Mathematical Model of a Thermophilic Anaerobic Digestion for Methane Production of Wheat Straw
, Venelin Hubenov 1, Ivan Simeonov 1 and Olympia Roeva 2Round 1
Reviewer 1 Report
. Model validation could be more explained to clear undersand.
Some references are not new, better to change.
Author Response
Dear reviewr,
We would like to thank you for the valuable comments and suggestions so far.
The last changes to the paper are presented in red color in order to be easily visible to the editors and the reviewers.
Parts of the text have been revised in order to avoid similarity found in iThenticate report.
Model validation could be more explained to clear understand.
The following sentence was added in the Section 3.2.3. Model validation: The proposed models based on GA and SQP2 algorithms, with the parameters listed in Table 4, are simulated with the new initial substrate organic load (35 ml/dm3 instead of 30 ml/dm3), as well as with the new initial values of cellulose, glucose, acetate and methane in the new experimental data set. The obtained results (from the comparison between the model and the new dataset) are shown in Fig. 3 (cellulose and glucose dynamics) and Fig. 4 (acetate and methane dynamics).
Some references are not new, better to change
Some recent references are added, as well as some of the older references have been replaced with newly published ones (all highlighted in red color).
Best regards,
Elena Chorukova
Reviewer 2 Report
Dear Authors,
It was my pleasure to do a review of your article.
I believe that it deserves to be published, it is written in a clear and reliable manner. The combination of practical research with a simultaneous attempt at theoretical representation of the occurring processes deserves praise. However, after reviewing the paper, a few minor comments come to mind, which need to be taken into account in order to better perceive the content.
(1) In line 62 there is red font in the word modelling in the letter "l".
(2) How was the methane content in g/dm3 calculated? Was a conversion based on the normal cubic metre used when converting gaseous methane to a unit of mass?
(3) Why do the methane fermentation results (Table 1, 2) show only 15 days? Did the study last only that many days?
(4) A description of the obtained results of methane fermentation, the course of the experiment in chapter Results and discussion, Experimental studies would be useful.
(5) For the models obtained and validation performed it would be reasonable to present the errors (Mean Absolute Error-MAE, Mean Absolute Percentage Error-MAPE), even if only for the selected, most favourable model.
Best regards
Author Response
Dear reviewer,
We would like to thank you for the valuable comments and suggestions so far.
The last changes to the paper are presented in red colour in order to be easily visible to the editors and the reviewers.
Parts of the text have been revised in order to avoid similarity found in iThenticate report.
(1) In line 62 there is red font in the word modelling in the letter "l".
Corrected.
(2) How was the methane content in g/dm3 calculated? Was a conversion based on the normal cubic metre used when converting gaseous methane to a unit of mass?
Thank you for the comment. We made a technical mistake. The dimension g/dm3 has been corrected to ml/dm3 throughout the text. The biogas volume was measured by the water displacement method, using a graduated cylinder and the methane content was measured in % (volume). The final methane concentration was calculated by multiplication by the % concentration.
(3) Why do the methane fermentation results (Table 1, 2) show only 15 days? Did the study last only that many days?
Yes, the process duration was 15 days. After that period our investigations showed negligible, near to zero, values of biogas production.
(4) A description of the obtained results of methane fermentation, the course of the experiment in chapter Results and discussion, Experimental studies would be useful.
The following explanation about the experimental studies was added: The mechanically chopped wheat straw with the corresponding quantity (30 ml/dm3 or 35 ml/dm3) is suspended in distilled water and inoculum from a working biomethane generaating bioreactor 30% (vol) is also introduced in the batch process which continues 15 days. The inoculum quantity is previously determined as it ensures good buffer capacity at the beginning of the process. Stirring is maintained at 100 min-1.
(5) For the models obtained and validation performed it would be reasonable to present the errors (Mean Absolute Error-MAE, Mean Absolute Percentage Error-MAPE), even if only for the selected, most favourable model.
The value of Mean Absolute Error is calculated and presented in Table 4. The mean absolute percentage error (MAPE) works best if there are no extremes to the data and no zeros. In our case the initial value of methane is 0, so we cannot calculate MAPE.
