Technological Parameters of Rotating Electrochemical and Electrobiological Disk Contactors Depending on the Effluent Quality Requirements

Round 1

Reviewer 1 Report

Good day! 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 1,

Thank You very much for Your comments.

These are our answers:

 

1. Line 16 - the abbreviation RECDC does not match the definition. Line 37 - In Keywords, I propose to add the abbreviations RECDC and REBDC. The Introduction should explain more precisely what is the difference between RECDC and REBDC.

The abbreviations RECDC and REBDC have been completed in Abstract and Keywords.

 

2. In the Materials and Methods section, I propose to present the composition of the initial synthetic water. It is not clear from which components the model solution was made.

The table with the composition of the synthetic wastewater has been added.

 

3. Table 2 does not present the initial parameters (before treatment), so it is difficult to judge the effectiveness of cleaning.

Denitrification is the process of converting nitrites and nitrates into their simplest constituents. Those. in the process of denitrification, the content of nitrites and nitrates should decrease. The abstract says that the highest denitrification effect occurs at electric current density 10 A/m2 and HRT=24h. This is contradicted by the results presented in Table 2 for Nitrite. These results generally diverge from others in Nitrites by hundreds of times, which casts doubt on the results.

I think that in Table 2 it is necessary to provide information on the concentration of phosphorus, and also to explain what kind of phosphorus is meant: total phosphorus or phosphate phosphorus.

Table “Quality of wastewater treated in RECDC and in REBDC – mean values” was supplemented with concentrations of total nitrogen, nitrates and total phosphorus as well as parameters of wastewater flowing to RECDC and REBDC. During the flow of an electric current with a density of 10 A/m² and HRT=24h the concentration of nitrites increased, but at the same time the concentration of nitrates decreased significantly. I hope that now, thanks to the reviewer's suggestion to complete the table, it is more understandable.

 

4. In Figures 2a, 2b, 3a, 3b it is not clear what is meant by APre and ANre. It is necessary to explain in the text or give a decoding on the graph. This remark applies to Figures 4 and 5 for the naming of the y-axis.

The y axis designation in figures 2-5 is explained.

 

5. The low value of R² (in Figure 2a) for HRT=8 and HRT=24. Although visually the experimental points are practically on a straight line. This question also applies to Figure 3a, with HRT=12 and HRT=24; and Figure 4 and 5a.

According to the statistical interpretation of the results, the value of R², within the following ranges, means:

0.5 - 0.6 - weak fit

0.6 - 0.8 - satisfactory fit

0.8 - 0.9 - good fit

0.9 - 1.0 - very good fit

In most cases, R² was above 0.9, which means a very good fit. For some dependencies, it was from 0.8 to 0.9, which means a good fit. In a few cases it was in the range of 0.6-0.8, which means a satisfactory fit. Only in two cases was the coefficient in the range of 0.5-0.6, which means a weak fit. In the case of Figure 3a, the L^AP_re values were: 5.72, 5.91, 5.93, 5.91 and 5.92, for J=0.63; 1.25; 2.5; 5.0 and 10.0 A/m², respectively and HRT=24 h. Although visually the experimental points are practically on a straight line, from statistical point of view it is a weak fit.

 

6. The Figures 6 and 7 - require the graphical correction.

The figures 6 – 8 have been corrected.

 

7. The question also arises about the volume, accumulation and disposal of excess biofilm, which is formed as a result of reproduction in RECDC and REBDC.

We fully agree with the Reviewer's opinion. We hope that the sludge (excess biofilm) from both reactors can be used in agriculture as a source of nutrients. As You noticed we presented the sludge management procedure in Fig. 7 and 8. Our research showed that the sludge doesn’t contain too much organic substances so it may not need a stabilization process. But we are preparing now a separate publication will be devoted to sludge from both reactors – their quantities and characteristics.

In our previous article on the treatment of wastewater from soilless tomato cultivation in an anaerobic bio-electrochemical reactor using an alternating current, we presented the data of sewage sludge (Bryszewski, K.Ł.; Rodziewicz, J.; Mielcarek, A.; Janczukowicz, W.; Jóźwiakowski, K. Investigation on the improved electrochemical and bio-electrochemical treatment processes of soilless cultivation drainage (SCD). Sci. Total Environ. 2021, 783, 146846. doi.org/10.1016/j.scitotenv.2021.146846).

