Removal of Clostridium perfringens and Staphylococcus spp. in Microalgal–Bacterial Systems: Influence of Microalgal Inoculum and CO2/O2 Addition
, Sarah Lacerda Farias 1, Bruno A. B. dos Reis 1, Mayara Leite Serejo 4, Gustavo Henrique Ribeiro da Silva 3 and Marc Árpád Boncz 1Round 1
Reviewer 1 Report
The topic of the paper is interesting and suitable for the journal. The authors study the influence of the inoculum and the addition of O2 and CO2, on the pathogen-removal capacity of microalgae-bacterial systems. Specifically, this study assess the influence of two microalgal strains (Chlorella vulgaris and Scenedesmus acutus Meyen) as well as the addition of CO2 and O2 on the removal of two microorganisms disinfection indicators (C. perfringens and Staphylococcus spp.) present in domestic wastewater.
After reading the paper, moderate revision is required to address the following issues prior to possible publication:
(1) Section 2.2, lines 108 – 110. Is there no variability in the measured parameters of the wastewater? How many samples were taken? Were they grab or integrated samples?
(2) Section 2.3 Experimental set-up.
· It is not clear how many times the lab-scale batch reactor was fed during each experiment. Please clarify.
· It is not clear what was the hydraulic retention time (HRT), and the solids retention time (SRT). Please indicate. Note that SRT is a very important factor for the bacterial consortium.
· Which criteria was used for the amount of gases suplied?
(3) Figure 2 (page 6):
· This is the first figure in the document, not the second. Change it in the title as well as in the text.
· Include the units of the y-axis in the plots.
(4) Line 273 (page 7) Include the units of the value 0.01.
(5) Motivate why the inactivation rate obtained in this study is so different from that obtained by Al-tameemi and Kadhim (2019). What could be the causes of this huge difference?
(6) Page 8. The figure is named Figure 1, but it is the second figure.
· Change the number in the title and in the text.
· Check the name “Cholorrella” in the figure. Correct it.
(7) Line 291. Nitrifying bacteria do NOT remove COD. Please remove these bacteria from the sentence.
(8) Despite that along each experiment there is a time-evolution of the concentrations, there is no figure showing the temporal evolution of any relevant variable. Please include at least one or several experiments the time-series evolution that allows the determination of the inactivation rate, and other relevant measured variables (like COD).
(9) How in your microalgae-bacterial systems can distinguish between the pathogen removal due to bacteria and the pathogen removal due to microalgae, or if there were synergic effects?
(10) The effect of CO2 addition on water depends on the alkalinity of the water and it obviously also affects the economics of the dosing. Discuss if the results could be expected to be different depending on the alkalinity of the water.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript is interesting, original and well written. Actually, I only have one suggestion is to add the results of a control that does not contain the addition of algae. Curiously, the manuscript does not include this type of control.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Ruas et al. analyzed the effects of microalgal strains and the addition of CO2 and O2 on the removal of C. perfringens and Staphylococcus spp. from domestic wastewater in microalgae-bacterial systems. The Language need improvement to be more accurate and standardized.
Specific comments:
Abstract:
-L14-21: The first three sentences should be more concise. Background description is too much for abstract. Why to add CO2 and O2? What are the main methods?
-L19: The full name should be added of E. coli when firstly occurred.
-L20-22: Clostridium, Staphylococcus etc. should be italic; the number 2 of CO2 and O2 should be subscript.
-L26-28: Beyond the support of this study. Were there any toxins or photooxidation products that had been tested in the experiment?
Introduction:
-L43-51: Beyond the topic.
-L52-57: HRAPs, WWTP, should be fully given when firstly occurred.
-L91-94: Too general. Is this an experimental study or a review? What are the key objectives, or any hypotheses?
Material and Methods:
-L97: Scenedesmus and Chlorella should be shorted for S. and C. after the first occurrence. The same below.
-L99-101: Any identification of such strains before inoculum?
-L141: How long did this experiment last?
Results and discussion: It's better to separate this section into two parts. Discussion could be set as a separate section.
-Figure 2: What are the abbreviations of C1, 2, 3 and S1, 2, 3 short for? Should be described in figure captions.
-Table 4: The statistical differences should be indicated between the treatments.
Conclusions:
-L329: “indicate” means the conclusion is from speculation.
-L331-333: Beyond the support of this study. No toxins or photooxidation had been tested here.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Materials and Methods
Line no-95: Authors are requested to add a diagram of the laboratory setting of the experiment.
Result/Discussion
Line no-255: Could you please add the test result and p-value by the statistical test?
References:
Line no- 393: Please check references 4, 57, and 58 for adequate information.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have correctly addressed the comments.
I consider that the paper can now be accepted for publication.
Reviewer 3 Report
I'm pleased to notice that all the comments have been responded reasonably. Thanks. I still recomend to separate the results and discussion.
