Comparison of Online Sensors for Liquid Phase Hydrogen Sulphide Monitoring in Sewer Systems
Round 1
Reviewer 1 Report
The article “Comparison of Online Sensors for Liquid Phase Hydrogen Sulphide Monitoring in Sewer Systems” is interesting and suitable for publication. I believe my detailed comments will be useful.
Analyzing the aim of the research it is difficult to find out “scientific problem”, however presented research has a great practical value.
At the end of “introduction “ chapter please write clearly what was the reason to carry on research with chosen sensors - comparing, in my opinion, is not enough.
Chapter 2.2 (line7)
Avoid such a term as “trials”, please replace it.
??2- please explain this parameter
Chapter 2.4 line 8 and figure 1
What kind of chemicals do you mean?
Chapter 2.5 line 11
“All samples were measured within 2-3 days from the date of sampling”- please explain it.
Results
What was the range of pH?
Page 9
What does it mean “local calibration” ?
Chapter 3.3
For the applied nitrate dosages of 7.5 (limited), 14 (optimal), and 28 mg-N L-1
What it means “limited” and “optimal”?
“Under the nitrate dosing trials, an increase in the sewage pH ranging from 0.7 to 1.3 pH units was measured for the different dosing scenarios—a median pH of 7.1 without dosing compared to a median of pH 8.4 during the overdosing”.
In my opinion there is no such a term as median or mean pH.
Chapter 3.5, table 2.
The most interesting and valuable part of your article from practical point of view.
Conclusions
Please extend this chapter with some detailed results from chapter “results and discussion”.
Author Response
Dear Reviewer,
We thank you for reviewing our manuscript and providing insightful feedback. We revised the manuscript according to your suggestions and points raised.
Please see the attached pdf file for our responses to your comments.
Kind regards,
The Authors
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript reports on the comparison of three market-ready online sensors (two optical sensors based on UV-Vis spectrophotometry and one Clark-type electrochemical sensor) for liquid-phase hydrogen sulfide (H2S) detection in sewer systems, which is important in order to devise control measures concerning wastewater management in sewer systems. The three sensors were gauged against a standard laboratory method and then they were evaluated under different but realistic sewer conditions. The pros and cons of each sensor for liquid-phase H2S detection were discussed.
The manuscript is suitable for publication, however some minor issues concerning the English text have to be previously addressed:
- “the H2S Analyser Cubi…” (Section 2.1. Sensors) vs. “the H2S Analyzer Cubi…” (Section 2.5. Sampling, Laboratory Analysis, and Data Collection).
- Page 9: “… one must consider the possible errors during sampling, sample preparation, and measurement. For example, during the sample perseveration (preparation???), we only used zinc acetate”
- Section 3.3 Performance of Sensors During Nitrate Dosing
Figure 5(a-c) displays the hydrogen sulfide (H2S) profiles obtained during nitrate dosing. For the applied nitrate dosages of 7.5 SPACE (limited), 14 SPACE (optimal), and 28 mg-N L-1 SPACE (over-dosing),
- Page 12: “the sample absorption spectra are a superposition of the absorption spectra of several species, deconvolution is required to identify and differentiate the different species [7].
In comparison, the global calibration of OPUS followed the semi-deterministic devolution (deconvolution???) procedure in which a linear substance analysis (curve-fitting) and multiple linear regression analysis…”
- Page 12: “The SulfiLoggerTM requires no specific data prepossessing ??? and cumbersome calibration routines as the H2S detection relies on the…”
- Page 14, first line: “as pH elevation (e.g., Magnesium Hydroxide),” magnesium hydroxide.
- Table 2, ISA advantages: “Measurement quality details SPACE (Spectral Quality Index)”
- Supporting Information: Section 1.4. H2S removal percentages “Calcuation CALCULATION of the H2S removal percentages”
Author Response
Dear Reviewer,
Many thanks for your feedback and points concerning the text. We have revised the manuscript and corrected it accordingly. Please see the attached.
Many thanks,
The Authors
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors,
the manuscript entitled “Comparison of Online Sensors for Liquid Phase Hydrogen Sulphide Monitoring in Sewer Systems” (ID water-1262772) is good planned and clearly described. I find your work very well. The manuscript is prepared carefully. The article describes very important issues concerning the accurate and reliable measurements of hydrogen sulphide forms in environmental samples. I know this topic very well, mainly from laboratory work in the area of technological processes of groundwater.
I have got some minor comments presented below. These are suggestions, not requirements.
- I propose to add information about manufacturers' recommendations on the topic:
- conditions of liquids for sensors applications (optimal and not recommended)
- operating ranges and sensitivity and precision in each range.
+ Prove whether the conditions of the experiment meet these requirements in each case.
++The main information (also from paragraph 2.1.) could be in the table for easy comparing. Also, the type of measured sulphide species is here needed. I know, it is in paragraph 2.3., but the reader thinks about it already when reading about the sensors’ characteristic.
- I feel a lack in the first step of methodology. The Authors compared the measurement using sensors with the reference method. In my opinion, it should be arranged the same, but when the model solution was analysed. The model solution I understand like synthetic wastewater (manually prepared) containing hydrogen sulphides species typically occurred in sewer systems (according to pH). This could be a few comparative experiments for these methods under different pH conditions and thus the presence of H2S/HS-/S2- forms. I can see it when a clean solution is used and also a solution with organic matrices, N, P and others components representative for wastewater, but in controlled concentration and known composition. It could give the base comparison between methods in a controlled system. If such research has already been done, I suggest that you specify it more clearly
- Can the measured values of ORP be included in the comparative analysis? You inform about measuring but not presenting the results and not discussing them.
- The penultimate line in paragraph 2.3. - pKa2 occurs twice.
Best regards,
the reviewer
Author Response
Dear Reviewer,
Many thanks for your fruitful and insightful feedback. We tried our best to modify the manuscript according to your suggestions.
Please see the attached responses.
Kind regards,
The Authors
Author Response File: Author Response.pdf
