Ozone as a Catalyst of Surplus Activated Sludge Hydrolysis for the Biogas Production Enhancement

Round 1

Reviewer 1 Report

Paździor et al. have written an interesting paper focused on ozone as a catalyst for the biogas production enhancement, obtaining results in term of amount of produced biogas and methane content. In my humble opinion the topic studied, the set of methods used and the results are clear and concise. However, I report some of my minor considerations by scrolling the text. Thanks for your attention and if you want to consider them.

INTRODUCTION

38) If cited paper n. 3 encompasses the three categories of methods for sludge disintegration, I would move [3] close to disintegration at 35).

58) 300 mL on how much substrate? I would add a more specific yield.

68) I would also add the C/N as an important parameter.

Citing from the literature (if available) or expressing a personal consideration, I would also write a few lines (here or in the conclusions paragrapgh as future development for example) about the Life Cycle Assessment of the possible scale-up of this process. I mean: by carrying out this treatment with ozone, which still requires external inputs, would anaerobic digestion always remain the sustainable process it aims to be? If you agree with this my perspective, of course.

RESULTS & DISCUSSION

111) Although the no significant influence, why did you prefer ISR = 1 between the two values?

157) Figures 4a and 4b misalignment to the text.

193) Shouldn't “The influence of ozonation on BMP” be 2.4 as paragraph?

204) Table 3: Although not the purpose of your paper, how do you justify such a difference between BMP theory and bottles practice?

206) Shouldn't “The influence of ozonation on methane fermentation kinetics” be 2.5 as paragraph and written in italics?

MATERIALS AND METHODS

I would move the Materials and Methods paragraph between "Introduction" and "Results and Discussion".

260) Typing error (oC) in °C.

250) So the volumes of biogas produced that you report are already net of the contribution of the inoculum?

252) Why didn't you at least calculate the pH also during the tests and not just at the beginning and at the end? It would have been useful because correction of pH could be required to increase the biogas yield if the value was not within the optimal range.

Author Response

Thank you very much for the valuable remarks concerning our manuscript. According to your advices the article was corrected. Please find enclosed detailed response to all your comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript was wrongly converted to pdf, because at the end you give 3. Conclusions, and later 4. Materials and Methods. Please make manuscript normally readable.

But in general manuscript could be reviewed after layout modification.

See attached document for detailed comments.

Comments for author File: Comments.pdf

Author Response

Thank you very much for your valuable comments. Please see the attachment containing detailed repsonse to your comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The structure of the manuscript is still messed up. Introduction -> conclusions -> results -> methodology. Please number parts in normal order.