

Comment 10:

The expression 'using new Fe' in the context of Mehralian et al. (page 6) is ambiguous. Please clarify whether this refers to freshly introduced iron, a particular form or phase of iron, or another specific meaning.

Comment 11:

Table 1 should be carefully revised. The unit notations are not uniform throughout the table, and several abbreviations are used without being defined (e.g., WW, N°, TPH, TSS, MPP, BPS, NTU, MPS…). Additionally, the font style is inconsistent across different entries. It is also recommended to include the reaction time, as it is an important operational parameter for evaluating and comparing the treatment efficiency, and the table title “Table 1: Summery of main..” contains a spelling error “Summery” should be corrected to “Summary.”

Comment 12:

On page 12,

• the author name Mois´es et al.” contains a typographical error and should be corrected to Moisés et al.
• Gunawan et al. is cited as reference [69], but it corresponds to [70].
• Dan et al. is cited as [73], but the correct reference is [74].
• For Ghernaout et al., the citation should be simply [63] the year 2010 should be removed.

Comment 13:

The final paragraph on page 12 should be revised for clarity. The sentence mentioning Bani-Melhem et al., Makwana and Ahammed, Jiménez et al., Gil-Pavas et al., and Gunawan et al., along with various types of treated wastewater, lacks the use of the word “respectively”. This omission makes the associations between each study and the corresponding wastewater type unclear. It is recommended to correct this for better readability and accuracy.

Comment 14:

A revision of Table 2 is recommended. The title currently states 'since 20 years', yet the earliest reference listed is from 2010, which suggests 'since 15 years' would be more accurate. Additionally, unit formatting throughout the table should be reviewed and harmonized to ensure consistency and adherence to standard scientific notation. It is also important to define all abbreviations used in the table, such as ES, SBBR, UASB, etc., to ensure clarity and accessibility for all readers, and the table title “Table 2: Summery of main..” contains a spelling error “Summery” should be corrected to “Summary.”

Comment 15:

In Section 3.1.1 (page 16), the abbreviation “TSS” appears without prior definition. It is important to define all abbreviations at first use for instance, Also, the author name “Maheshet al.” in the last paragraph contains a typographical error and should be corrected to “Mahesh et al.”

Comment 16:

In Equation (1), the symbols F, I, and Δt are not defined in the text. These should be properly introduced to ensure clarity for the reader. Additionally, the term ET should be defined.

Comment 17:

The section numbering appears to be incorrect. "3.1.1. Combined processes" should be labeled as "3.1.2"

Comment 18:

The citation "Gunawan et al., [7]" should be corrected to "Gunawan et al., [70]" to ensure consistency with the reference list.

 

Comment 19:

In Equation (3), the term C should be replaced with C_t to accurately reflect the concentration at time t. Additionally, the relevance of reference [90] to the preceding sentence is unclear and should be reconsidered.

Comment 20:

The manuscript refers to “Table S1 on page 18” but this table does not appear anywhere in the main text or supplementary materials. Moreover. Please verify if "Table S1" was included by mistake, and revise the text accordingly.

Comment 21 :

Page 19: The citation “Phu et al., [87]” appears to be incorrect. According to the reference list, it should be "Phu et al., [88]". Please revise the reference number accordingly to maintain consistency

Comment 22:

The equation provided for calculating the number of experiments in a Central Composite Design (CCD), 𝑁 = 2^k × 2k + C₀ is incorrect. The correct formula is:  𝑁 = 2^k + 2k + C₀

Comment 23:

Page 22: The term “DCOD” appears to be a typographical error and should be corrected. It is likely intended to be “COD”

Comment 24:

Similar remarks apply to Table 3. The title contains the same spelling error "Summery" should be corrected to "Summary." Moreover, unit notations should be uniformly presented throughout the table to ensure consistency. Additionally, in the row corresponding to reference [51], the software used is explicitly mentioned, whereas it is not provided for the other studies. It is therefore recommended to either indicate the software used for all referenced studies or remove it from reference [51] to maintain consistency.

In addition to the previous remarks, the earliest reference listed in the table dates from 2013, which covers only about 12 years, not 25. It is therefore recommended to either update the table with older references or adjust the title to reflect the accurate time span covered by the studies included.

Comment 25:

At the beginning of page 25, the phrase “Response Surface Methodology (RSM) with Box–Behnken design (BBD)” is repeated, although the abbreviations RSM and BBD have already been defined earlier in the manuscript.

Comment 26:

In the manuscript, the figures are referred to as “Figure 2S,” whereas in the supplementary materials, the correct notation is “Figure S2.” For consistency and clarity, the figure numbering should follow a uniform format throughout the manuscript and supplementary materials. The same correction applies to Figures S3, S4, S5, S6, and S7.

Comment 28:

The font style used in the table is inconsistent with the main text. It is important to ensure that the same font and formatting are applied throughout the manuscript, including all tables to maintain a professional and uniform appearance. This inconsistency is also noticeable in the second paragraph on page 34, where the font appears different from the rest of the text. Standardizing the font throughout the document is strongly recommended.

Comment 29:

Page 29: The reference number [63] should be added after “Moisés et al.”

Comment 30:

Tables 4, 5, and 6 are poorly organized and difficult to read. It is recommended to improve their layout by separating the rows more distinctly, for example by adding spacing or lines between entries.

Comment 31:

Page 35, Second paragraph: The statement “using current densities between 5 and 0 A·m^-2” is problematic, as a current density of 0 A·m^-2 implies that no current is applied, which contradicts the operation of an electrochemical process. Please revise this range to reflect realistic operational conditions  and ensure consistency with experimental feasibility.

Comment 32:

In Section 8, "Concluding Remarks and Future Research Perspectives,, the references in square brackets are not always presented consistently. Please ensure that all in-text references follow a uniform format in accordance with the journal's guidelines.

Comment 33:

Reference [35] in the reference list needs to be corrected. The journal name appears to be written in Chinese. It is recommended to provide the official English title of the journal.

Author Response

Responses to the Reviewers

 

Dear Editor

We highly appreciate your efforts in leading this esteemed high quality and recognized journal. We would like also to thank the five reviewers who have given deep intention and provide us with constructive comments. Actually, we considered all of their comments in preparing our revised manuscript, and we find that it is significantly improved to fulfill the journals scientific and editorial requirements. We hope that you will find that it is now suitable for publication.     

Responses to Reviewer 2

Comment 1: A thorough revision of Section 2.1 is recommended due to the presence of multiple misplaced commas (e.g., [31], k, n,….) which affect the readability of the text. Furthermore, key experimental details are lacking, including the nature of the organic effluent, the applied current density, the pH, the supporting electrolyte concentration, flow rate, reaction time, the type of electrodes employed and pollutant removal efficiency.

Response 1: Thank you for your valuable feedback. We have carefully revised Section 2.1 to correct the misplaced commas and improve overall readability. Additionally, we have updated the paragraph introducing Table 1 to provide more technical and experimental context, as you suggested. The revised text (highlighted in yellow in the manuscript) now explicitly summarizes the key operational and performance parameters from each study, including electrode materials and configurations, current density, pH, flow rate or HRT, and pollutant removal efficiencies. This added context allows for a clearer understanding of how EC performance varies across different wastewater types and strengthens the comparative value of Table 1.

Comment 2: For improved clarity and scientific rigor (Section 2.1), it is recommended to expand on the interpretation of the obtained results, as this would help readers better understand the significance and implications of the findings.

Response 2: Thank you for your valuable suggestion. We have revised Section 2.1 to include a clearer interpretation of the literature results. In particular, we now explain how key operational parameters (current density, electrode type, and pH) affect pollutant removal efficiency. We also briefly discuss the practical implications of these findings for energy use, process optimization, and treating different types of wastewater. All changes are highlighted in yellow in the revised manuscript.

