Enhancing the Fermentation Process in Biogas Production from Animal and Plant Waste Substrates in the Southeastern Region of Bulgaria
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsComments on the manuscript: Enhancing the technological process for producing biogas from animal and plant waste substrates in the southeastern region of Bulgaria
The title is not in line with the objective.
The objective of the work is unclear, the abstract says one thing, the introduction says another. Need to make it clearer.
What is the main limitation nowadays for producing biogas from animal and plant waste substrates? Discuss
When not intended for bioenergy, what are these animal and plant residues used for? Discuss
Would this described process have the same efficiency in tropical countries? Discuss
Comments on the Quality of English LanguageNothing that compromises the quality of the manuscript
Author Response
Comment 1: The title is not in line with the objective.
Dear Reviewer, thank you very much for the constructive comments on our paper! Yes, on second glance, we agree about the paper's title, so we suggest the following change to it: “Enhancing the fermentation process in biogas production from animal and plant waste substrates in the southeastern region of Bulgaria”. This way, the topic of the paper will be clearer and in line with the objectives and the content of the study.
Comment 2: The objective of the work is unclear, the abstract says one thing, the introduction says another. Need to make it clearer.
Yes, thank you once again for this comment! We agree with the initial misleading in the connection between the abstract and the introduction part. We introduced small changes in the abstract and we significantly revised the introduction, outlining the study objectives.
Comment 3: What is the main limitation nowadays for producing biogas from animal and plant waste substrates? Discuss
Biogas obtained through the fermentation of plants and animal biomass is mainly used for firing a cogeneration plant for the simultaneous production of electricity and thermal energy. Given that these installations are outside populated areas, it is very difficult to fully utilize the produced thermal energy. This excessive thermal energy could be used for district heating as well as heating greenhouses. The partial use of thermal energy is also one of the reasons for the lower final efficiency of the facility. From a regulatory point of view, the limitations come mainly from the type of technology used and the release of harmful substances into the atmosphere during fermentation. A reduction in the relative number of cattle, respectively the amount of animal substrate, is another limitation. This comment took place in the revised version of the paper as well.
Comment 4: When not intended for bioenergy, what are these animal and plant residues used for? Discuss
If silage and manure loads are not used for bioenergy, they have several other applications. For example, silage mass with little processing can be used for feeding farm animals and the manure mass can be used to fertilize the soil. In the second case, it is necessary to keep the manure mass in open-type storages for a certain period, for the maximum release of ammonia before fertilization. When the manure and silage mixture is processed in the digestor, for the purpose of bioenergy production, the output substrate has the properties of a very good soil fertilizer, including a product with a reduced ammonia content. This comment took place in the revised version of the paper as well.
Comment 5: Would this described process have the same efficiency in tropical countries? Discuss
In the presented research, the efficiency of the fermentation process depends on maintaining of a certain temperature in the digester, which provides not only a suitable environment for the growth of the microbiological culture but also covering the heat losses. Of course, in the presence of a tropical climate, where the average monthly temperature for all months of the year varies from 21oC to 30oC, the amount of heat energy would be significantly less than the case considered, which will result in a higher efficiency of the installation.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I find your research on biogas production intriguing and potentially insightful. However, for a more comprehensive and publishable paper, I suggest several adjustments:
(1) There is something wrong in using multiple citations. For instance, (second page):
Precise analyses, based on the specific properties of the raw materials are conducted, to determine the most suitable approach and enhance the 68 process efficiency [23], [24], [25].
This should actually contain the citation like this: [23, 24, 25]. Please correct where it is the case, there are various like these.
(2) Use the metric measurement system; the dot as decimal symbol and comma to separate digits into groups of three (ex: 0.25 123,235.76 231,435). Currently you are using both comma and dot for decimals. For instance:
After the analysis of the energy consumption of the biogas plant for one year, it was found that the annual thermal energy for the fermenter is 819.94 MWh/year. The annual consumption of electricity for own needs is 820 kWh/day, or 299.63 MWh/year. The net annual production of electricity and heat is 6099 MWh/year and 5656 MWh/year, respectively.
Within table you are using commas: 33,00% 31,35%
(3) Please, add sources for all tables and figures.
(4) There is a lack of consistency in writing references. The journal’s rules should be followed.
(5) The authors should try to mention the difficulties of developing such a research, or the limits of the study in the final section of the article.
Comments for author File: 
Comments.pdf
The overall level of English is good.
Author Response
Comment 1: There is something wrong in using multiple citations. For instance, (second page):
Precise analyses, based on the specific properties of the raw materials are conducted, to determine the most suitable approach and enhance the 68 process efficiency [23], [24], [25].
This should actually contain the citation like this: [23, 24, 25]. Please correct where it is the case, there are various like these.
Dear Reviewer, thank you very much for the constructive comments on our paper! Yes, we entirely agree with this remark, and we have introduced the changes in the paper. Thank you once again!
Comment 2: Use the metric measurement system; the dot as decimal symbol and comma to separate digits into groups of three (ex: 0.25 123,235.76 231,435). Currently you are using both comma and dot for decimals. For instance:
After the analysis of the energy consumption of the biogas plant for one year, it was found that the annual thermal energy for the fermenter is 819.94 MWh/year. The annual consumption of electricity for own needs is 820 kWh/day, or 299.63 MWh/year. The net annual production of electricity and heat is 6099 MWh/year and 5656 MWh/year, respectively.
Within table you are using commas: 33,00% 31,35%
Thank you for this comment, again! The necessary changes are introduced into the manuscript.
Comment 3: Please, add sources for all tables and figures.
Thank you for this clarification! All figures and tables in the presented manuscript are developed by the authors.
Comment 4: There is a lack of consistency in writing references. The journal’s rules should be followed.
Yes, thank you for this! The references have been revised in the updated version of the manuscript.
Comment 5: The authors should try to mention the difficulties of developing such a research, or the limits of the study in the final section of the article.
The main difficulties in the present study were related to the maintaining of certain regime parameters in the digester, which would ensure proper growth of the microbiological culture, respectively optimal biogas production. All this takes place with variable outdoor air temperature. It should be noted here that the process is extremely dynamic, i.e. fresh mass is continuously supplied to the digester, as well as a certain mass is taken out, which is the reason for a constant change of the mode parameters of the fermenter. This comment took place in the revised version of the paper as well.
