Field Demonstration of In Situ Slow-Release Oxygen Chemicals Coupled with Microbial Agents for Injection to Remediate BTEX Contamination

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

I appreciate authors to present their study on Field demonstration of in situ slow-release oxygen chemicals coupled with microbial agents for injection to remediate BTEX contamination. I have following recommendations to improve the article to be published in this reputed journal.

1.  Authors have demonstrated that slow release oxygen chemicals coupled with microbial agents can reduce BTEX in groundwater.

2. Authors must introduce abbreviation on its first use. For example- BTEX didn't introduced.

3. How these organic chemicals were measured is not explained in method.

4. The representation of method can be done with a flow chart in material and methods section.

5. As study has been done in field, a proper study area map could be provided, indicating country/province, state and location.

6. Why 6 dats before the level of BTEX is higher than 1 day  before injection. If so, authors should use atleast three seasons samples to understand the range of BTEX in growndwater. 

7. English needs to be improved throughout the manuscript. There are issues in connection of sentences, I suggest authors to go through entire text and rewrite.

8. Results could be discussed better by comparing this study to others. Results from few lab based experiments can be provided (in case there are few or no similar studies on Field). 

9. Graphs can be changed with different patterns, for better understanding and representation of data.

Overall,this manuscript needs a lot of improvement to achieve the standard of publication in good journal,I suggest authors to rework on it and rewrite where ever corrections are needed.

 

Comments on the Quality of English Language

English needs to be improved 

Author Response

Comments 1：Authors have demonstrated that slow release oxygen chemicals coupled with microbial agents can reduce BTEX in groundwater.

Response 1: We agree with this comment. We demonstrate this through field experiments.

Comments 2: Authors must introduce abbreviation on its first use. For example- BTEX didn't introduced.

Response 2: Thank you for pointing this out.  We have added full names to abbreviations in the manuscript. This change can bu found in line 27,56,95,159.

Comments 3: How these organic chemicals were measured is not explained in method.

Response 3: We have supplemented the detection method in page 5.

Comments 4: The representation of method can be done with a flow chart in material and methods section.

Response 4: Since our experiments mainly take place in the actual field, we have described the existing methods in the second part, and we can provide more reliable information if needed.

Comments 5: As study has been done in field, a proper study area map could be provided, indicating country/province, state and location.

Response 5: The location information of the site is confidential of the company, which is related to national energy security. We are sorry that we cannot provide the exact location, but we have provided the approximate location information in line 110.

Comments 6: Why 6 dats before the level of BTEX is higher than 1 day  before injection. If so, authors should use atleast three seasons samples to understand the range of BTEX in growndwater. 

Response 6: The pollutant concentration in groundwater fluctuates to a certain extent due to sampling or weather and other reasons. We measured the pollutant concentration 7 days before the experiment and 1 day before the experiment, and the level was basically the same, shown in Fig. 5.

Comments 7: English needs to be improved throughout the manuscript. There are issues in connection of sentences, I suggest authors to go through entire text and rewrite.

Response 7:  Thank you for pointing this out. l agree with this comment. Therefore, we have checked and improved the English of the full text.

Comments 8:  Results could be discussed better by comparing this study to others. Results from few lab based experiments can be provided (in case there are few or no similar studies on Field)

Response 8: We designed a pollution control scheme according to the pollution status of the specific site, and tried to eliminate the pollution by using self-developed or commercial bacteria agents. The test process of self-developed bacteria agent is completed by colleagues, which involves certain commercial secrets, and I have no right to disclose more information.

Comments 9: Graphs can be changed with different patterns, for better understanding and representation of data.

Response 9:  This article is a report of a relatively rare field trial. It is difficult to present graphs with more regularity than lab work. In order to visually display the experimental process and experimental results, we adopt a similar processing style. We can modify specific drawings if necessary.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript is written well and contains important results. The interpretation of the results is good. The manuscript can be published after minor revisions.

The novelty of this study must be highlighted in the introduction and the reason for selecting BTEX and microbial agents must be mentioned.

The figures drawn by the Excel Software are simple and need to be modified. 

Figure 7 is not required and must be removed.