 

Comment 3: It is recommended that the manuscript be carefully reviewed for consistency in the expression of units. The use of standardized scientific notation (e.g., mg·L^-1, g·L^-1, L·h^-1, $·m^-3…) should be applied uniformly throughout the text.

Response 3: Thank you for your helpful suggestion. We have thoroughly reviewed the manuscript to ensure consistency in the use of scientific units. Standardized SI notation is now applied uniformly throughout the text, tables, and figure captions. For example, concentrations are expressed as mg·L^-1 and g·L⁻¹, flow rates as L·h⁻¹, energy and cost units as kWh·m⁻³ and $·m⁻³, and current density as mA·cm⁻². These changes improve clarity and maintain consistency with scientific conventions. All revisions are highlighted in yellow in the updated manuscript.

 

Comment 4:The manuscript includes several abbreviations (e.g., COD, HRT, SEEC, TOC, DBO₅, R²…) that are not defined when first introduced. For clarity and readability, all abbreviations should be clearly defined upon their first occurrence.

Response 4: Thank you for your observation. We have carefully reviewed the manuscript and ensured that all abbreviations, including COD (Chemical Oxygen Demand), HRT (Hydraulic Retention Time), SEEC (Specific Electrical Energy Consumption), TOC (Total Organic Carbon), DBO₅ (Demande Biologique en Oxygène sur 5 jours, i.e., BOD₅), and R² (coefficient of determination), are now clearly defined upon their first occurrence in the text to improve clarity and readability. These changes have been highlighted in yellow in the revised manuscript.

 

Comment 5: In Section 2.1, the sentence regarding Moussavi et al. mentions that “the reaction constant increased with aeration, from 477 to 78 mL·g⁻¹·min⁻¹.”  However, the numerical values suggest a decrease rather than an increase. This inconsistency should be reviewed and corrected accordingly.

Response 5: Thank you for pointing out this inconsistency. We have corrected the sentence to reflect that the reaction constant decreased with aeration, from 477 to 78 mL·g⁻¹·min⁻¹. The revised sentence is now accurate and consistent with the reported values.

 

Comment 6: At the end of page 5, the phrase “During the past 25 years” should be corrected to “During the last 25 years” for proper usage in this context.

Response 6: Corrected as suggested. The phrase now reads “During the last 25 years.”

 

Comment 7: The citation format should be revised. The sequence “[2, 3, 28, 31–37] [38–47] [48–57] [58–61]” is incorrect and should be merged or reformatted appropriately.

Response 7: We have revised the citation format for clarity. The separate brackets have been merged into a single, continuous list: “[2, 3, 28, 31–61].”

 

Comment 8: Reference [61] is incorrectly attributed to Kumar et al.; it should be Purkait et al. This should be corrected.

Response 8: Thank you for noticing this error. The reference has been corrected [61] now correctly cites Purkait et al.

 

Comment 9: The highlighted passage beginning with “Fe rods… Response surface….”  needs to be reviewed and revised for clarity, accuracy, and proper sentence structure.

Response 9: This passage has been rewritten for clarity, grammar, and structure. It now clearly presents the experimental details and results related to Fe rods and the use of response surface methodology.

 

Comment 10: The expression 'using new Fe' in the context of Mehralian et al. (page 6) is ambiguous. Please clarify whether this refers to freshly introduced iron, a particular form or phase of iron, or another specific meaning.

Response 10: We have revised the phrase “new Fe” to “iron electrodes in a novel configuration” to more accurately describe the arrangement used in Mehralian et al.’s reactor design.

 

Comment 11: Table 1 should be carefully revised. The unit notations are not uniform throughout the table, and several abbreviations are used without being defined (e.g., WW, N°, TPH, TSS, MPP, BPS, NTU, MPS…). Additionally, the font style is inconsistent across different entries. It is also recommended to include the reaction time, as it is an important operational parameter for evaluating and comparing the treatment efficiency, and the table title “Table 1: Summery of main..” contains a spelling error “Summery” should be corrected to “Summary.”

Response 11: Table 1 has been thoroughly revised:

All unit notations now follow standard scientific format (e.g., mg·L⁻¹, A·m⁻², min).

All abbreviations (WW, TPH, TSS, MPP, NTU, etc.) have been defined in footnotes.

The table font style has been unified.

The title has been corrected to “Summary of main…”

 

Comment 12: On page 12,

the author name Mois´es et al.” contains a typographical error and should be corrected to Moisés et al.

Gunawan et al. is cited as reference [69], but it corresponds to [70].

Dan et al. is cited as [73], but the correct reference is [74].

For Ghernaout et al., the citation should be simply [63] the year 2010 should be removed.

Response 12: All corrections have been made:

“Mois´es et al.”  To “Moisés et al.”

Gunawan et al. is now correctly cited as [70].

Dan et al. is now cited as [74].

Ghernaout et al. is now cited simply as [63], and the year 2010 was removed.

 

Comment 13: The final paragraph on page 12 should be revised for clarity. The sentence mentioning Bani-Melhem et al., Makwana and Ahammed, Jiménez et al., Gil-Pavas et al., and Gunawan et al., along with various types of treated wastewater, lacks the use of the word “respectively”. This omission makes the associations between each study and the corresponding wastewater type unclear. It is recommended to correct this for better readability and accuracy.

Response 13: The sentence has been revised to include “respectively,” clarifying the link between studies and the wastewater types.

 

Comment 14: A revision of Table 2 is recommended. The title currently states 'since 20 years', yet the earliest reference listed is from 2010, which suggests 'since 15 years' would be more accurate. Additionally, unit formatting throughout the table should be reviewed and harmonized to ensure consistency and adherence to standard scientific notation. It is also important to define all abbreviations used in the table, such as ES, SBBR, UASB, etc., to ensure clarity and accessibility for all readers, and the table title “Table 2: Summery of main..” contains a spelling error “Summery” should be corrected to “Summary.”

Response 14: We have revised Table 2 as follows:

• Title corrected to “Summary of main…”
• All unit formats now follow SI standards.
• All abbreviations (ES, SBBR, UASB, etc.) have been defined in footnotes.
• The title now indicates “over the past 15 years” to match the actual publication range.

 

Comment 15: In Section 3.1.1 (page 16), the abbreviation “TSS” appears without prior definition. It is important to define all abbreviations at first use for instance, Also, the author name “Maheshet al.” in the last paragraph contains a typographical error and should be corrected to “Mahesh et al.”

Response 15: “TSS” is now defined at its first mention. The typographical error has been corrected to “Mahesh et al.”

Comment 16: In Equation (1), the symbols F, I, and Δt are not defined in the text. These should be properly introduced to ensure clarity for the reader. Additionally, the term ET should be defined.

Response 16: All variables in Equation (1) have been defined in the text for clarity.

 

Comment 17: The section numbering appears to be incorrect. "3.1.1. Combined processes" should be labeled as "3.1.2"

Response 17: Section numbering has been corrected accordingly.

 

Comment 18: The citation "Gunawan et al., [7]" should be corrected to "Gunawan et al., [70]" to ensure consistency with the reference list.

Response 18: Corrected as suggested.

 

Comment 19: In Equation (3), the term C should be replaced with C_t to accurately reflect the concentration at time t. Additionally, the relevance of reference [90] to the preceding sentence is unclear and should be reconsidered.

Response 19: The symbol has been corrected to Ct. Reference [90] has been reviewed and kept as Equation (3) was related to that reference

 

Comment 20: The manuscript refers to “Table S1 on page 18” but this table does not appear anywhere in the main text or supplementary materials. Moreover. Please verify if "Table S1" was included by mistake, and revise the text accordingly.

 

Response 20: Thank you for your observation. The reference to “Table S1 on page 18” in the manuscript was accurate in content but incorrectly labeled elsewhere. The table in question is correctly numbered as Table S1 in the supplementary materials. We have revised the text to consistently use “Table S1” throughout the manuscript and ensured the table is properly included and labeled in the supplementary file.

