Automated Monitoring of a High-Speed Flocculation Flat-Bottomed Sludge Blanket Clarifier Pond during Drought and Flood Conditions

Round 1

Reviewer 1 Report

1. This paper describes an automated multi-layer sensor based on conductivity and electrodes for sludge blanket thickness measurement in a high speed flocculation flat bottom sludge blanket clarifier (HFSBC) used in water treatment plants mainly to cope with high water quality changes to the plant. This a paper with practical consequences. 

The introduction is well covered and based on relatively new papers as reference.

2. My first objection will be the lack of a clear flow sheet of the system depicting the multi-layer sensor and HFSBC (a detailed description is OK but the advantage of a well drawn flowsheet or picture is obvious).

The multi-layer sensor which measures relative conductivity and the thickness electrodes system is described as R-EC as compared to the absolute conductivity measurements. 

I also have to mention that in the past similar processes have been conducted by means of an on-line-PSD analyzer which gave particle density with two probes, before and after the Sludge blanket and thickness measurement. As it is in the paper in that case too the measurement of the particle density is known indirectly but is very accurate. The system was directly connected to coagulant addition system to maximize the HFSBC operation as also described in the paper.

3. I understand that when the authors mention that the entrance is from the bottom and the sludge is evacuated in a region formed by the conus at the entrance area and the RPMS was installed at 2m. from the entrance.

All this as said before is very hard to figure so again a very clear schematic system explaining all what is written in this part of the paper would be much clearer and also save space by briefly explaining on the flowsheet the main parameters and heights. This would improve the "Materials and methods" part.

4. Also I think that, to say "the sludge blanket will be from 2-5m. (3 m. high)" is a bit risky for the overflow channel, and the upper region must be maintained few cm. free of any sludge or particles.  So if the HSFSBC total height is 5m., the sludge blanket (depending on the flow velocity) can be up to 10-20 cm. lower to take into account the sudden flow changes.

5. In the "Materials and methods" there is no mention of the flocculant PAC and different dosages used (which is only mentioned at the later stages of the "results") no mention of other conditions like pH and Temperature range that affects water viscosity and sludge blanket conditions. Also a clearer table concluding all water characteristics during the experimental period May to end July is required (I did not see any supplement to the paper where all my above points could be included).

6. At "3.1 Short term monitation?" (do you mean "monitoring"?

7. The results are not divided as "results and discussion" where all the results could be explained all together, but each result is discussed separately in turn which in my view is less effective for the concluding points. A separate "discussions" chapter and then "conclusions" would be more effective.

8. There is no mention if the sludge was automatically discharge to maintain a constant sludge blanket level and concentration and how it was controlled.

9. When referring to PAC concentration it is mentioned that "PAC dosage was 4 l/min." The same is also in Fig. 7a. The correct scientific way of mentioning concentration would be as mg/l and not 4 l/min. that is correlated to the water flow and the liquid PAC density. So please correct.

10. There was mention of the pH change (decrease) as a result of PAC addition but no mention of pH correction if any to maintain constant quality and better operational conditions (at least it could have been experimented at bench scale to see if it had an advantage although pH adjustment means more costs, but sometimes the advantages balance the cost).

 

 

 

 

 

 

Author Response

Thanks to the reviewer for the constructive comments and agreeing with the highlights and introduction of this study. Please refer to the attachment for comments.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript described the monitoring of occasional rains that occur during dry seasons often stir up the bottom sediment of reservoirs, which leads to high turbidity and electrical conductivity in raw waters received by water utility companies. A newly developed real-time precision multi-layer sensor (RPMS) system was used to monitor a high-speed flocculation flat-bottomed sludge blanket clarifier (HFSBC) pond in real time to solve the water quality problems caused by drought and flood conditions.

The heavy-metal difference in soluble and solid metal contents differ d alot, could you approve that monitoring was precise regarding to metal quantities difference in water and solids?

The RPMS is capable of monitoring the thickness of the sludge blanket; if the coagulation and sedimentation processes of the HFSBC are not working well, the sludge blanket will be thin and have a low sludge concentration- more proofs needed to state that.

Conversely, if the HFSBC is working properly, the sludge blanket will have a thick and highly concentrated layer of sludge. Any heavy metals that are not removed by water treatment processes will enter the water supply network, which will result in poor water quality for end users- in your case heavy metal in soluble ophase was low so not causing hazards to water systems .

. Against the backdrop of intensifying climate change, the enhancement of automated monitoring systems and adaptation processes will be an important part of efforts to minimize and resolve acute changes in water quality.

Current work introduce important problem solving, however, figures should contain error bars estimations and more replicate experimental measurements .

Validation of results is highly recommended 

 scheme could be added to experimental setup structure.

Some literature should be mentioned regarding to control of water treatment processes:

Enhanced efficiency of nitritating-anammox sequencing batch reactor achieved at low decrease rates of oxidation–reduction potential

I Zekker, A Kivirüüt, E Rikmann, A Mandel… - Environmental …, 2019

Author Response

Thanks to the reviewer for the constructive comments and agreeing with the highlights of this study. Please refer to the attachment for comments.

Author Response File: Author Response.docx