Microalgae Cultivation on Nutrient Rich Digestate: The Importance of Strain and Digestate Tailoring under PH Control

Round 1

Reviewer 1 Report

I have read this research manuscript “Microalgae cultivation on nutrient rich digestate: the importance of strain and digestate tailoring under pH control”. The study shows some promising results. This manuscript is generally well organized and well written, some minor comments are:

1. Some of the figures are not clear enough, and are difficult to figure out, please improve the resolution of the figures
2. Please identify and highlights the difference between the aim of your study and other previous studies
3. Add more results and findings of the study in the abstract, the abstract should be more results and objective oriented.
4. Please include more information about how did you take your samples every day, and Whether sampling affects the stability of the reactor?
5. For the determination of total proteins and carbohydrates, please include citations or references to the original method before being modified

Author Response

The authors thank reviewer 1 for taking the time to review this manuscript and they appreciate their comment regarding the quality of the presented work. The authors understand that minor comments need to be addressed to improve the manuscript and have modified the text accordingly.

A detailed response to reviewer 1 can be found in the provided attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The entire manuscript should be edited properly to remove scientific/grammatical errors......

Author Response

The authors thank reviewer 2 for their input. The whole of the manuscript has been reviewed by two English native speakers. The authors believe that a thorough review of the English and grammar of the manuscript has been carried out and that errors have been removed.

All changes can be found in the tracked changes version of the manuscript.

Reviewer 3 Report

The Manuscript “Microalgae cultivation on nutrient rich digestate: the importance of strain and digestate tailoring under pH control” requires revision before accepted for publication. The specific comments are given below.

1. In the abstract, provide the most important numerical results of your research.
2. The basic characteristics of Chlorella vulgaris and Scenedesmus obliquus microalgae should be provided in the materials subsection.
3. More basic information (e.g., concentration, brand, etc.) about chemicals (e.g., NH₄Cl, etc.) should be provided in the materials subsection.
4. What were the colors of the digestates?
5. What was the digestate diluted with?
6. Laboratory tests require repeatability. Add standard deviations to the results in tables, figures, and text. Write down the number of times the repetitions were performed.
7. All the figures are of poor quality, not very visible. Correct it.
8. Extend your conclusions with the most important results (numerical values).
9. Refresh your literature. Include the latest research related to the cultivation of microalgae on digestate:

https://doi.org/10.3390/en15082912

https://doi.org/10.1016/j.biteb.2019.03.007

https://doi.org/10.1016/j.algal.2020.101841

https://doi.org/10.3390/app11031056

Author Response

The authors thank reviewer 3 for taking the time to review this manuscript and they appreciate their comment to improve the presented work. The authors have addressed the specific comments given by reviewer 3 and believe that the manuscript is now improved.  

A detailed response to reviewer 3 comments can be found in the provided attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Thanks for the corrections. Some changes and refinements are still required to improve the quality of the manuscript.

1. "Digestates were all a darkbrown color" - the color of digestates should be specified specifically, eg the color was measured directly as Pt-Co units according to ASTM D 1209.
2. Add standard deviations to abstract results and conclusions.
3. Quote the publications suggested that make a significant contribution to the study of cultivation of microalgae on digestate.

Author Response

1. "Digestates were all a darkbrown color" - the color of digestates should be specified specifically, eg the color was measured directly as

 Pt-Co units according to ASTM D 1209.

FF: The authors have added a reference previously where the turbidity of the digestate is specified, which is a reflection of the colorimetric absorbance. The authors do not have the equipment or expertise to carry out the suggested methodology but will investigate this option for future research. Additionally, membrane filtration followed by dilution removed the colour of the used digestate and consequently the authors believe that this factor was not relevant to microalgal growth performances in this specific experiment. 

2. 
   Add standard deviations to abstract results and conclusions.

FF: The standard deviations were added to the abstract and conclusion results.

3. 
   Quote the publications suggested that make a significant contribution to the study of cultivation of microalgae on digestate.

FF: Suggested publications have been added to the manuscript and are referred to under the following references numbers : 69,70