Improved Cyanobacteria Removal from Harmful Algae Blooms by Two-Cycle, Low-Frequency, Low-Density, and Short-Duration Ultrasonic Radiation
Round 1
Reviewer 1 Report
Well done. The MS can be accepted in the present form.
Reviewer 2 Report
This is a very well written and presented paper, and contains useful information. However, the study design is limited, as mentioned by the authors at the end of the paper. The water quality parameters are highly controlled. It would be good to discuss and study how the results would come out when the water contains colloidal and suspended solids, dissolved solids, other aquatic habitat species such as plants, fish, zooplankton, etc. It is also important to investigate the adverse impacts on the aquatic habitat. Another consideration would be the effective radius, as mentioned in the paper, the attenuation could be significant and the coverage area could be very limited in a real water body setting.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Review water-758816
March 27, 2020
General comments:
This manuscript presents several important findings in a readable manner. The proposed mechanism is to collapse gas vacuoles (or vesicles) using pulses of ultrasound. The experimental procedure verifies that and shows some steps towards optimizing energy spent accomplishing this disruption. The conclusions, however, assume that this method will be just as successful in a natural water body without recognizing the scale-up issues. For example, all the work for this manuscript was done in small plastic containers. It would have been very interesting to test their optimum protocol in a larger container.
Specific recommendations:
I have things that need to be corrected:
- Need to fix Figure 3. I think the wrong graphic was inserted.
- Need to remove any claims about toxins unless these were measured. Leaving toxins in the water is a major problem with any HAB treatment
I have a suggestion that I think would improve the paper. The manuscript could be streamlined by leaving out recipe for BG-11 and the equation for ultrasound absorption unless the authors are making some specific point about the details.
Line-by-line:
26- I don’t know what you mean by “industrial equipment”.
33- “very disrupting water-related contaminants” is redundant to the phrase harmful algal blooms.
35- Leave off the first part of the sentence and just start with Microcystis and their neurotoxic ..
63 – This is a very important claim and essence of your paper. I’d put it right up near the top instead of 60 lines into the paper.
63 – It’s my understanding that the vacuoles hold the protein vescicles and it’s really the vescicles that collapse under ultrasound.
71 – Single cycle and two-cycle are confusing. Might I suggest, single pulse and double pulse?
85 – No need to mention BG-11 details unless you modified them significantly. Readers will skip right over this.
101 – Claiming that only one variable was changed isn’t clear enough. Describe how frequency was explored, time of pulse was explored, etc.
119 – Again, how to use a cell counting chamber is rudimentary. No need to describe in this paper.
126 – You compare to the control, but why didn’t you use comparison, before and after treatment? Just need to explain.
154 – need to explain that the energy was held constant across these frequencies
161 – wrong graphic, embarrassing but we’ve all done it
181 - unless you're going to discuss these other factors (viscocity, density, etc), then this equation is not needed. You could simplify the equation just to deal with frequency. That would make your point more obvious. However, this equation could also be used to predict whether increased temperature would help or hinder this method, since rho, nu are functions of temperature
188- I don't think this follows logically - longer distances could effect more organisms
197 – Figure 4. RR is based on cell counts, so why is RR so much higher impact than decreased chlorophyll?
207 – You didn’t measure microcystin, can’t claim anything
235 – This is a very useful finding – should be mentioned in the abstract.
248- everything you are measuring is in terms of volume or distance, not area
261- why don't the second pulses show up as decreases on the graphs?
279- might be good to reliable this parameter something like "energy effectiveness factor". Many readers will think 100% would be the best efficiency and it might confuse them at first. You'd have to change the term up in the line 142 also.
Reviewer 2 Report
This manuscript Improved Cyanobacteria Removal from Harmful Algae Blooms by Two-cycle, Low-frequency, Low-density, and Short-duration Ultrasonic Radiation of Haocai Huang, Gang Wu, Chaowu Sheng, Jiannan Wu, Danhua Li, Hangzhou Wang seems interesting and addresses an important issue. The authors provide a lab-based experiment for the utilisation of ultrasonic radiation to eliminate harmful algal blooms in aquatic ecosystems.
This is a well written and interesting paper. I recommend that the paper is accepted for publication following some minor clarifications.
Page 4. Line 137: Mention more clearly that you cite studies of other working groups here. Or emphasize if this statement is of previous studies of your working group.
Page 5. Figure 3: Is identical to Figure 4. Change Figure 3 into the right chart with different ultrasonic frequencies instead of different durations as given in Figure 4.
Page 10. Line 302: add in situ after “… the application of the experimental device …”
As a suggestion:
Give a more detailed statement about the need of a suitable large-scale device for field studies. How many devices would you need for the restoration of lake like Dianchi Lake, Kunming with surface area 298 km2 (115 sq mi)?
Discuss in a scientific context possible risks for other organisms in the aquatic ecosystem, e.g. zooplankton, fish fauna, are there any negative impacts on the swim bladder?
References
Please write species names in italics
Lines 320, 327, 346, 347, 348-349, 357, 364, 365
Page 11. Line 346: delete the space after “aeruginosa”
Reviewer 3 Report
1. Harmful algae blooms are an issue longer than just recent years as stated in Introduction. 2. Microcystins are not primary neurotoxic; the evidence for their neurotoxicity is not strong. Instead, they are well known hepatotoxic agents, with mechanisms of action established over the last two or so decades 3. According to methodology, the cultures were not axenic, antibiotic was not used in culture medium - this should be stated. 4. Is your bg-11 different anyhow to typical bg-11 medium for Microcystis? If so, please just state the difference in the text, there is no need to provide a separate table with medium ingredients. 5. Although authors mention that many methods of cyanobacterial removal can lead to an increase of cyanotoxins (such as microcystins) in the water column, they provide no direct evidence in their study that their treatment removed microcystins. This provides a significant limitation; authors only refer to other studies in which ultrasonic irradiation at 640 kHZ caused a rapid degradation of MC-LR - this is not enough. Microcystis can produce other microcystins analogues than MC-LR as well as other toxins such as cyanopeptolins and others. Without providing a rigorous analytical investigation of the medium before and after a treatment one cannot conclude whether this method is of any use to decrease human health threat. 6. How can you apply such a method in situ, on a large scale? This method appears purely experimental.