Study on the Interaction between the Reduction and Remediation of Dredged Sediments from Tai Lake Based on Vacuum Electro-Osmosis

Round 1

Reviewer 1 Report

In this manuscript, based on a detachable vacuum electro-osmotic indoor model experiment system, dredged sediment from Tai Lake is used to conduct vacuum, electro-osmosis and vacuum electro-osmosis reduction and remediation experiments with and without cooper contamination. Results show that copper contamination weakens the effect of reduction, and the production of copper precipitates makes the soil more prone to cracking and blocking rainage channels, which has the greatest impact on the electro-osmosis method. In terms of copper concentration, vacuum electro-osmosis combined the advantages of both to achieve the transport and discharge of contaminants, and has the best remediation effect. The removal rates at the anode and cathode are 45.1% and 50.0%, respectively. A correlation model based on electrical conductivity, moisture content and contaminant concentration is established to facilitate the determination of contaminant concentrations in actual projects. Electro-migration plays a dominant role in the remediation process, and the reduction affects the electric field distribution and thus the migration efficiency. 

The research done is interesting and important in solving environmental issues. The course of the experiments is laid out clearly and in detail, the conclusions fully correspond to the results of the experiment.

Author Response

Thank you very much for your recognition of our research work, which is our motivation to continue our efforts.

Reviewer 2 Report

Review of Manuscript ID: applsci-2071344

The reviewed manuscript main issue is effectiveness of remediation of dredged lake sediment sediment, contaminated by copper using vacuum electro-osmosis.

Using electro-migration process theoretically could help to remove certain amounts of heavy metals from dredged sediment. In the case of heavily polluted sediment this procedure shows potential for removing such harmful pollutants.

In spite of fact, that the reviewed manuscript concerns very interesting and important subject, it shows several flaws, which should be explained.

1. Why Authors decided to prepare contaminant sediment with very high copper amounts comparing to non-modified sediment? Whether such high copper contamination is very common in lake sediment? For example the EU standards threshold for Cu is <150 mg/kg, then Cu concentration in prepared sediment is order of magnitude higher. In my opinion lower concentration of Cu, but above of 150 mg/kg could be also tested.

2. Why Authors used not fresh, but dried sediment from Tai Lake for experiment? If sediment is dredged from lake, it will have rather high moisture and it is not necessary to dry it and later use water for obtaining hydration.

3. The structure of manuscript is incomplete. After presenting results is almost completely no discussion of results, just statements and conclusions. It is necessary to compare results with scientific literature. Discussion is necessary in scientific publication. Then I conclude, that manuscript in the present state is incomplete, and it needs to be corrected and expanded.

 

Minor comments:

Line 23 – the word “caly” should be corrected into “clay”

Lines 25, 146, 361, 506 – the word “cooper” should be corrected into “copper”

Line 41 – “ the word “mental” should be corrected into “metal”

Author Response

Thank you very much for your recognition of our research work, which is our motivation to continue our efforts. We will respond to your comments one by one.

1. This is a very detailed issue, and I am very sorry that I did not clarify it in the text, and I have added some words to supplement it in section 2.1. Materials. Due to the continuous discharge of pollutants from sewage treatment plants around lakes, the concentration of pollutants in the sediment is much higher than the general standard. According to China’s Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002), the maximum allowable levels of copper in acidic and non-acidic sediments are 800 and 1500 mg/kg respectively. However, as this part of the sediment is more difficult to obtain in large quantities and it is difficult to ensure the homogeneity of the contaminant distribution inside the sediment, which is not conducive to controlling variables and reflecting experimental patterns. This study focuses on the combined effect of consolidation and remediation under vacuum electro-osmosis, while the initial inhomogeneous distribution of contaminants within the specimen can affect the test results. At the same time, higher concentrations of copper can also better enlarge the effect of changes in contaminants on consolidation. Consequently, this study adopts the way of preparing high concentration contaminated soil samples within the laboratory, which is both closer to the reality and can reflect the experimental laws well. Certainly, the concentration of 150 mg/kg can also be tested, and the effect of different concentrations is also a direction worth studying.
2. Again, this is a matter of great detail. Since the location of the sample collection and the laboratory were not in the same city, the freshly excavated sediment had evaporated a lot of moisture by the time it was transported to the laboratory, which could lead to inconsistency between the test soil samples and the field conditions. On the other hand, since the soil samples were excavated from the lake site, they were interspersed with stones, water plants, shells and other impurities, which needed to be dried, crushed and ground to remove the impurities. The tests in this study include not only decontamination but also dehydration and drying, and the presence of impurities also affects the pore condition of soil samples, which in turn leads to uncontrolled dehydration in each set of tests.
3. Thank you very much for your suggestion, we have added a discussion of the results after the conclusion.
4. Thanks very much for all the detailed comments, all issues have been corrected

Reviewer 3 Report

The manuscript, Study on interaction between reduction and remediation of dredged sediment from Tai Lake based on vacuum electro-osmosis, compares three methods for the reduction and remediation of dredged sentiment samples that are either contaminated with copper or not. Of the three methods employed (electro-osmosis, vacuum, and vacuum electro-osmosis) the general consensus is that vacuum electro-osmosis is demonstrates the best remediation effect by combining the separate assets of electro-osmosis and vacuum methods. It is supported by the findings that the presence of copper as a pollutant interferes with the electro-osmosis process. The authors suggest a correlation model that could be useful for determining contaminant concentrations on the basis of electrical conductivity. 