 

 

Comment 21 : Page 19: The citation “Phu et al., [87]” appears to be incorrect. According to the reference list, it should be "Phu et al., [88]". Please revise the reference number accordingly to maintain consistency

Response 21: Corrected to [88] as per the reference list.

 

Comment 22: The equation provided for calculating the number of experiments in a Central Composite Design (CCD), ? = 2k × 2k + C0 is incorrect. The correct formula is:  ? = 2k + 2k + C0

Response 22: The equation has been corrected to: N = 2k + 2k + C₀.

 

 

Comment 23: Page 22: The term “DCOD” appears to be a typographical error and should be corrected. It is likely intended to be “COD”

Response 23: Thank you for your comment. In this context, DCOD was intentionally used to indicate Chemical Oxygen Demand degradation, referring to the reduction or removal of COD during treatment. To avoid confusion, we have now clarified this in the text and defined DCOD upon first use. All changes are highlighted in yellow in the revised manuscript.

 

Comment 24: Similar remarks apply to Table 3. The title contains the same spelling error "Summery" should be corrected to "Summary." Moreover, unit notations should be uniformly presented throughout the table to ensure consistency. Additionally, in the row corresponding to reference [51], the software used is explicitly mentioned, whereas it is not provided for the other studies. It is therefore recommended to either indicate the software used for all referenced studies or remove it from reference [51] to maintain consistency.

In addition to the previous remarks, the earliest reference listed in the table dates from 2013, which covers only about 12 years, not 25. It is therefore recommended to either update the table with older references or adjust the title to reflect the accurate time span covered by the studies included.

 

Response 24: Title corrected to “Summary…”

Unit formats standardized.

Software mention from [51] was removed for consistency.

Title now reflects the accurate time span: “studies published since 2013.”

 

Comment 25: At the beginning of page 25, the phrase “Response Surface Methodology (RSM) with Box–Behnken design (BBD)” is repeated, although the abbreviations RSM and BBD have already been defined earlier in the manuscript.

Response 25: The repetition has been removed for conciseness.

 

Comment 26: In the manuscript, the figures are referred to as “Figure 2S,” whereas in the supplementary materials, the correct notation is “Figure S2.” For consistency and clarity, the figure numbering should follow a uniform format throughout the manuscript and supplementary materials. The same correction applies to Figures S3, S4, S5, S6, and S7.

Response 26: Thank you for your valuable observation. We acknowledge the inconsistency in figure numbering between the manuscript and the supplementary materials. The references to the supplementary figures have been corrected throughout the manuscript to follow the uniform and standard format as “Figure S2,” “Figure S3,” “Figure S4,” “Figure S5,” “Figure S6,” and “Figure S7,” in line with the notation used in the supplementary materials. This ensures consistency and clarity for readers.

 

Comment 28: The font style used in the table is inconsistent with the main text. It is important to ensure that the same font and formatting are applied throughout the manuscript, including all tables to maintain a professional and uniform appearance. This inconsistency is also noticeable in the second paragraph on page 34, where the font appears different from the rest of the text. Standardizing the font throughout the document is strongly recommended.

Response 28: Font formatting has been standardized across the entire manuscript and tables.

 

Comment 29:Page 29: The reference number [63] should be added after “Moisés et al.”

Response 29: Reference [63] has been added as suggested.

 

Comment 30: Tables 4, 5, and 6 are poorly organized and difficult to read. It is recommended to improve their layout by separating the rows more distinctly, for example by adding spacing or lines between entries.

Response 30: Tables 4, 5, and 6 have been reformatted with clear row separation and improved layout for readability.

 

Comment 31:Page 35, Second paragraph: The statement “using current densities between 5 and 0 A·m^-2” is problematic, as a current density of 0 A·m^-2 implies that no current is applied, which contradicts the operation of an electrochemical process. Please revise this range to reflect realistic operational conditions  and ensure consistency with experimental feasibility.

 

Response 31: Revised to reflect a realistic range: “between 5 and 20 A·m⁻² which is equivalent to 0.5 and 2 mA·cm^-2 for units’ consistency.”

 

Comment 32:

In Section 8, "Concluding Remarks and Future Research Perspectives,, the references in square brackets are not always presented consistently. Please ensure that all in-text references follow a uniform format in accordance with the journal's guidelines.

All references in Section 8 have been reviewed and standardized per journal style.

 

Comment 33: Reference [35] in the reference list needs to be corrected. The journal name appears to be written in Chinese. It is recommended to provide the official English title of the journal.

Response 33: We have updated Reference [35] with the official English title of the journal, The correct one is: J. Korean Chem. Soc.

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

This review deals with the use of continuous electrocoagulation (EC) processes for the treatment of industrial organic pollutants. While the topic is relevant, the manuscript in its current form lacks the scientific rigor and depth expected from a comprehensive review. A major revision is required to address serious structural, conceptual, and editorial weaknesses.

Major comments

1. Lack of critical analysis and added value: The manuscript predominantly summarizes results from previous studies without offering any meaningful insight, synthesis, or critical evaluation. Many paragraphs simply describe experimental parameters and outcomes of individual studies without comparative discussion or identification of research gaps. Several phrases are presented within quotation marks, which creates confusion: it is unclear whether these are direct citations or if the authors are distancing themselves from the terms. 

2. No bibliometric methodology described: The authors fail to describe the bibliographic strategy used to build the review. There is no information on the search engines employed, the keywords used, or the inclusion/exclusion criteria. Without this methodological transparency, the comprehensiveness and reproducibility of the review cannot be assessed.

3. Poor figure quality: Many figures appear to be directly taken from the referenced articles without modification or critical discussion. Several figures are of low resolution and lack proper explanation in the main text. Also, it is unclear whether the authors have obtained the necessary permissions to reproduce these images.

4. Overloaded and redundant tables: Tables 1–3 are excessively long and dense, often repeating data that could be synthesized or referenced instead. These tables would benefit from being streamlined, with key trends or comparisons highlighted rather than raw data compilation.

5. Weak structure and narrative: The manuscript lacks a coherent thematic flow. Section transitions are abrupt, and there is little effort to build a consistent argument or storyline. Many parts read like a patchwork of summaries, rather than a cohesive and insightful review.

6. Language and editorial issues: The manuscript contains frequent grammatical errors, awkward phrasing, and inconsistent terminology. A thorough language revision by a fluent English speaker or professional editor is strongly recommended.

7. Shallow conclusions and limited perspectives: The final sections do not extract key takeaways from the literature nor provide clear directions for future research. A high-quality review should help guide researchers by highlighting unresolved questions, emerging trends, and promising directions, none of which are clearly presented.

I'd suggest to add a conceptual figure or diagram to clarify the role of continuous EC in integrated treatment systems.

Author Response

Responses to the Reviewers

 

Dear Editor

We highly appreciate your efforts in leading this esteemed high quality and recognized journal. We would like also to thank the five reviewers who have given deep intention and provide us with constructive comments. Actually, we considered all of their comments in preparing our revised manuscript, and we find that it is significantly improved to fulfill the journals scientific and editorial requirements. We hope that you will find that it is now suitable for publication.     

Responses to Reviewer 3

General Comment: This review deals with the use of continuous electrocoagulation (EC) processes for the treatment of industrial organic pollutants. While the topic is relevant, the manuscript in its current form lacks the scientific rigor and depth expected from a comprehensive review. A major revision is required to address serious structural, conceptual, and editorial weaknesses.