A comparison of results with previous studies is necessary.

Comments on the Quality of English Language

The English are acceptable.

Author Response

Comments 1: The novelty of this study must be highlighted in the introduction and the reason for selecting BTEX and microbial agents must be mentioned.

Response 1: We agree with this comment. Therefore,  we have add the novelty of this study and provide the reasons for choosing the combination injection of slow release agents and microbial agents in Introduction.

Comments 2:  The figures drawn by the Excel Software are simple and need to be modified. Figure 7 is not required and must be removed.

Response 2: Thank you for pointing this out. We adapted the figures in the paper. The images that could not show more effective information were deleted, and some images were optimized.

Comments 3:  A comparison of results with previous studies is necessary.

Response 3:  Agree.  We have add a comparison of results at the end of the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

 

Review of the manuscript water-3209221:

In this manuscript, Yang et al. demonstrate the on-site application of biostimulation and bioaugmentation technologies for the enhanced remediation of a BTEX-contaminated field at the Mao Wusu desert in northwest China. Biostimulation is applied through the injection of materials that slowly release oxygen and facilitate the aerobic biodegradation of BTEX. Bioaugmentation is applied through the injection of pre-adapted bacterial species. Overall, the study is well designed, the results are interesting, and the manuscript is quite well written. Although I cannot recommend acceptance in the present form, I strongly encourage the authors to consider the comments given below and revise their manuscript accordingly. 

Technical comment

My main concern is the estimation of the reference BTEX concentration on and beyond the 20th day, after a side plume invaded into the test area and caused a significant increase in BTEX concentrations. First of all, some minimum information is needed about the source of the contaminant plume. For instance, the release of contaminated wastewater from the nearby refinery plant was scheduled or occurred accidentally? Are there any data about the frequency of wastewater discharge and the distance from the test area?

            Furthermore, the idea of the authors to estimate new reference values, based on ratio analysis and modelling, is smart. However, the BTEX concentrations estimated from the two approaches show significant differences. For example, the estimated BTEX concentration in J10 well is 4644.36 mg/L from ratio analysis (Table 2) and, almost double, 7952.25 mg/L from numerical simulation (Table 3). How is this significant discrepancy explained? Which approach is considered as more reliable?

 

Editorial comments

1. L15: The words "could be" are not needed.  

2. L17: Perhaps, the term "self-developed" could be replaced by the term "pre-adapted", which conveys more clearly the fact that these bacteria were acclimatized to hydrocarbon degradation at soil temperature.  

3. L21: Remove the duplicate phrase "The research results provided". 

4. L31: Replace "will cause" with "causes". 

5. L47: The statement "is also a hot topic" is somewhat informal for a research paper. Perhaps, could be replaced by "has also received significant attention". 

6. L61-62: As written, this statement is vague because the "many differences" between lab-scale and field-scale experiments are not defined. Perhaps, instead of focusing on the differences, the authors could focus on the complementarity of experiments at different scales by replacing this vague statement with something like: "Groundwater and soil contamination is a multiscale process and the development of efficient remediation technologies requires research across multiple spatial and temporal scales (Li et al., 2017). Microscale experiments under well-controlled and reproducible setups provide fundamental insight into the mechanisms and optimal conditions of biodegradation (Kapellos, 2017). However, the transition from laboratory to pilot-scale and, ultimately, to the field scale remains challenging as greater uncertainties exist under real-world conditions (Scammacca et al., 2023)."  

7. L63-65: The paper by Ellis et al. (2000) presents a landmark study on the successful demonstration of field-scale bioremediation of soil contaminated by trichloroethene (TCE) through the coupled injection of chemical and microbial agents. I strongly recommend to add this citation in line 65 along with ref 23.  

8. L74: Replace "fine" with "define".

9. L76: The term "bactericide" seems to be misused (appears also in lines 145 and 146). Perhaps, the authors simply mean "bacteria".

