Construction of an Automated Biochemical Potential Methane (BMP) Prototype Based on Low-Cost Embedded Systems

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this article, a system was developed to measure Biochemical Methane Potential (BMP). The system has control and data acquisition for pressure, temperature, pH, and biogas flow using low-cost embedded systems (such as Arduino). Biogas production was tested in the system using pig manure and sludge from a wastewater plant. The system demonstrated good control of temperature, pH, and biogas measurement. Although the study is interesting, a broader discussion of the results is needed, clarifying aspects of analysis and methods, and demonstrating the advantage of this system over other existing ones. Below is a list of comments and specific questions.

1. In discussion, an analysis of the advantages of this prototype compared to commercial systems is needed, including costs, operational advantages, maintenance, and other aspects. What advantages does this system have over the AMPTS® III from Bioprocess Control Sweden AB or the RESPIROMETRIC Sensor System 6 Maxi – BMP from Velp?
2. The system does not have an agitation system, which severely limits the types of substrates that can be tested. It is recommended to include this aspect in the discussion section when analyzing the advantages and disadvantages of the system compared to existing ones.
3. The pH regularly tends to become alkaline. Why does the pH remain below 7 at the end of the process?. Did you take measurements with an external potentiometer to corroborate the pH measurements?.
4. What was the alkalinity? This parameter is very important for anaerobic digestion.
5. Figure 19. What is the composition of the biogas, the percentage of CO₂ and methane? How do you ensure that what was produced is methane?
6. What was the purpose of using two systems (pressure and flow sensors) to measure biogas production?. Which is better, in terms of cost or robustness? It is not advisable to have two systems installed for the same purpose; one must be chosen.
7. Results were included in the discussion section; a clear separation between the two sections should be made.
8. Indicate in Figure 1b the meaning of LS1, TS1, P1, TK1, etc.
9. Indicate what these terms are in the equations used.
10. Include a description of Figure 4.
11. Insert the meaning of each parameter in Table 4.
12. Figure 16. What model did you use to obtain the theoretical data?
13. Lines 249-252 should be in the methods section.
14. Lines 264-271 are duplicated; they are the same as lines 256-263.

Author Response

Comment 1: In discussion, an analysis of the advantages of this prototype compared to commercial systems is needed, including costs, operational advantages, maintenance, and other aspects. What advantages does this system have over the AMPTS® III from Bioprocess Control Sweden AB or the RESPIROMETRIC Sensor System 6 Maxi – BMP from Velp?

Response 1: The comparison between the prototype and commercial systems is not straightforward, as it largely depends on the specific operating conditions and, above all, on the characteristics of the biomass being tested. In general terms, however, the prototype shows a more limited scope of use compared to the selected alternatives, mainly due to its simpler system for gas collection, storage and data analysis. Furthermore, while the commercial systems employ sensors specifically designed to ensure high-quality operation under standardized conditions, the prototype relies on more basic and accessible sensors that, although functional, are not necessarily specialized for biogas applications.

In the following Table [45], [46], [47], [48], some differentiating points can be identified regarding the scope of the commercial products compared.

 

Feature	Prototype	AMPTS® III (Bioprocess Control)	RESPIROMETRIC Sensor System 6 Maxi – Velp
Number of reactors	3 (2 L each one)	18 reactors standard, 9 in Light version	6 equipped with sensors
Temperature control precision	Experimental results show that temperature varies ±2 °C	±0.2 °C precision reported for AMPTS III	±1 °C or ±0.5 °C (at 20°C) in Velp systems
Pressure/Measurement range	The pressure sensors were calibrated over a "global range" of 0 to 15 psig	The equipment is not designed to work with high pressures, it can operate under pressure variations of -0.5 to 0.5 mbar	Pressure range 500-2000 mbar (hPa)
User-interface / data acquisition	Simple data collection system	Aurora™ is built-in software accessible through a web browser on any device. It features a new interface with enhanced functions such as starting and stopping all channels, zooming on graphs, flexible gas normalization, phased agitation control, and raw data download.	Velp has proprietary software (RESPIROSoft™), real-time curve display and wireless DataBox
Mixing / stirring	No mixing	AMPTS III includes mechanical agitation	Velp Maxi: uses bottles and may include stirring station

 

Comment 2: The system does not have an agitation system, which severely limits the types of substrates that can be tested. It is recommended to include this aspect in the discussion section when analyzing the advantages and disadvantages of the system compared to existing ones.