Response: We thank the reviewer for the critical and constructive feedback. In response, we have undertaken a comprehensive revision of the manuscript to significantly improve its scientific depth, structural coherence, and editorial quality. The following key actions have been implemented:

• Scientific rigor: We expanded the conclusion section to provide a more detailed mechanistic explanation of key technical challenges such as electrode passivation and sludge management, and incorporated specific insights related to pollutant chemistry and EC performance variability.
• Conceptual clarity: The scope of “organic pollutants” has been explicitly defined in the Introduction, with clarification on the inclusion of emerging contaminants such as PFAS, to ensure conceptual transparency and boundary definition.
• Structural enhancement: We reviewed the organization of the manuscript and ensured logical flow between sections, particularly in the discussions on process performance, modeling, and design innovations.
• Literature completeness: We incorporated recent developments in water treatment technologies (2022–2024) to strengthen the literature context and inserted a new paragraph describing the literature search methodology (databases, keywords, inclusion criteria).
• Editorial improvements: The manuscript has been thoroughly proofread to correct formatting inconsistencies, character encoding issues, and unit usage (e.g., mA/cm² vs. A/m²), and to ensure consistent mathematical notation throughout.

We believe these revisions address the reviewer's concerns and significantly enhance the overall quality, clarity, and scholarly value of the manuscript.

Comment 1: Lack of critical analysis and added value: The manuscript predominantly summarizes results from previous studies without offering any meaningful insight, synthesis, or critical evaluation. Many paragraphs simply describe experimental parameters and outcomes of individual studies without comparative discussion or identification of research gaps. Several phrases are presented within quotation marks, which creates confusion: it is unclear whether these are direct citations or if the authors are distancing themselves from the terms. 

Response:   We sincerely thank the reviewer for this valuable observation. In response, we have carefully revised the manuscript to go beyond a descriptive summary and instead provide critical analysis and thematic synthesis across the reviewed studies. Specifically:

• We introduced comparative commentary throughout the sections on standalone and combined EC processes to highlight performance trends, contrast operational conditions, and evaluate the relative effectiveness of different configurations.
• Where applicable, we have drawn attention to gaps in the literature, including limited long-term performance data, challenges in full-scale implementation, and the need for standardization in reactor design and modeling approaches.
• In the revised conclusion and future research perspectives, we explicitly discuss the limitations of current CECP research and outline targeted research needs, thus enhancing the manuscript’s added value to the field.
• Regarding the use of quotation marks, we have thoroughly reviewed the manuscript to eliminate unnecessary or ambiguous quotations. All remaining quotations are now clearly identified either as direct citations from literature or reformulated for clarity in the authors’ own voice.

We believe these revisions address the reviewer’s concerns and improve the analytical rigor and interpretive depth of the review.

Comment 2: No bibliometric methodology described: The authors fail to describe the bibliographic strategy used to build the review. There is no information on the search engines employed, the keywords used, or the inclusion/exclusion criteria. Without this methodological transparency, the comprehensiveness and reproducibility of the review cannot be assessed.

Response: We thank the reviewer for highlighting this important point. To improve the methodological transparency and reproducibility of our review, we have included a clear description of the bibliographic strategy used to compile the literature. Specifically, we have inserted a new paragraph to provide the following information:

“Data were collected from Scopus and Web of Science databases using the search terms: ‘continuous electrocoagulation’ AND ‘organic pollutant’ OR ‘industrial wastewater’ in titles, abstracts, and keywords. The search included peer-reviewed journal articles published between 2000 and 2025. Duplicates were removed, and only English-language articles focusing on continuous (non-batch) EC applications were included.”

This addition outlines the databases, keywords, timeframe, and inclusion/exclusion criteria used in our literature review. We believe this revision significantly improves the comprehensiveness and methodological clarity of the manuscript.

Comment 3: Poor figure quality: Many figures appear to be directly taken from the referenced articles without modification or critical discussion. Several figures are of low resolution and lack proper explanation in the main text. Also, it is unclear whether the authors have obtained the necessary permissions to reproduce these images.

Response:   We thank the reviewer for pointing out these important concerns regarding figure quality, originality, and integration into the manuscript. In response, we have undertaken the following actions:

• Figure Quality Improvement: All figures have been reviewed and replaced where necessary with higher-resolution versions to ensure clear visibility and professional presentation.
• Originality and Permissions: We have removed figures that were directly reproduced from other publications without substantial modification or where permissions could not be obtained. In their place, we have created original schematic illustrations or revised versions that synthesize key concepts with proper attribution. Where reproduction of figures was essential and permitted, we got formal permission from the copyright holders and have noted this accordingly under each figure.
• Enhanced Integration: We have revised the main text to include critical discussion and contextual explanation of each figure, ensuring that all visuals are not only descriptive but also serve to support and interpret key findings and comparisons in the review.

We believe these revisions resolve the issues raised and significantly improve the clarity, originality, and scholarly contribution of the visual content.

Comment 4: Overloaded and redundant tables: Tables 1–3 are excessively long and dense, often repeating data that could be synthesized or referenced instead. These tables would benefit from being streamlined, with key trends or comparisons highlighted rather than raw data compilation.

Response:   We appreciate the reviewer’s observation regarding the structure and content of Tables 1–3. In response, we have thoroughly revised and streamlined these tables to improve readability and emphasize key insights. Specifically:

• Redundancies were removed by eliminating repetitive data entries and consolidating similar study outcomes.
• Summarized formats were adopted to present only the most relevant parameters, performance metrics, and conditions, avoiding unnecessary detail.
• Where appropriate, we replaced extensive data listings with representative examples and included narrative summaries in the main text to contextualize broader trends and findings.
• We also ensured that each table now highlights comparative patterns or critical differences across studies, thus enhancing their analytical value.

We believe these changes significantly improve the clarity, conciseness, and usefulness of the tables in supporting the manuscript’s review objectives.

Comment 5: Weak structure and narrative: The manuscript lacks a coherent thematic flow. Section transitions are abrupt, and there is little effort to build a consistent argument or storyline. Many parts read like a patchwork of summaries, rather than a cohesive and insightful review.

Response:   We appreciate the reviewer’s critical feedback regarding the manuscript’s structure and narrative coherence. In response, we have made substantial revisions to enhance the thematic continuity and logical flow throughout the review. Specifically:

• We reorganized several sections to follow a more natural progression—from fundamental principles of continuous electrocoagulation, to standalone applications, combined/hybrid systems, modeling approaches, and then to full-scale implementation and sustainability aspects.
• Transitional sentences and linking paragraphs have been added between major sections to guide the reader and reinforce a consistent storyline throughout the manuscript.
• We placed greater emphasis on synthesizing insights across studies, rather than presenting isolated summaries, to support a more integrated and critical perspective.
• The revised conclusion now clearly connects back to the major challenges and research gaps discussed earlier, ensuring the review ends with a cohesive and forward-looking summary.

We believe these changes have significantly improved the narrative structure and made the review more cohesive, engaging, and insightful for readers.

Comment 6: Language and editorial issues: The manuscript contains frequent grammatical errors, awkward phrasing, and inconsistent terminology. A thorough language revision by a fluent English speaker or professional editor is strongly recommended.

Response: We appreciate the reviewer’s observation. A thorough proofreading of the manuscript has been conducted to correct formatting inconsistencies, resolve character encoding issues, and ensure overall clarity and consistency. We have carefully reviewed the entire document to enhance its readability and ensure it meets the publication standards.

Comment 7: Shallow conclusions and limited perspectives: The final sections do not extract key takeaways from the literature nor provide clear directions for future research. A high-quality review should help guide researchers by highlighting unresolved questions, emerging trends, and promising directions, none of which are clearly presented.

Response: We thank the reviewer for this valuable suggestion. In response, we have substantially revised and expanded Section 8: Concluding Remarks and Future Research Perspectives to explicitly address key technical challenges that hinder the broader implementation of continuous electrocoagulation processes (CECPs). The revised section now includes a detailed discussion on electrode passivation mechanisms, highlighting their causes, operational impacts, and potential mitigation strategies such as self-cleaning electrodes and alternating current operation. Additionally, we have elaborated on sludge management constraints, including sludge separation, handling, and valorization. These additions are intended to provide a more comprehensive overview of the technical limitations and guide future research directions in this field. The revised section also includes appropriate references to support the discussion.

Comment 8: I'd suggest to add a conceptual figure or diagram to clarify the role of continuous EC in integrated treatment systems.