10. L80-83: Cite the previous research papers on which this work builds.

11. L94-98: Provide information about the source (e.g., supplier and product number) of the calcium peroxide powder.

12. L100-104: Cite the reference for the isolation and characterization of the indigenous bacteria.

13. L105: Please check the spelling of the supplier name and provide the product number for the commercial bacteria.

14. L100-107: Are these bacteria chemotactic to BTEX?

15. L110: Replace "gentle" with "flat".

16. L111-113: Are there data from the lithological analysis for the grain size of the sand?

17. L158: Please define the term MIP (membrane interface probe).

18. L161: Correct "wae" by "was".

19. L162: The BTEX concentrations presented in Figures 4, 5 and 11 correspond to a specific depth or represent depth-averaged values?

20. L187: Please clarify whether the activation matrix alginate or some other polymer?

21. L197: The term "bacteriophage" is misused (also in lines 199, 201, 301, 315).

22. L254 and L256: Replace the vague term "Hydrogeochemical indicators" with "Dissolved oxygen concentration".

23. L281: In Figure 10, for groups 3 and 4, which bacterial species were abundant? In the literature, many Pseudomonas species play a critical role in the biodegradation of aliphatic and (poly-) aromatic hydrocarbons (e.g., Table 1 in Kapellos, 2016). Did the authors detect any Pseudomonas species in their genomic analyses of soil samples?

24. L281: In Figure 10, for group 4, the small rise in the abundance of Bacillus at the 90th day may be attributed to transformation of the local bacterial community or lateral migration of bacteria from the injection point close to the J7 well?

25. L285-287: Usually, turbulence is very weak in porous media. Instead, is it possible that the rise in the contaminant concentration could be attributed to enhanced desorption caused by the pressure pulse?

26. L335 and L345: In the literature, the term "degradation rate" typically represents the mass of degraded contaminant per mass (or volume) of soil and per unit time. The percentage of biodegraded BTEX represents the degradation efficiency. Please check the correct use of the term "degradation rate".

27. L337: Please define the acronym "GSM" and cite the paper with details on the numerical simulation of BTEX transport.

28. L353: Please specify whether the results in Figure 12 were calculated with the ratio analysis or the numerical simulation.

 

Suggested references

[1] D.E. Ellis et al., Bioaugmentation for accelerated in situ anaerobic bioremediation, Environmental Science & Technology, 34 (2000) 2254-60. https://doi.org/10.1021/es990638e

[2] G.E. Kapellos, Microbial strategies for oil biodegradation, Modeling of Microscale Transport in Biological Processes, Cambridge, MA: Academic Press, (2017) 19-39. https://doi.org/10.1016/B978-0-12-804595-4.00002-X

[3] L. Li et al., Expanding the role of reactive transport models in critical zone processes, Earth-Science Reviews, 165 (2017) 280-301. https://doi.org/10.1016/j.earscirev.2016.09.001

[4] O. Scammacca et al., Effect of spatial scale of soil data on estimates of soil ecosystem services: Case study in 100 km2 area in France, European Journal of Soil Science, 74 (2023) e13359. https://doi.org/10.1111/ejss.13359

Comments on the Quality of English Language

Please see the list of editorial comments.

Author Response

Comments 1: For instance, the release of contaminated wastewater from the nearby refinery plant was scheduled or occurred accidentally? Are there any data about the frequency of wastewater discharge and the distance from the test area?

Response 1: The release of contaminated wastewater from the nearby refinery plant was occurred accidentally.It was a short-lived process bug that was fixed by the company. We reported it to the company and fixed it. It was not clear at the time of the discovery that it would affect the results of the experiment so the sewage was not sampled and analyzed, so we don't have any information about it.

Comments 2: How is this significant discrepancy explained? Which approach is considered as more reliable? We can't say which method is more accurate because the actual data is missing.

Response 2: These two methods are to demonstrate the effectiveness of the combination of slow release agents and bacterial agents. However, these two methods indicate a common result that the combined injection can effectively control the low level of BTEX contamination in the site to some extent. This provides important support for enterprises to carry out production and control work in the later stage.

Comments 3: I strongly encourage the authors to consider the comments given below and revise their manuscript accordingly. 

Response 3: Many thanks to the reviewers for their nuanced comments. All suggestions were accepted and modified. A deeper understanding of the study was gained in the process. Thanks again to the reviewers for their efforts to improve this paper.