Investigating the Anaerobic Digestion of Water Hyacinth (Eichhornia crassipes) Sourced from Hartbeespoort Dam in South Africa

Round 1

Reviewer 1 Report

The manuscript implemented the batch experiments on anaerobic digestion of water hyacinth (with or without cow manure), and studied the effects of pretreatments and kinetic modelling, which had practical meanings to some extent. The novelty and organization of the paper need be improved, and the comments are as follows:

1. In the introduction, the research progress should be strengthened to present the novelty of this study, since the small batch experiments adopted in this study was not new method.

2. In the experiment set up, more information about the experiment design need be added, since some details of ratios (volume or weight?), pretreatments, sampling, etc., were not presented.

3. In the results, the significant differences among co-digestion treatments were not observed, and need be discussed. The description in Figure 3 were not correct (R1 is 1:1…)?

4. In the results, the microbial dynamics need be compared with more studies, to explored the innovational findings of this study.

5. In the results, the digestate potential as biofertilizer would not only focus on NPK, but also the other index of biofertilizer, such as organic matter, etc.

6. Some spelling and grammar errors should be revised, the sequences of titles and some text in the figures and tables need be checked. The organization of the whole manuscript must be improved, and the discussion on the results must be deepened.

The English language throughout the whole manuscript should be checked and revised following the above comments.

Author Response

Please See Attachment

Author Response File: Author Response.docx

Reviewer 2 Report

This paper, entitled Investigating anaerobic digestion of water hyacinth (Eichhornia crassipes) sourced from Hartbeesport dam in South Africa, is a scholarly work and can increase knowledge on this domain. The authors provide an interesting and original study, the content is relevant to Fermentation.

I have some general and specific comments:

- The abstract and keywords are meaningful.

- The manuscript is quite well written and welle related to existing literature.

- Why there's some words or symbols highlighted in yellow?

- How many samples of water hyacinth were harvested? Is there any seasonality and variability about samples? What is the potential amount of water hyacinth and by this way the potential recovery of energy?

- Figure 1 could be removed due to the fact that it's not so informative for the content.

- Please provide some additional information for inoculum and samples (total VFA, total alcalinity, pH, COD, Nitrogen content, ...).

- About BMP tests, please consider Holliger et al., 2016 Water Science and Technology, and Hafner et al., 2020 Water for BMP modalities and procedures.

- What is the S/X ratio or I/S ratio?

- Please check numeration about titles and subtitles (for example 2.2 ; 1.1 and 2..1) page 3 and 4

- Please provide standard deviation or accuracy of data in Table 1.

- Please express the results in normomilliters of methane per gram of VS in Figure 3 and in the text. This is the unit widely used when working in anaerobic digestion. Same comment for Figure 4.

- Is the blank (endogenous production of inoculum substracted of the curves in Figure 3?

- About subsection 3.5 digestate, please provide some data or details concerning nitrogen, phosphorus, potassium content. Such amounts of N, P, K were determined after BMP tests, it could different in real conditions of Biogas plant and for digestate production.

As it, this paper is not fully acceptable for publication and requires major revision before publication. Some additional points, data and details should be added, some points are lacking and must be improved. I recommend the following decision : RECONSIDER AFTER MAJOR REVISION.

Author Response

Please See Attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors provide a revised version of their manuscript taking in to account all the comments and requests of amendments made in the previous review. The authors provide also detailed answers to all the comments and requests of amendments. I agree with all the answers. I recommend the following decision: ACCEPT IN PRESENT FORM.