Response:   We thank the reviewer for this helpful suggestion. In response, we have added a new conceptual figure that illustrates the role of continuous electrocoagulation (EC) within integrated wastewater treatment systems. The figure outlines typical hybrid configurations, showing how CECPs can be effectively combined with other processes such as biological treatment, adsorption, membrane filtration, and advanced oxidation. It also highlights the position of CECPs within the treatment train either as a primary treatment step for turbidity and color removal or as a polishing step for organic or inorganic residuals. This figure has been inserted in the section discussing combined and hybrid CECP applications, and a corresponding explanation has been added to the main text to guide interpretation and underscore its relevance. We believe this addition enhances conceptual clarity and provides readers with a visual synthesis of integrated CECP strategies.

The conceptual diagram, Fig. 2 , has been inserted and discussed in Sec. 2.2

 

 

Fig 2. Conceptual integration of continuous electrocoagulation (CECP) within hybrid wastewater treatment systems. The diagram illustrates CECP’s flexibility to serve as a primary, intermediate, or polishing treatment step in combination with physical, chemical, and biological processes.

 

 

 

 

Reviewer 4 Report

Comments and Suggestions for Authors

Summary and general comments

This review paper covers the continuous electrocoagulation system. While the reviews is comprehensive, there are some deficiencies. There are also many minor and English errors. Please see the specific comments below for details.

Specific Comments

1. It is observed that the font size and type vary in many of the paragraph, and consistency is required.
2. The line number are not aligned.
3. Language needs to be polished. Word redundancy needs to be reduced. In abstract, replaced “ the published research” with the word “literature”. “will be” replaced with “is”. Section 2.1. A sentence that ended midway. “Abdul Rahmal et al applied…. and. According to their results,…”. Tables 2,3 “summery”. It is the responsibility of the authors to ensure that the minor errors are kept to a minimum.
4. The introduction also lacks a clear problem statement. What is the research gap addressed by this review? Authors briefly mentioned that the batch system is mostly focused on in most reviews, and this review is meant to focus on the continuous system. The sentence should be rewritten to make it more straightforward and clear.
5. Figure 1. From which database was this data obtained? Why is the search date not mentioned?
6. Since this review focuses on continuous systems, the authors should give a brief background on what a continuous EC system is and how it differs from a batch EC system. What are the limitations of the batch EC system? Justify the focus on a continuous system.
7. What is a standalone? What are combined? Even if some of this terminology may seem obvious, it should all be defined on its first appearance.
8. Section 2.1. The lack of description of these explored parameters, such as current density. Reaction constant k and electrode number n are a concern. A Review paper should be standalone.
9. Section 2.1. The acronym SUS is not defined.
10. Section 2.1. When discussing removal efficiency, it is essential to consider the starting condition, especially the initial pollutant concentration. This should also be included in Table 1.
11. Section 2.1. RSM and BBD are not described. The intention of these tools is usually to optimise the process and identify the conditions for the highest removal efficiency.
12. Table 1. Column “pH, T.” Some of the temperature values are missing. It is also not clear what is electrode SS
13. Authors are using both “L” and “l” to represent litre. This should be kept consistent.
14. The format of the unit should also be kept consistent. In Section 1, g/L-1 is observed while in subsequent sections, g/L is used instead.
15. Recheck the text below the Figure 2 caption. It appears that the authors are using a screenshot of the text, rather than formatting it properly in text.
16. Section 3.1. There is an oversimplification of the models. How is the fitting of kinetic and isotherm models determined? Are there any metrics, such as R-squared or error function, that can justify their accuracy? Langmuir and Freundlich are mentioned once in this section. It is assumed that this refers to the adsorption process rather than EC. Authors should be careful in describing a model relevant to the EC process.
17. It seems that the rules of using acronyms in scientific writing are not followed. Authors should consult online sources for guidance on how to do this properly.
18. It seems that section 3.2 is unrelated to section 3. A new header should be given, as Section 3.2 is more closely related to the use of mathematical tools for optimisation instead of kinetic or isotherm modelling. RSM and BBD are also described in the earlier section in Section 2. Authors should be careful not to repeat. The lack of discussion regarding the usefulness of these tools is a concern
19. Is Figure 11 referring to both batch and continuous systems? Or just the continuous system?
20. It is not clear what authors are using the LCA for. Is it to calculate the carbon footprint or the energy? What exactly is measured? What insights are obtained?
21. The conclusion can be improved. The normal conclusion is a single paragraph and should not contain any citations. Future work can be a section 8 by itself, followed by the conclusion section.
22. Supplementary section. If any of these figures are obtained from literature, it should be cited correctly. The citation for the supplementary section should restart from 1. Recheck the journal guidelines if the format of the supplementary table and figure is Table S1 or Table 1S. Normally, Table S1 is used.

Comments on the Quality of English Language

See specific comments. Authors should take the responsibility to recheck the manuscript for all potential errors to reduce the minor English errors and reduce word redundancy.

Author Response

Responses to the Reviewers

 

Dear Editor

We highly appreciate your efforts in leading this esteemed high quality and recognized journal. We would like also to thank the five reviewers who have given deep intention and provide us with constructive comments. Actually, we considered all of their comments in preparing our revised manuscript, and we find that it is significantly improved to fulfill the journals scientific and editorial requirements. We hope that you will find that it is now suitable for publication.     

Resposes to Reviewer 4

This review paper covers the continuous electrocoagulation system. While the reviews is comprehensive, there are some deficiencies. There are also many minor and English errors. Please see the specific comments below for details.

Specific Comments

Comment 1: It is observed that the font size and type vary in many of the paragraph, and consistency is required.

Response 1: Thank you for pointing this out. The entire manuscript has been carefully revised to ensure consistency in font size and style throughout, following the journal's formatting guidelines.

Comment 2: The line number are not aligned.

Response 2: The line numbers have been realigned and formatted correctly in the revised manuscript.

Comment 3: Language needs to be polished. Word redundancy needs to be reduced. In abstract, replaced “ the published research” with the word “literature”. “will be” replaced with “is”. Section 2.1. A sentence that ended midway. “Abdul Rahmal et al applied…. and. According to their results,…”. Tables 2,3 “summery”. It is the responsibility of the authors to ensure that the minor errors are kept to a minimum.

Response 3: Thank you for your careful review. We have polished the manuscript to improve clarity and reduce redundancy. Specifically, we have revised the abstract by replacing “the published research” with “the literature” and “will be” with “is.” The incomplete sentence in Section 2.1 has been corrected for clarity. Additionally, the spelling errors in Tables 2 and 3 (“summery”) have been corrected to “summary.” We have also thoroughly proofread the manuscript to minimize minor errors.

Comment 4: The introduction also lacks a clear problem statement. What is the research gap addressed by this review? Authors briefly mentioned that the batch system is mostly focused on in most reviews, and this review is meant to focus on the continuous system. The sentence should be rewritten to make it more straightforward and clear.

Response 4: Thank you for your comment. We appreciate this suggestion. A clear and concise problem statement has been added at the end of the Introduction section to highlight the research gap and justify the focus on continuous electrocoagulation (EC) systems.

Comment 5: Figure 1. From which database was this data obtained? Why is the search date not mentioned?

Response 5: Thank you for your valuable suggestion. We have updated the caption of Figure 1 to specify the data source and search details. The data were collected from the Scopus and Web of Science databases using the search terms: “continuous electrocoagulation” AND “organic pollutant” OR “industrial wastewater” in titles, abstracts, and keywords. The search covered peer-reviewed articles published from 2000 to 2025. Duplicates and non-English articles were excluded, focusing only on continuous (non-batch) EC studies. This clarification improves transparency and reproducibility.

Comment 6: Since this review focuses on continuous systems, the authors should give a brief background on what a continuous EC system is and how it differs from a batch EC system. What are the limitations of the batch EC system? Justify the focus on a continuous system.

Response 6:  A detailed explanation distinguishing continuous from batch EC systems has been added.

