E-Learning Proposal for 3D Modeling and Numerical Simulation with FreeFem++ for the Study of the Discontinuous Dynamics of Biological and Anaerobic Digesters

Round 1

Reviewer 1 Report (Previous Reviewer 2)

This article is an e-learning proposal with a 3D code in FreeFem++ to recreate the behavior of anaerobic microorganisms in unstirred anaerobic reactors with intermittent feeding. This is for me the main interest of this article.

It can be published with minor corrections:

As the code is in the appendix of the document, it seems to me pointless to include it in lines 168, 175 and 179.

L168 Freefem+ instead Freefen+

L258 equations and not ecuations

Author Response

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Reviewer 2 Report (New Reviewer)

This paper is about E-Learning using FreeFem++ to study discontinuous dynamics of biological and anaerobic digesters.

It explains the results that are expected to be highly useful as educational materials.

However, some formal aspects need to be modified for publication.

1. It is appropriate for the captions of figures to be written in a modified form rather than a descriptive form.

2. The first letter of some sentences or phrases is not capitalized. (e.g., Figure 5 caption)

3. In the case of Figure 7, "a, b, c, e" needs to be modified alphabetically, and all displayed images need explanations.

4. Lines 231 to 243 contain overlapping content. Please correct accordingly. Also, line 243 must end with a period (.).

* Please be sure to revise the basic sentence format as a whole.

Author Response

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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

The authors have made considerable effort to improve their work. Many changes and additions have been done to better clarify the goals and the results in the paper, unfortunately unsuccessful. The main reason is loss of originality and novelty, just standard numerical schemes are implemented in a software environment. A second reason is the extremely bad English. There are many grammar mistakes, typos, strange punctuation, too large sentences (e. g. lines 81-86), the latter being difficult to read and to understand. Any authors’ attempt to describe or to explain some results fails due to the bad English, too.

Author Response

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Reviewer 2 Report

The authors claims that with their model, it’s possible to improve the students’ understanding and assess the student’s  knowledge about the internal functioning of anaerobic processes within a fed-batch unstirred tank reactor. In my point of view, it would be more interesting for students to use a more realistic model for anaerobic digestion than that too simplistic and far from reality proposed in this paper and show that  that mixing enhances the performance of anaerobic digestion (AD), creating a homogeneous distribution of soluble substrates, biomass, pH, and temperature. See for this purpose the recent article: Yohannis Mitiku Tobo, Usman Rehman, Jan Bartacek, Ingmar Nopens; Partial integration of ADM1 into CFD: understanding the impact of diffusion on anaerobic digestion mixing. Water Sci Technol 15 April 2020; 81 (8): 1658–1667. doi: https://doi.org/10.2166/wst.2020.076

In the "state of the art" part, it would be useful to specify that CFD modeling for AD processes is not yet very developed.

Nevertheless, this article can be published if the authors take into account the previous remark.

Author Response

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Reviewer 3 Report

1.    This paper is difficult to evaluate the originality of the content.

2.    This paper showed the tool for education mainly for students.

The visual demonstration is indeed important in education area.

What kinds of tool are applied and how to establish mathematical models

are essential. There are many choices for this. It is skeptical that the concept of

this paper is the best.

3.    The list of nomenclatures is needed. Some terms are not defined.

4.    It should be described how the authors selected parameters. Modelling is

dependent on the selection of parameters.

5.    The concept of this paper is very simple. 2D modelling may be effective in small reactors. Actually reactors are 3D and large and diffusion mechanism is more complicated. 

6.    The figures are not easily understood.

7.    References format is inconsistent

Author Response

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