Response 2: In substrates that are dilute and already well dispersed, mechanical mixing may provide little additional benefit. Rojas and company [49] reported that in highly diluted media, the contact between bacteria and substrate was sufficient without mixing, achieving similar yields to agitated systems as long as the inoculum was active and capable.

Although literature indicates that agitation can be omitted in systems with dissolved or well-dispersed biomass, it would still be ideal to compare biogas production with and without mixing in the prototype. This comparison would provide a clearer understanding of the process dynamics and confirm whether the absence of agitation affects performance under the specific operating conditions of the system.

 

Comment 3: The pH regularly tends to become alkaline. Why does the pH remain below 7 at the end of the process?. Did you take measurements with an external potentiometer to corroborate the pH measurements?

Response 3: The BMP test does not result in a neutral or slightly alkaline pH at the end, this may indicate that the digestion process was not fully balanced. This could happen if the microorganisms were unable to completely convert the intermediate products into methane, leaving residual compounds that affect the pH. Checking with a potentiometer would be ideal to confirm the data.

 

Comment 4: What was the alkalinity? This parameter is very important for anaerobic digestion.

Response 4: In this prototype, alkalinity was not measured because the main objective was to demonstrate the system’s capacity to monitor and quantify methane production accurately. The focus was placed on key variables such as temperature, pH, pressure and gas flow, which are essential for BMP determination. Although alkalinity is an important indicator of buffering capacity and process stability, it was excluded to keep the design simple and low-cost. Future versions of the system may include alkalinity monitoring to provide a more complete evaluation of reactor performance.

 

Comment 5: Figure 19. What is the composition of the biogas, the percentage of CO₂ and methane? How do you ensure that what was produced is methane? How do you ensure that what was produced is methane?

Response 5: We have added to the Materials and Methods section the análisis of biogas. Daily samples were collected from the headspace of the reactors and analysed by gas chromatography (GC) using an Agilent 6890A system (Agilent Technologies) equipped with HP-PLOT/Q and HP-MOLSIEVE columns, in order to determine the concentrations of methane (CH₄), carbon dioxide (CO₂), and other trace gases [26].

 Furthermore, the explanatory text preceding Figure 19 has been revised and improved to provide a clearer description of the results. The biogas production was measured continuously using two methods. The first one was an indirect method, calculated through the reactor pressure. This pressure can be transformed to standard volume using the combined gases law. The values of biogas were corrected to standard temperature and pressure (STP) conditions (25 °C and 100 kPa). The second one was a direct method. The level sensor shown in Figure 19, which uses the ‘tipping bucket’ principle, was used. The liquid is displaced by the biogas in a specially designed chamber. The accumulated biogas production is shown for each reactor in Figure 19. A similar behaviour of accumulated methane production in the three reactors can be observed. However, after 25000 minutes, when the production start to decrease, the three tests show little difference.

 

Comment 6: What was the purpose of using two systems (pressure and flow sensors) to measure biogas production?. Which is better, in terms of cost or robustness? It is not advisable to have two systems installed for the same purpose; one must be chosen.

Response 6: The use of both pressure and flow sensors was mainly driven by the availability of accessible and low-cost instrumentation, which made it feasible to implement both approaches in the prototype. The pressure sensor was used to quantify the produced gas volume, while the flow sensor provided an alternative measurement, allowing comparison between the two methods. This dual approach was not intended as a permanent design choice but rather as a way to evaluate performance and consistency. In practice, a single system would be sufficient, and the decision between them would depend on balancing cost, robustness, and the specific requirements of the application.

 

Comment 7: Results were included in the discussion section; a clear separation between the two sections should be made.

Response 7: The separation between the results and discussion sections was revised to incorporate adjustments suggested during the feedback process.

 

Comment 8: Indicate in Figure 1b the meaning of LS1, TS1, P1, TK1, etc.

Response 8: The acronyms R1, R2, and R3 correspond to the three reactors; LS and TS denote the level switch and the temperature switch, respectively; TK1 identifies Tank 1; and P1 refers to Pump 1.