Comment 7: What is a standalone? What are combined? Even if some of this terminology may seem obvious, it should all be defined on its first appearance.

Response 7: The terms standalone and combined have now been clearly defined in the revised paragraph at their first appearance.

Comment 8: Section 2.1. The lack of description of these explored parameters, such as current density. Reaction constant k and electrode number n are a concern. A Review paper should be standalone.

Response 8: We thank the reviewer for this valuable observation. To ensure the manuscript is fully standalone, we have added clear definitions and explanations of the key experimental parameters discussed in Section 2.1, including current density, reaction constant (k), and electrode number (n). These parameters are now briefly described to help readers unfamiliar with the technical details understand their significance and role in continuous EC processes.

 

Comment 9: Section 2.1. The acronym SUS is not defined.

Response 9: Thank you for pointing this out. The acronym “SUS” was used by mistake. It has now been corrected to “SS” and is properly defined upon its first use as stainless steel (SS) in Section 2.1 to ensure consistency throughout the manuscript.

 

Comment 10: Section 2.1. When discussing removal efficiency, it is essential to consider the starting condition, especially the initial pollutant concentration. This should also be included in Table 1.

Response 10: Thank you for this comment. All available data about the initial concentaration are added in a separate column before that of RE%.

Comment 11: Section 2.1. RSM and BBD are not described. The intention of these tools is usually to optimise the process and identify the conditions for the highest removal efficiency.

Response 11: Thank you for pointing this out. We have revised the relevant sections in Section 2.1 to include clear definitions and context for both Response Surface Methodology (RSM) and Box–Behnken Design (BBD). These clarifications have been added where RSM and BBD are first mentioned (references [58] and [60], respectively) to ensure that the manuscript remains self-contained and accessible to all readers.

 

Comment 12: Table 1. Column “pH, T.” Some of the temperature values are missing. It is also not clear what is electrode SS

Response 12: We appreciate the reviewer’s careful observation. In response:

1. Clarification of "SS": We have updated the table to clarify that "SS" refers to stainless steel electrodes, as noted in the list of abbreviations at the end of the table. This has now been stated more explicitly to avoid ambiguity.
2. Missing Temperature Values: Where available, we have filled in the missing temperature (T) values by reviewing the original articles. For studies where temperature data was not reported, we have indicated this clearly using “NR” (Not Reported) to maintain transparency.
3. Improved Table Clarity: To enhance readability, we have reformatted the column headers (e.g., “pH, T” changed to “pH / T (°C)”), ensured unit consistency across all entries, and double-checked all operational parameters for accuracy.

 

Comment 13: Authors are using both “L” and “l” to represent litre. This should be kept consistent.

Comment 14: The format of the unit should also be kept consistent. In Section 1, g/L-1 is observed while in subsequent sections, g/L is used instead.

Response 13 and 14 : All units have been revised for consistency using standardized scientific notation such as mg·L⁻¹, g·L⁻¹, L·h⁻¹, and $·m⁻³, following SI unit guidelines. “L” (uppercase L) is used uniformly for litre.

Comment 15: Recheck the text below the Figure 2 caption. It appears that the authors are using a screenshot of the text, rather than formatting it properly in text.

Response 15: We thank the reviewer for this valuable observation. The text below Figure 2 has been carefully revised. We have removed the screenshot and replaced it with properly formatted editable text in accordance with the journal’s formatting guidelines. Additionally, the figure caption has been rewritten to enhance clarity and accuracy. The current version reads:

 

Comment 16: Section 3.1. There is an oversimplification of the models. How is the fitting of kinetic and isotherm models determined? Are there any metrics, such as R-squared or error function, that can justify their accuracy? Langmuir and Freundlich are mentioned once in this section. It is assumed that this refers to the adsorption process rather than EC. Authors should be careful in describing a model relevant to the EC process.

Response 16: We thank the reviewer for this insightful comment. In response, we have revised Section 3.1 to clarify how kinetic and isotherm models were applied and how their fit was assessed. Specifically:

• We now state that the kinetic models (first- and second-order) were fitted using plots such as ln(C/Co) versus time, and the quality of fit was evaluated using correlation coefficients (R² values), as reported in the referenced studies.
• We clarified that Langmuir and Freundlich isotherm models were applied only to describe the adsorption of pollutants onto electrochemically generated coagulants, not the overall EC process. This is now explicitly mentioned to prevent any confusion.
• Additionally, the Bohart–Adams model used for adsorption in a packed bed reactor (post-EC stage) has been more thoroughly explained, including how the fitting parameters are estimated.

These clarifications ensure that the modeling efforts discussed in the manuscript are both accurately represented and properly contextualized for EC applications.

 

Comment 17: It seems that the rules of using acronyms in scientific writing are not followed. Authors should consult online sources for guidance on how to do this properly.

Response 17: Thank you for your valuable feedback regarding the use of acronyms in our manuscript. We have carefully reviewed the entire text to ensure that acronyms are introduced correctly upon first use, defined clearly, and used consistently throughout the paper in accordance with standard scientific writing conventions. We consulted relevant style guides and online resources to adhere to best practices in acronym usage. We appreciate your attention to this detail, which has helped improve the clarity and readability of our work.

 

Comment 18: It seems that section 3.2 is unrelated to section 3. A new header should be given, as Section 3.2 is more closely related to the use of mathematical tools for optimisation instead of kinetic or isotherm modelling. RSM and BBD are also described in the earlier section in Section 2. Authors should be careful not to repeat. The lack of discussion regarding the usefulness of these tools is a concern

Response 18: Thank you for your valuable observation regarding Section 3.2. We agree that the section focuses on optimization tools which differ from kinetic and isotherm modeling discussed in earlier subsections. However, as Section 3 broadly addresses mathematical modeling of continuous electrocoagulation processes, it includes both mechanistic/kinetic modeling and optimization methodologies such as RSM and BBD. This is because optimization techniques are a crucial part of mathematical modeling, helping to identify efficient operational parameters and improve process performance. Additionally, we have refined the discussion to minimize repetition of RSM and BBD descriptions from Section 2, and expanded the explanation of their practical utility in optimizing EC systems. We believe these revisions clarify the relationship between the different modeling approaches within the overall mathematical modeling framework of continuous EC processes.

 

Comment 19: Is Figure 11 referring to both batch and continuous systems? Or just the continuous system?

Response 19: Thank you for the insightful comment. Figure 11 represents studies on LCA applied to both batch and continuous EC systems. As continuous systems are still relatively limited in number, we have specifically identified and discussed those cases in the main text. The figure presents the overall distribution of LCA-related EC studies to give a complete overview of the field’s progress. To avoid confusion, we have revised the figure caption and corresponding text to explicitly mention that it includes both batch and continuous systems, with continuous cases highlighted in the discussion.

 

Comment 20: It is not clear what authors are using the LCA for. Is it to calculate the carbon footprint or the energy? What exactly is measured? What insights are obtained?

Response 20: Thank you for your valuable comment. We have clarified that the LCA in our study is used to evaluate key environmental impacts of electrocoagulation processes, specifically quantifying the carbon footprint (global warming potential) and energy consumption across the treatment life cycle. The LCA results provide insights into major impact drivers such as electricity usage and electrode materials, helping to guide optimization for improved environmental sustainability. Relevant text has been revised accordingly.

Comment 21:The conclusion can be improved. The normal conclusion is a single paragraph and should not contain any citations. Future work can be a section 8 by itself, followed by the conclusion section.

Thank you for your comment. We have revised the manuscript by creating a separate Future Work section (Section 8) and making the Conclusion a single paragraph without citations. We also expanded the conclusion to include key technical challenges such as electrode passivation and sludge management, based on feedback from another reviewer. This gives a clearer summary and outlook for future research.

Comment 22: Supplementary section. If any of these figures are obtained from literature, it should be cited correctly. The citation for the supplementary section should restart from 1. Recheck the journal guidelines if the format of the supplementary table and figure is Table S1 or Table 1S. Normally, Table S1 is used.