 

Overall, the authors present a very thorough study design. A comparison of the three reduction-remediation methods yield useful information via the use of an indoor scaled model that may be applicable to larger reduction and remediation projects. The authors explain the various phenomena observed (such as the reason for the orientation and prevalence of cracks in dried sediments and variations in conductivity due to decreasing moisture content) and provide a useful model for correlating moisture content, conductivity, and concentrations of contaminants.  The reasoning for the various data sets seems quite sound. 

 

I have some general comments in hopes of clarifying the overall experiment design:

 

For Fig 1, please provide a scale in km on the map so that the area of collection can be put into context. 

 

Please clarify- do the dredged sentiment samples represent uniform (random) collection from the area shown in figure 1? Or are the samples isolated from distinct points within this area? The sediment composition could vary depending on its point of origin, but this may be mitigated if the sediment was collected from different points within the area.

 

What is the n for each study? Were the data sets T1-T6 performed only once or were these experiments performed multiple times? The n for each experiment should be stated. 

 

On a related note, if data sets T1-T6 were replicated as multiple experiments then the data presented in most figures should reflect this by incorporating error bars for measurement. This isn’t necessary if n=1 for each study. 

 

Overall I feel that the manuscript provides a useful set of observations for various forms of reduction-remediation methods on sediments and offers a useful model for predicting copper contamination in dredged sediment.  

Author Response

Thank you for your recognition to our research work, which is our motivation to continue our efforts. We will respond to your comments one by one.

1. A scale in km on the map is provided in Fig 1.
2. The sediment used in this study was taken from the construction site at this location. To ensure that the properties of the test specimens did not vary too much, the soil samples used were all taken from the same location within the same area, rather than selecting different sampling locations. We selected sampling locations where the soil samples had the highest moisture content and their properties were closest to the sediment. The difference in soil sample properties may affect the test if collected from different locations.
3. n=1. Although we actually carried out each set of tests more than once, only one group of full data that could be used for analysis was adopted due to the long test period, during which there was a possibility of air leakage and power failure, and the other attempted tests could only be used for reference. And considering that the soil samples were not enough to carry out many groups, and that the soil samples before and after the test had to undergo many chemical analyses, which was costly. Thus, the n for each study is 1.

Reviewer 4 Report

The authors of the paper entitled “Study on interaction between reduction and remediation of dredged sediment from Tai Lake based on vacuum electro-osmosis” have done good work, integrating the electro-osmosis, vacuum, and vacuum electro-osmosis methods for the remediation of dredged sediment but the manuscript is poorly written and lacks clarity; Their English is very poor to understand what their objective is . Thus, I suggest a major revision with some of my comments provided on the manuscript attached. The authors should clearly define their objective and avoid using confusing comparisons between reduction and remediation. They should say remediation as to how far the reduction in the copper content demonstrates the degree of remediation. They should seek proficient English language writing assistance and rewrite the manuscript contents properly 

Comments for author File: Comments.pdf

Author Response

Thank you for your recognition to our research work, which is our motivation to continue our efforts.

1. Thank you very much for your suggestion, and we are sorry that our poor writing skills have caused you trouble in reading. We have further revised the manuscript and made many changes especially in the English expression. All the issues that you have annotated in the document have been fixed.
2. The object of this study is the reduction and remediation of dredged sediment. Reduction refers to the dewatering and drying of the sediment to reduce its water content while making it smaller in volume and occupying less space when placed in a yard. Remediation refers to reducing the contaminant content of the contaminated sediment so that it no longer poses a continuing environmental hazard when placed in a yard. We have further strengthened the expression in the text so as to avoid confusion in the statement of the study objectives.

Round 2

Reviewer 2 Report

Dear Authors,

In my opinion you made demanded revisions and manuscript was improved. I have no further comments to present version of manuscript.

 

Author Response

Thank you very much for your recognition of our research work, which is our motivation to continue our efforts.

Reviewer 4 Report

The authors of the revised manuscript entitled  "Study on interaction between reduction and remediation of dredged sediment from Tai Lake based on vacuum electro-osmosis" have addressed almost all of my comments. Thus I suggest publication of the paper after minor revision of the manuscript as commented on the manuscript attached. 

Comments for author File: Comments.pdf

Author Response

Thank you very much for your recognition of our research work, which is our motivation to continue our efforts. We have made changes according to your comments on the manuscript attached.