 

Comment 9: Indicate what these terms are in the equations used.

Response 9: The terms used in the equations represent the readings from the temperature and level transmitters, while the others are only intended to identify the system components.

 

Comment 10: Include a description of Figure 4.

Response 10: illustrates the configuration of the control and power system. At the top, the connection of the pump motor along with its respective protective devices is presented. On the right-hand side, the single-line diagram of the alternating current supply system is shown, together with the corresponding AC–DC converters. In the central section, the high-level control unit implemented through a Raspberry Pi board is displayed on the left, while on the right, the data acquisition system managed by an Arduino ATMEGA board is depicted. At the bottom, the connection of the pH meter is indicated. Surrounding the data acquisition system, the figure also details each of the sensors integrated into the system.

 

Comment 11: Insert the meaning of each parameter in Table 4.

Response 11: We suggest reviewing the abbreviations section that we have completed with this information.

 

Comment 12: Figure 16. What model did you use to obtain the theoretical data?

Response 12: The theoretical data presented in Figure 16 were obtained by solving Equation (9), which corresponds to the energy balance for the jacket design as shown in the materials and methods section. In the revised version, we clarified that the continuous line represents the theoretical values calculated from Equation (9), while the dots correspond to the experimental measurements. Thank you for pointing this out.

 

Comment 13: Lines 249-252 should be in the methods section. The description of the mixture preparation and monitoring conditions has been relocated to the Materials and Methods section as suggested. Based on these values, the mixture was prepared with 178 g of pig manure, 107 g of WWTP sludge, and 1.215 g of water to fill 90% of the reactor volume. Throughout the test, pH, temperature, flow, and pressure were continuously monitored.

Response 13: The description of the mixture preparation and monitoring conditions has been relocated to the Materials and Methods section as suggested. Based on these values, the mixture was prepared with 178 g of pig manure, 107 g of WWTP sludge, and 1.215 g of water to fill 90% of the reactor volume. Throughout the test, pH, temperature, flow and pressure were continuously monitored. Thank you for pointing this out.

 

Comment 14: Lines 264-271 are duplicated; they are the same as lines 256-263.

Response 14: We thank the reviewer for pointing this out. The paragraph describing Figure 19 in lines 264–271 has been adjusted. The biogas production was measured continuously using two methods. The first one was an indirect method, calculated through the reactor pressure. This pressure can be transformed to standard volume using the combined gases law. The values of biogas were corrected to standard temperature and pressure (STP) conditions (25 °C and 100 kPa). The second one was a direct method. The level sensor shown in Figure 9, which uses the ‘tipping bucket’ principle, was used. The liquid is displaced by the biogas in a specially designed chamber. The accumulated biogas production is shown for each reactor in Figure 19. A similar behaviour of accumulated methane production in the three reactors can be observed. However, after 25000 minutes, when the production start to decrease, the three tests show little difference.

Reviewer 2 Report

Comments and Suggestions for Authors

1) “WWTP” is defined as “Water Waste Treatment Plant” in the Abbreviations section——I suggest that the authors can use “Wastewater Treatment Plant” instead of “Water Waste Treatment Plant”.

2) “PLC” is first mentioned as “Programmable Logic Controller” in Section 2.3——I suggest that it can be defined earlier in the Introduction.

Author Response

Comment 1: “WWTP” is defined as “Water Waste Treatment Plant” in the Abbreviations section——I suggest that the authors can use “Wastewater Treatment Plant” instead of “Water Waste Treatment Plant”.

Response 1: The abbreviation has been corrected, and “Wastewater Treatment Plant” is now consistently used throughout the manuscript in abbreviation section. Thank you for pointing this out. 

 

Comment 2: “PLC” is first mentioned as “Programmable Logic Controller” in Section 2.3——I suggest that it can be defined earlier in the Introduction.