Response 22: All supplementary figures and tables have been reviewed and correctly cited where necessary. The figure/table format has been standardized as “Table S1,” “Figure S2,” etc., and supplementary citations have been renumbered to restart from 1, following the journal’s guidelines.

 

 

Reviewer 5 Report

Comments and Suggestions for Authors

This manuscript presents a thorough review of continuous electrocoagulation processes (CEP) for industrial organic pollution treatment. The work demonstrates well-organized structure and substantial data support, systematically examining CEP’s process performance, mathematical modeling, design innovations, full-scale implementations, circular economy integration, and life cycle assessment. The 25-year research synthesis offers valuable academic insights, though several aspects require refinement:

1. Figure 1 annotations should specify the literature search methodology, including databases utilized and exact search terms.

2. The introduction should explicitly define the scope of “organic pollutants” - particularly whether emerging contaminants (e.g., PFAS) are encompassed within the review scope.

3. Recent advancements (past 2-3 years) in water treatment technologies should be incorporated in the introduction to strengthen the literature context.

4. Page 11’s discussion of CEP’s superior chromaticity/turbidity removal versus lower COD/TOC efficiency requires mechanistic explanation, particularly regarding organic molecular stability variations.

5. Unit standardization is necessary throughout (e.g., reconcile mA/cm² with A/m² usage).

6. Mathematical expressions require consistent italicization of physical quantity symbols per standard conventions.

7. The current reference list appears disproportionately weighted toward the Al-Qodah research group. A more balanced citation approach incorporating contrasting viewpoints would strengthen scholarly rigor.

8. The conclusion section should expand to address key technical challenges, including but not limited to electrode passivation mechanisms and sludge management constraints.

9. Manuscript requires thorough proofreading to resolve formatting irregularities (e.g., character encoding issues) prior to publication.

Author Response

Responses to the Reviewers

 

Dear Editor

We highly appreciate your efforts in leading this esteemed high quality and recognized journal. We would like also to thank the five reviewers who have given deep intention and provide us with constructive comments. Actually, we considered all of their comments in preparing our revised manuscript, and we find that it is significantly improved to fulfill the journals scientific and editorial requirements. We hope that you will find that it is now suitable for publication.     

 

Responses to Reviewer 5

General comment: This manuscript presents a thorough review of continuous electrocoagulation processes (CEP) for industrial organic pollution treatment. The work demonstrates well-organized structure and substantial data support, systematically examining CEP’s process performance, mathematical modeling, design innovations, full-scale implementations, circular economy integration, and life cycle assessment. The 25-year research synthesis offers valuable academic insights, though several aspects require refinement:

Response: We sincerely thank the reviewer for the positive and encouraging feedback regarding the structure, comprehensiveness, and academic value of our manuscript. We are pleased that the organization and breadth of the review were recognized. In response to the reviewer’s specific and constructive suggestions for refinement, we have carefully revised the manuscript to enhance clarity, ensure consistency, and address all points raised, including expanding the conclusion to discuss key technical challenges, standardizing units, correcting formatting issues, clarifying the pollutant scope, and diversifying references. We believe these revisions significantly strengthen the manuscript, and we are grateful for the reviewer’s guidance in improving its overall quality.

Comment 1: Figure 1 annotations should specify the literature search methodology, including databases utilized and exact search terms.

Response: We thank the reviewer for this valuable suggestion. To address this comment, we have inserted the following text directly preceding Figure 1 to include a clear description of the literature search methodology:

“Data in Fig. 1were collected from Scopus and Web of Science databases using the search terms: “continuous electrocoagulation” AND “organic pollutant” OR “industrial wastewater” in titles, abstracts, and keywords. The search included peer-reviewed journal articles published between 2000 and 2025 since EC is a recent technology and it is rarely cited before year 2000. Duplicates were removed, and only English-language articles focusing on continuous (non-batch) EC applications were included.”

This addition ensures transparency in the data collection process and improves the reproducibility and clarity of the literature analysis presented in Figure 1.

Comment 2: The introduction should explicitly define the scope of “organic pollutants” - particularly whether emerging contaminants (e.g., PFAS) are encompassed within the review scope.

Response: We thank the reviewer for this insightful comment. To clarify the scope of “organic pollutants” considered in the review, we have added a new text in the third paragraph of the Introduction. The inserted paragraph explicitly defines the types of organic pollutants covered and addresses the inclusion of emerging contaminants such as PFAS. The added paragraph reads as follows:

“In this review, the term organic pollutants encompass a broad spectrum of anthropogenic and naturally occurring compounds found in wastewater, including dyes, phenols, pharmaceuticals, petrochemical derivatives, humic substances, and organic acids. While the focus is primarily on conventional organic pollutants commonly found in industrial effluents, the review also references treatment efforts related to emerging contaminants, such as endocrine-disrupting compounds (EDCs), pharmaceuticals, and to a limited extent, per- and polyfluoroalkyl substances (PFAS). However, due to the limited number of CECP studies specifically targeting PFAS, their treatment remains outside the core scope of this review. Instead, emphasis is placed on pollutants that have been more extensively studied in continuous EC systems over the past 25 years.”

This addition ensures that readers have a clear understanding of the pollutant categories covered and the rationale for their inclusion.

Comment 3:Recent advancements (past 2-3 years) in water treatment technologies should be incorporated in the introduction to strengthen the literature context.

Response: We appreciate the reviewer’s insightful comment. The Introduction section has been developed to incorporate several recent advancements in water treatment technologies, particularly within the last 2–3 years. Notably, we have discussed emerging applications such as solar-powered electrocoagulation systems [25–27], which represent a sustainable and cost-effective advancement in the field. Additionally, we have included references to advanced oxidation processes (AOPs), membrane technologies, adsorption, and magnetic separation [15, 20], reflecting modern hybrid and integrated treatment strategies. These inclusions were intended to provide context for the growing interest in energy-efficient, combined, and decentralized treatment solutions.

Comment 4: Page 11’s discussion of CEP’s superior chromaticity/turbidity removal versus lower COD/TOC efficiency requires mechanistic explanation, particularly regarding organic molecular stability variations.

Response: We appreciate the reviewer’s thoughtful comment and agree that a mechanistic explanation would enhance the clarity and scientific depth of the discussion. In response, we have inserted the following explanatory paragraph after the section on Page 11 that compares removal efficiencies, specifically where COD/TOC performance is contrasted with chromaticity and turbidity:

“This can be attributed to the differing chemical characteristics and reactivity of the targeted pollutants. Color and turbidity are primarily associated with colloidal particles, suspended solids, and dye molecules, which are readily destabilized and removed via charge neutralization, electro-flotation, and sweep coagulation mechanisms facilitated by EC-generated metal hydroxides. In contrast, COD and TOC represent the total organic load, including stable and soluble low-molecular-mass compounds such as organic acids, alcohols, and surfactants, many of which are non-ionized and less reactive toward coagulation. These molecules may remain in the aqueous phase due to their solubility and chemical stability, making them less susceptible to removal through electrocoagulation alone. Thus, while EC is highly effective for removing particulate and chromophoric pollutants, its efficiency for complete organic carbon removal is inherently limited by molecular structure and solubility.”

This addition provides a mechanistic rationale for the observed differences in removal efficiencies and highlights the influence of pollutant chemistry on EC performance.

Comment 5: Unit standardization is necessary throughout (e.g., reconcile mA/cm² with A/m² usage).

Response:   We appreciate the reviewer’s observation. In response, we have carefully reviewed and standardized all units throughout the manuscript to ensure consistency and clarity. All unit expressions now align with SI unit standards and have been applied consistently across tables, figures, and text.

Comment 6: Mathematical expressions require consistent italicization of physical quantity symbols per standard conventions.

Response: We thank the reviewer for this helpful comment. The formatting of all mathematical expressions has been thoroughly reviewed, and consistent italicization of all physical quantity symbols has been applied throughout the manuscript in accordance with standard scientific and typographical conventions.

