Operation of a Pilot-Scale Biogas Plant Made of Textile Materials and Application of Its Results to a Full-Sized Demonstration Plant

Round 1

Reviewer 1 Report

The authors report the operation of a textile material biodigester For biogas production in small farms. While the study provides new findings and report methodology for farmers to build their own textiles based digester  there at some issues with the manuscript.

The introduction is not in-depth, there is no literature review and knowledge gaps.

The authors should discuss studies that used a textile based reactor, advantages and limitations.

The authors should also outline the characteristics of the manure used for biogas production.

The abstract is too generic, include information about study motivation.

Although a stirrer is not used and the reason is described it is still not clear how effective mixing is attained.

Figure 1 is not clear. The digester should be the study focus 

How is the substrate fed into the system while keeping it air tight 

The authors should present results of biogas compositions is possible. 

Conclusion should be revised to include study limitations and future prospects. 

No

Author Response

Comments Reviewer 1:

1._ The authors report the operation of a textile material biodigester for biogas production in small farms. While the study provides new findings and report methodology for farmers to build their own textiles-based digester there at some issues with the manuscript.

Ok, noted. That’s right, the goal of the project was the development of a biogas plant consisting of textile materials for small farms. At the same time, this small biogas plants are qualified to be built by the farmers on site.

2._ The introduction is not in-depth, there is no literature review and knowledge gaps. The authors should discuss studies that used a textile-based reactor, advantages and limitations.

Please note the paragraph from line 87 to line 98. The actual study focuses on the experiences made at the Landshut University with the pilot scale biogas plant and the coming full-sized demonstration plant. A study on digesters made of plastic materials would be really extensive and some literature and reviews already exist, for example the introduced literature in this article, which shows some examples of widespread biogas reactors made of plastics [17-20].

3._ The authors should also outline the characteristics of the manure used for biogas production.

Noted. Please notice the introduced information under 3.2.1 from line 329 to 332 about the Dry Matter and the Volatile Solids of the cattle manure and of the clover grass silage. There is also new information about the biogas composition under 3.2.2, from line 338 to 342 (Figure 7).

4._ The abstract is too generic, include information about study motivation. Although a stirrer is not used and the reason is described it is still not clear how effective mixing is attained.

Ok. Abstract modified with more information, line 19 to 23. The effectiveness of the system (and mixing) is included indirectly; as on one side the biogas yield [NL/kg VS] and the biogas composition have literature values. On the other side, there were problems with the floating layer, the reason why an agitator will be incorporated into the full-scale plant, and also why a vertical hand operated stirrer was introduced into the pilot sized fermenter after the displayed experiment. (please see paragraphs under 3.3.1 and 3.4.1).

5._ Figure 1 is not clear. The digester should be the study focus

Ok, noted. We wanted to focus on all the biogas plant components. The substrate contains lignocellulosic, so that we included in the first representation all the mechanical components that are necessary for the grinding and homogenization of the lignocelluloses (Pretreatment), feeding, heating, supply and circulation of the pilot scale biogas plant. Please also note that the roof of the 3D-representation shows on one hand, that the biogas plant is installed outdoors, and it shields the biogas plant from rain, snow and wind.

6._ How is the substrate fed into the system while keeping it air tight

Right, noted. Please note the paragraphs under 2.1.2 from line 205 to 209. The Pretreatment vessel is connected to the main line of the biogas system circulation loop at the bottom. A ball valve is installed in this outer line at the bottom. If we open the valve for feeding and close it after the procedure letting some liquid on the bottom of the Pretreatment vessel, then we have an air tight feeding.

7._ The authors should present results of biogas compositions is possible.

OK, noted and done! Please see the introduced results under 3.2.2, from line 338 to 342 (Figure 7).

8._ Conclusion should be revised to include study limitations and future prospects.

Ok,  noted. Please see new limitations under Conclusions, from line 484 to 490.

Dear Ms. or Mr. Referee, thank you for your feedback and review! Best Regards

Author Response File: Author Response.pdf

Reviewer 2 Report

1.- I suggest that the authors could add the primary objective described in line 58 of page 2, into the abstract section to clarify their contribution.

2.- Explain how is the treatment of HDPE for creating the textile materials used in the biogas reactor. Also, what does mean in line 106 page 3, the geotextiles word? It is not clear the textile material used for constructing the reactor. Explain, please.

3.- What about the live time for this textile reactor? Where does the HDPE textile material?

4.- Explain deeply how is supplied the absence of a stirrer for the design.

5.- Re-write the idea of line 122 page 3, please. It is not clear.

6.- Describe in the text the Figures 2 and 3.

7.- Additional oxygen for the biogas operation is introduced during the feeding of the system? Explain, please.

8.- The addition of the lifting stirrer was after the obtained results or before? How the results can change with this device?

9.- What about the operation cost and initial monetary inversion for the construction of pilot and high-size plant? Explain deeply.

10.- If you compare the operation, the maintenance, the investment cost, and the operation cost along with the lifetime for this biogas plant regarding the conventional designs using the same level of raw material, who is better? Explain deeply.

Author Response

COMMENTS Referee 2

1.- I suggest that the authors could add the primary objective described in line 58 of page 2, into the abstract section to clarify their contribution.

Ok, done. Please see text between lines 19 to 23. The information is now also included in the abstract.

2.- Explain how is the treatment of HDPE for creating the textile materials used in the biogas reactor. Also, what does mean in line 106 page 3, the geotextiles word? It is not clear the textile material used for constructing the reactor. Explain, please.