 

8. The discussion did not address the issue of introducing pesticides into wastewater that are used to kill pests at certain times. And how these pesticides can affect bacteria in reactors.

During the research, we used synthetic wastewater with a composition corresponding to the wastewater from greenhouses on a technical scale, with which we cooperate. No pesticides were used on any of them, biological protection is carried out in accordance with the biological protection program, or diseased plants are removed and some of the greenhouses are excluded from production. Therefore, we did not deal with pesticides in our research.

 

9. I think the Results and discussion section should be shortened with respect to the description of the figures. The presented schemes (Figures 6,7 and 8) are not compared in terms of economic costs; the shortcomings of the schemes are not considered.

 

We shortened this section according to Your suggestion and added information about costs and shortcomings.

 

 

10. There are no unresolved issues or research opportunities in this section.

We have added an excerpt on unresolved technological issues and the subject of further research.

 

11. Line 667 - This conclusion is inaccurate as the results of the studies do not demonstrate the dependence of reactor efficiency on wastewater temperature.

 

In table 3 (previously 2) we can find information about the temperature of wastewater in the reactors during the treatment process. As the current density increases, it increases. At the current density of 10.0 A/m², in electrochemical and electrobiological reactors the temperature of the wastewater exceeded 35 ° C. The treated wastewater with a temperature of 35^o C cannot be discharged to the sewage system or to natural receivers (table 2, previously 1).

 

12. In my opinion, the Conclusions should be substantially improved and reduced.

 

The Conclusions section has been corrected and shortened

 

 

The manuscript has been revised according to the Reviewers' comments and all revisions in paper, made by authors, are highlighted using the "Track Changes" function in Microsoft Word.

Dear Reviewer 1

Thank you very much for Your comments.

Author Response File: Author Response.docx

Reviewer 2 Report

The study results presented in this manuscript demonstrate that the soilless tomato cultivation wastewater can be treated in both electrochemical and electrobiological disk contactors and afterward discharged to municipal sewerage facilities.

1. The description of introduction and conclusions sections was too long, authors need to focus on the progress about the wastewater treatment, especially for low COD. Furthermore, advise authors to summarize the gap and application for electrochemical and electrobiological approaches to treat the similar wastewaters.
2. The title of this manuscript is too long, advise authors to shorten it based on the novelty or topic of study.
3. Some expression need be consistent. For example, Table 1 and Table 2, N forms and so on.
4. Electric dissolution of the aluminum anode and the dissolution of contactor case and disks made of steel resulted in the formation of aluminum and iron ions, although the presence of two ions had little influence on the effluent discharge, the electrode was damaged gradually.
5. Advise authors to divide the full text into some subsections or subtitles, in order to express clearly on the logical and contents.

Author Response

Dear Reviewer 2,

Thank You very much for Your comments.

These are our answers:

The study results presented in this manuscript demonstrate that the soilless tomato cultivation wastewater can be treated in both electrochemical and electrobiological disk contactors and afterward discharged to municipal sewerage facilities.

1. The description of introduction and conclusions sections was too long, authors need to focus on the progress about the wastewater treatment, especially for low COD. Furthermore, advise authors to summarize the gap and application for electrochemical and electrobiological approaches to treat the similar wastewaters.

Introduction and Conclusion sections were shortened and corrected.

 

1. The title of this manuscript is too long, advise authors to shorten it based on the novelty or topic of study.

The title of the manuscript was shortened.

 

1. Some expression need be consistent. For example, Table 1 and Table 2, N forms and so on.

Expressions were standardized.

 

1. Electric dissolution of the aluminum anode and the dissolution of contactor case and disks made of steel resulted in the formation of aluminum and iron ions, although the presence of two ions had little influence on the effluent discharge, the electrode was damaged gradually.

The aluminium electrode, which is anode, is electrolytically dissolved. Because the process of dissolution takes a long time, it is only after some time that the anode will be replaced with a new one.

1. Advise authors to divide the full text into some subsections or subtitles, in order to express clearly on the logical and contents.

The section “Results and discussion” has been divided into subsections.

The manuscript has been revised according to the Reviewers' comments and all revisions in paper, made by authors, are highlighted using the "Track Changes" function in Microsoft Word.

Dear Reviewer 2

Thank you very much for Your comments.

Author Response File: Author Response.docx