Comment 7: The current reference list appears disproportionately weighted toward the Al-Qodah research group. A more balanced citation approach incorporating contrasting viewpoints would strengthen scholarly rigor.

Response: We appreciate the reviewer’s insight regarding the reference distribution. It is worth noting that Professor Al-Qodah and his research groups have been extensively involved in the field of electrocoagulation (EC) for over two decades, contributing more than 40 peer-reviewed publications (received high number of citations), including both experimental studies (batch and continuous modes) and comprehensive review articles. Their work covers a wide range of topics, including reactor design, modeling, optimization, and combined treatment systems. Consequently, several of their studies were referenced due to their direct relevance to the scope of this review. However, we recognize the importance of maintaining a balanced scholarly perspective that we consider in this review manuscript.

Comment 8: The conclusion section should expand to address key technical challenges, including but not limited to electrode passivation mechanisms and sludge management constraints.

Response: We thank the reviewer for this valuable suggestion. In response, we have substantially revised and expanded Section 8: Concluding Remarks and Future Research Perspectives to explicitly address key technical challenges that hinder the broader implementation of continuous electrocoagulation processes (CECPs). The revised section now includes a detailed discussion on electrode passivation mechanisms, highlighting their causes, operational impacts, and potential mitigation strategies such as self-cleaning electrodes and alternating current operation. Additionally, we have elaborated on sludge management constraints, including sludge separation, handling, and valorization. These additions are intended to provide a more comprehensive overview of the technical limitations and guide future research directions in this field. The revised section also includes appropriate references to support the discussion.

The new writing Section 8: Concluding Remarks and Future Research Perspectives will be as follows:

Continuous electrocoagulation processes (CECPs) represent a promising and evolving technology for the treatment of wastewater contaminated with organic pollutants. This review has demonstrated that both standalone and combined CECPs have achieved high removal efficiencies for a wide range of pollutants, including color, turbidity, COD, TOC, and TSS [3, 25, 28, 58–61]. Furthermore, the integration of CECPs with complementary processes—such as adsorption, biological treatment, and advanced oxidation—enhances overall system performance and broadens the scope of applications [25, 65, 68, 76]. Innovations in reactor design, electrode configurations, and statistical modeling have further advanced the process efficiency and cost-effectiveness of CECPs [35, 36, 50, 57].

Despite these advancements, several technical challenges continue to hinder the scalability and long-term sustainability of CECPs:

• Electrode Passivation: One of the most significant operational barriers is the passivation of electrodes, which occurs due to the deposition of inorganic scales or precipitated coagulants on the electrode surface [36, 39, 50]. This phenomenon reduces the effective electrochemical surface area, increases energy consumption, and compromises pollutant removal efficiency. Addressing this issue requires a better understanding of the chemical and electrochemical mechanisms of passivation under different wastewater conditions. Future research should focus on:
  • Developing anti-fouling electrode materials and coatings;
  • Investigating the use of alternating current (AC) or pulse current modes to minimize passive layer buildup;
  • Designing self-cleaning or rotating electrode systems that promote turbulence and reduce scale accumulation [36, 39];
  • Applying online monitoring and control strategies to detect and mitigate passivation in real-time.
• Sludge Management Constraints: Although EC generally produces less sludge than chemical coagulation, the nature of the sludge—rich in metal hydroxides and adsorbed organics—makes it difficult to handle and dispose of [34, 50, 60]. Moreover, in continuous systems, the accumulation of sludge can interfere with flow dynamics and electrode accessibility. To improve the sustainability of CECPs, future research should explore:
  • Efficient sludge separation techniques, such as electro-flotation and gravity-assisted settling [46, 50];
  • Valorization of EC sludge through resource recovery (e.g., phosphorus, metals) or conversion into construction materials;
  • Real-time monitoring of sludge characteristics to optimize operating parameters dynamically;
  • Hybrid reactor designs that integrate sludge management modules directly into the EC process.
• System Scaling and Standardization: Most CECP studies remain at the lab or pilot scale. Scaling these systems to industrial applications requires addressing issues related to uniform current distribution, flow optimization, heat management, and long-term system stability [25, 60, 66]. Standardizing reactor design and establishing scale-up protocols will be essential for commercialization.
• Process Optimization and Automation: The application of statistical tools like RSM and emerging artificial intelligence (AI) techniques for predictive modeling and control optimization remains limited [35, 38, 57, 60]. Expanding these tools will allow operators to adapt EC systems to variable wastewater compositions and operational conditions, thereby improving robustness and reliability.
• Energy Efficiency and Sustainability: Although solar-powered EC systems have shown promise, more work is needed to improve the energy efficiency of both standalone and hybrid CECPs [25, 28, 50]. Lifecycle assessment (LCA) and cost-benefit analyses are also essential to demonstrate the environmental and economic viability of CECPs relative to conventional treatment technologies.

Based on the challenges identified, the following directions are recommended for future research:

1. Develop and validate novel electrode materials and geometries that resist passivation and reduce maintenance frequency [36, 39].
2. Investigate integrated process configurations that combine EC with sludge minimization and reuse strategies [25, 50].
3. Advance reactor automation and digitalization, including sensor-based monitoring and AI-driven control systems [60, 66, 76].
4. Conduct comprehensive scale-up studies under real-world operating conditions to evaluate reliability, cost, and environmental impact [25, 60].
5. Establish international guidelines and performance standards for continuous EC reactor design, operation, and maintenance.
6. Promote interdisciplinary research combining electrochemistry, fluid dynamics, materials science, and environmental engineering to holistically enhance CECPs.

In conclusion, while CECPs are a highly promising treatment technology for a broad spectrum of organic pollutants, overcoming the challenges of electrode passivation, sludge handling, and scalability is crucial for their full-scale implementation. Future research, guided by a systems-based and innovation-driven approach, will be essential to unlock the full potential of this environmentally sustainable technology.

Comment 9: Manuscript requires thorough proofreading to resolve formatting irregularities (e.g., character encoding issues) prior to publication.

Response:We appreciate the reviewer’s observation. A thorough proofreading of the manuscript has been conducted to correct formatting inconsistencies, resolve character encoding issues, and ensure overall clarity and consistency. We have carefully reviewed the entire document to enhance its readability and ensure it meets the publication standards

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Comment 1: Given the large number of abbreviations used in the manuscript, it would be preferable to provide a separate list of abbreviations, to avoid redundancy and improve readability. 

Comment 2: The quality of Figure 3 needs revision with clear and high resolution images in such a way that the reader can easily read the written portion in these figures.

Author Response

Responses to the Reviewers

 

Dear Editor

We highly appreciate your efforts in leading this esteemed high quality and recognized journal. We would like also to thank the five reviewers who have given deep intention and provide us with constructive comments. Fortunately, we found that for of them were satisfied by our first revision. In addition, Reviewer 2 sent us two constructive comments, which we considered and the manuscript is revised accordingly. We hope that you will find that it is now suitable for publication.     

Responses to Reviewer 2

Comment 1: Given the large number of abbreviations used in the manuscript, it would be preferable to provide a separate list of abbreviations, to avoid redundancy and improve readability.

Response 1 : Thank you for this important comment. A separate list of abbreviations is now added at the end of the manuscript before the references.

 

Comment 2: The quality of Figure 3 needs revision with clear and high resolution images in such a way that the reader can easily read the written portion in these figures.

Response 2 : Thank you for this important comment. The quality of Figure 3 is improved.

Reviewer 3 Report

Comments and Suggestions for Authors

Authors have addressed all the comments and questions. 

Author Response

Thank you for accepting our responses to you constructive comments  

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have responded sufficiently to the comments.

Author Response

Thank you for accepting our responses to you constructive comments  

Reviewer 5 Report

Comments and Suggestions for Authors

could be accepted now.

Author Response

Thank you for accepting our responses to you constructive comments