Implementing Circular Economy in the Production of Biogas from Plant and Animal Waste: Opportunities in Greenhouse Heating
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsI am pleased to be invited for reviewing the manuscript entitled “Implementing circular economy in the production of biogas from plant and animal waste: Opportunities in greenhouse heating”. This study explores greenhouse heating using thermal energy from a biogas plant, examining the biogas plant’s electricity requirement. It also assesses greenhouse heating requirements depend on crop type, location, weather conditions, sunlight exposure, and heat loss based on covering materials. The topic of this study is quite practical and interesting, the analysis is comprehensive, and the results and discussion is meaningful and insightful. However, there are some minor problems the authors need to revise and improve according to my comments and suggestions.
Here are the details of the comments.
(1) The abstract of this manuscript is somewhat not clear, please follow the structure by “one sentence for introduction, one sentence for the data and research method, one sentence for the key findings, and one sentence for the policy implications/suggestions”. This logic will make it more concisely and will help the readers to understand the paper.
(2) The introduction section should be fulfilled by more contents and incorporate more references. And some paragraphs can be incorporated into one paragraph, such as paragraph 2 and 3.
(3) It is suggested the authors to conduct a literature review to show their research contributions of this study, at least should there have one subsection that for the literature review.
(4) The conclusion section should be revised by incorporate more practical suggestions. Besides, the authors should list the research limitation of this study and research suggestions for other researchers.
(5) There are some typing mistakes and grammar problems, please carefully check it, and editing service by MDPI can be a good choice.
Author Response
Comments 1: The abstract of this manuscript is somewhat not clear, please follow the structure by “one sentence for introduction, one sentence for the data and research method, one sentence for the key findings, and one sentence for the policy implications/suggestions”. This logic will make it more concise and will help the readers to understand the paper.
Reply 1: The abstract has been revised according to the reviewer’s suggestion, following the recommended structure to ensure clarity and conciseness.
Comments 2: The introduction section should be fulfilled by more contents and incorporate more references. Some paragraphs can be incorporated into one paragraph, such as paragraph 2 and 3.
Reply 2: Additional content and references have been added to the introduction. Paragraphs in lines 31-52, 69-86, 129-143, 145-162, 267-286, 303-318, 319-335, 352-368, and 369-389 have been merged to improve logical flow and readability.
Comments 3: It is suggested the authors conduct a literature review to show their research contributions of this study. At least one subsection should be dedicated to the literature review.
Reply 3: A comprehensive literature search was conducted, and no studies addressing this specific topic were found. A subsection dedicated to the literature review has been added to highlight the study’s unique contributions.
Comments 4: The conclusion section should be revised to incorporate more practical suggestions. Additionally, the authors should list the research limitations and provide suggestions for future research.
Reply 4: The conclusion has been revised to include practical suggestions, research limitations, and recommendations for future studies.
Comments 5: There are some typing mistakes and grammar problems. Please carefully check the manuscript. Editing services from MDPI can be a good choice.
Reply 5: A thorough proofreading of the manuscript has been completed, addressing typographical and grammatical errors.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear authors,
After evaluating the manuscript, I consider it to be in line with the themes published in Agriengineering after observing the adjustments described below:
GENERAL COMMENTS
The article has great potential for publication due to its relevance, as the theme of the application of the circular economy in the production of biogas for heating agricultural greenhouses is highly relevant, aligning with the sustainability objectives and the context of the European Green Deal. Additionally, I highlight the relevant contribution of the study and the theme addressed, robust methodology, quantifiable results with economic analysis (annual profit of €504,549 from the sale of surplus electricity), enriching the practical impact of the study, local and global relevance. Furthermore, I highlight the positive aspect of the article, which reinforces the environmental benefits of anaerobic digestion, such as the reduction of greenhouse gas emissions and the use of agricultural and livestock waste. However, to make it suitable for publication in Agriengineering, it will be necessary to improve the organization and structure of ideas in the manuscript, as well as to deepen the critical discussion. Furthermore, it is up to the authors to increase the economic detail in the manuscript. To guide the authors, I suggest adjustments to the following aspects in the manuscript.
ASPECTS TO BE ADJUSTED
Clarity in structure: Some sections (e.g.: Introduction) are extensive and could be more concise, with greater focus on key points and references directly related to the topic.
Detailing of regional data: The analysis is focused on Thessaly, but the study could briefly explore the adaptations needed for other regions or climates, increasing practical applicability;
Reference review: although many sources are cited, some references are dated (prior to 2020) or focus on regional studies. I suggest citing more recent and global studies to strengthen the theoretical basis.
More critical discussion: Despite presenting solid results, the paper lacks a more critical discussion of implementation challenges (e.g., installation costs, regulatory barriers, and farmer acceptance);
More detailed economic aspects: Profit from electricity sales is mentioned, but operational costs, biodigester maintenance, and possible government subsidies could be discussed to provide a more complete economic analysis.
Exploring alternative uses of biogas: Despite the focus on greenhouse heating, the paper could briefly explore other potential applications of biogas, such as vehicle fuels or fertilizers, to maximize the impact of the study.
Minor corrections: The paper presents good technical writing, but additional proofreading to avoid redundancies and correct possible typographical errors would be beneficial. Some graphs and tables (e.g., Table 1) could be clearer, with better formatting for quick reading.
Author Response
Comments 1: Some sections (e.g., Introduction) are extensive and could be more concise, with greater focus on key points and references directly related to the topic.
Reply 1: While another reviewer suggested adding more content, we believe the current structure balances conciseness and comprehensiveness. Key points and references have been refined for clarity.
Comments 2: The analysis is focused on Thessaly, but the study could briefly explore the adaptations needed for other regions or climates, increasing practical applicability.
Reply 2: The model was tested in two distinct regions of Greece (Florina and Trikala) with significantly different climatic conditions. Therefore, the model is adaptable to various climatic zones worldwide, especially rural areas.
Comments 3: Although many sources are cited, some references are dated (prior to 2020) or focus on regional studies. I suggest citing more recent and global studies to strengthen the theoretical basis.
Reply 3: Four recent global studies have been added to strengthen the theoretical foundation and update older references.
Comments 4: The paper lacks a critical discussion of implementation challenges (e.g., installation costs, regulatory barriers, and farmer acceptance).
Reply 4: A discussion of implementation challenges, including installation costs, regulatory barriers, and farmer acceptance, has been added.
Comments 5: Profit from electricity sales is mentioned, but operational costs, biodigester maintenance, and possible government subsidies should be discussed to provide a more complete economic analysis.
Reply 5: Economic metrics, including operational costs, biodigester maintenance, and potential government subsidies, have been incorporated based on data for a 500 KW biodigester.
Comments 6: Despite the focus on greenhouse heating, the paper could briefly explore other potential applications of biogas, such as vehicle fuels or fertilizers, to maximize the impact of the study.
Reply 6: Alternative uses of biogas, including its application as vehicle fuel and in fertilizer production, have been briefly discussed.
Comments 7: The paper presents good technical writing, but additional proofreading to avoid redundancies and correct typographical errors would be beneficial. Some graphs and tables (e.g., Table 1) could be clearer, with better formatting for quick reading.
Reply 7: Proofreading has been completed to address redundancies and typographical errors. Table 1 and other figures have been reformatted for improved clarity and readability.
Author Response File: Author Response.pdf