Please note the general introduced information between line 110 and 112. Referring to the treatment of HDPE for creating the textile materials used in the biogas reactorà Please note that the composition of the HDPE Materials is not the main issue of this paper. This issue will be handled on another paper/ investigation referring to the properties of the HDPE layer (oxidative properties/ mechanical stress/etc.).

3.- What about the live time for this textile reactor? Where does the HDPE textile material?

Noted. Please see new introduced information and literature under 2, between line 113 and116.

4.- Explain deeply how is supplied the absence of a stirrer for the design.

Ok, noted. Please see notes from line 205 to line 209 under 2.1.2 and under 3.3.1 and 3.4.1.

5.- Re-write the idea of line 122 page 3, please. It is not clear.

Ok, noted and done, thanks!

6.- Describe in the text the Figures 2 and 3.

Ok, noted. Please see the included information from line 145 to line 155 and from line 161 to 163.

7.- Additional oxygen for the biogas operation is introduced during the feeding of the system? Explain, please.

Noted. Please see the explanation of lines 348 and 350.

8.- The addition of the lifting stirrer was after the obtained results or before? How the results can change with this device?

Noted. Please see explanation on lines 382 to 387. The experiment ran without stirrer. After test Day 50 a thick floating layer was removed. The lifting stirrer was introduced after this experiment, and it was operated manually to disrupt the floating layer regularly.

9.- What about the operation cost and initial monetary inversion for the construction of pilot and high-size plant? Explain deeply.

At the moment, there is just an initial theoretical cost calculation of the investment costs of the full-sized demonstration plant. A following article is planned. It will have an overview over the investment costs of the full-sized plant, which is actually in construction. There is no economic analysis of the pilot scale biogas plant, as we wanted to probe the system operation and run the plant with different substrates. We didn´t contemplate the economic viability of the system.

10.- If you compare the operation, the maintenance, the investment cost, and the operation cost along with the lifetime for this biogas plant regarding the conventional designs using the same level of raw material, who is better? Explain deeply.

Ok, noted. The full-sized demonstration plant will be ready in June 2024. After the commissioning, the plant will be operated and evaluated during the course of one year. Other experiments will be done at the same time, which will supply more information about investment, operation and maintenance costs in comparison to conventional materials.

Dear Referee, thank you very much for your feedback and suggestions! Best regards

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript titled "Operation of a Pilot-Scale Biogas Plant Made of Textile Materials and Application of its Results to a Full-Sized Demonstration Plant" explores the operational dynamics of a pioneering biogas plant constructed from textile materials. This innovative approach holds significant promise for revolutionizing biogas production, particularly in the context of small-scale farming operations prevalent in Germany. With an estimated potential of 153 to 187 million tons of fresh matter annually from cattle and pig manure, small farms represent a vital resource for renewable energy production.

This paper delves into the operational intricacies of both pilot-scale and full-sized demonstration biogas plants, constructed using textile materials. By leveraging the insights gleaned from the pilot-scale plant, which featured a 300-liter digester volume and utilized cattle manure and clover grass silage as substrates, the study endeavors to inform the design and implementation of full-scale demonstration plants.

Key considerations include the comparative performance of textile-based biogas reactors against traditional concrete counterparts, the importance of substrate pretreatment, and the design modifications necessary for optimal operation. Additionally, the manuscript sheds light on the regulatory and institutional challenges associated with the approval process for novel biogas plant designs.

The title is concise, informative, and captures the essence of the study.

The abstract provides a clear and succinct summary of the study, including the research question, methodology, key findings, and implications.

The introduction provides a clear and concise overview of the research problem and its significance, effectively setting the context for the study.

The methodology section is well-structured and sufficiently explains the research design, data collection, and analysis procedures.

The results are presented logically and in a visually appealing manner, making it easy to interpret the findings

The discussion provides a comprehensive analysis of the results in light of the research question and relevant literature.

The conclusion effectively summarizes the main findings and their significance in the broader context.

Comments

Line 157: Figure 4 shows the interior of the biogas fermenter of the pilot scale plant. Where is this figure?

Where is the gas storage container in fig 1?, while it already present in fig 2

How is the system discharged?

Please use lowercase letters for the numbers representing the valency of the elements in compounds such as CO₂ and SO₂ throughout the manuscript and in figure ligands.

It is advisable to conduct an economic evaluation of this type of reactor in comparison to traditional models. I believe it may involve significant cost factors, such as the reactor's outer casing and the eccentric pump.

Author Response

Comments Referee 3

1._ Line 157: Figure 4 shows the interior of the biogas fermenter of the pilot scale plant. Where is this figure?

Thank you for this comment. We decided to delete this figure and consequently, the sentence has to be removed.  

2._ Where is the gas storage container in fig 1?, while it already present in fig 2

The 3 D representation shows just the mechanical components in contact with the substrate. Neither the gas, the electrical components, or the heating water loop components are represented in this figure.

3._ How is the system discharged?

Please see lines 148 to 152 and 161 to 163

4._ Please use lowercase letters for the numbers representing the valency of the elements in compounds such as CO₂ and SO₂ throughout the manuscript and in figure ligands.

Ok noted, thanks for the comment. It´s corrected.

5._ It is advisable to conduct an economic evaluation of this type of reactor in comparison to traditional models. I believe it may involve significant cost factors, such as the reactor's outer casing and the eccentric pump.

At the moment the full-sized demonstration plant is being built. So that the determination of the costs is ongoing work. They will be exposed in another coming publication about the Full-Sized Demonstration Plant and it´s application to municipal treatment of separated fraction of food and organic waste.

Dear Reviewer, thank you very much for your feedback! Best Regards

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

All concerns have been addressed.