Response 2: The requested modification has been implemented and the corresponding clarification has been added at the end of the introduction. “This study presents the design and construction of an automated BMP measurement prototype developed at UPB, which integrates a Programmable Logic Controller (PLC) to enable real-time monitoring, control, and data acquisition”. Thank you for pointing this out.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript describes a low-cost anaerobic digestion (AD) prototype designed for Biochemical Methane Potential (BMP) testing. The system integrates sensors for monitoring critical parameters such as pH, temperature, and biogas flow, and it uses accessible Arduino and Raspberry Pi controllers connected through PLC loops to regulate the operating conditions. The authors aim to provide a practical and affordable platform for BMP testing that could help improve standardization across laboratories. The study expands on the preexisting work in the field and is of practical interest to the readers.

1. Please include a short review of the existing BMP measurement systems, both commercial and open-source. It would be helpful to clearly explain how your design differs from these prior systems and what specific advantages or innovations it offers. A table outlining the commonly observed drawbacks of the existing system and the potential benefits of the proposed system would be beneficial.
2. Did you run positive and negative controls for the prototype, particularly for validating the gas flow meter? Since biogas typically contains not only methane but also CO2 and H2S, please describe how these gases were accounted for in your measurements and whether corrections were made in the reported BMP values.
3. Was a calibration study performed on the flow meter before use in the BMP trials? If yes, please provide details of the calibration procedure, including the range tested, accuracy, and error margins. This is important to evaluate the reliability of your gas quantification.
4. Line 209 states that pH was controlled using 5 M NaOH, while Line 254 mentions pH calibration with 1 M NaOH. Please clarify which concentration was actually used and ensure this is consistent throughout the manuscript.
5. The decision not to mix pig manure during the BMP test requires further justification. Given the potential for settling and stratification, please provide evidence that mass transfer and hydrolysis were not impaired, and whether you considered comparing with a gently mixed setup?
6. In Line 276, you mention that the results were statistically significant compared to previously published data. Please explain which statistical test was applied. Also, specify how many reactors were run in parallel or series, and include error bars on all relevant figures to better reflect variability.
7. The author is recommended to explain the methodology and experimental setup for the study more comprehensively.

Author Response

Comment 1: Please include a short review of the existing BMP measurement systems, both commercial and open-source. It would be helpful to clearly explain how your design differs from these prior systems and what specific advantages or innovations it offers. A table outlining the commonly observed drawbacks of the existing system and the potential benefits of the proposed system would be beneficial.

Response 1: The Table below summarizes some of the most widely recognized methods for determining BMP, noted for their impact, scope and replicability.

 

Method	Main elements	Limitations
Classical batch test [21]	It was a foundational method for BMP analysis. It is simple and low cost, uses sealed reactors and allows measurement of both total biogas and its methane content	It shows high variability, lacks standardized control criteria and is therefore difficult to compare across laboratories
Angelidaki and company control reactor [8]	It can be considered the basis for international harmonization of the BMP protocol. Applicable to both solid and liquid wastes, includes a defined inoculum-to-substrate ratio, blanks and positive controls, mesophilic incubation, mixing and standardized gas measurement	It is not an official standard and has therefore been only partially adopted by laboratories
VDI 4630 [20]	A recognized and reproducible standard, widely applied in Europe. Its rigorous technical framework, defines reactor volume, number of replicates, temperature, termination criteria, blanks and control	Complex technical approach, paid document, and less accessible outside Germany
Holliger and company [18]	International consensus document that provides inter-laboratory quality improvement. It includes mandatory controls, standardization for volatile solids, correction for inoculum production and stabilization criteria	It is not intended to replace or rewrite the standard. It is used as a guide and not as a legal standard

 

The system offers several advantages over traditional methodologies used to determine BMP. Being an automated, low-cost prototype, it facilitates the measurement process and reduces the need for manual labor compared to protocols such as the VDI 4630 standard, which are typically more expensive and complex. The incorporation of pressure, temperature, pH and biogas flow sensors also allows for real-time monitoring of digestion conditions, representing a significant advance over the classic Owen and company method and responding to Angelidaki and Holliger's recommendations regarding the control of critical variables. Furthermore, the built-in heat exchanger allows for rapid and stable achievement of mesophilic conditions, reinforcing the system's reliability.

Still, the prototype has some clear limits. Unlike well-established protocols, it has not been tested across different laboratories, which means its results cannot yet be compared with confidence. Its small scale, using only three two-liter reactors, also weakens the strength of the tests and makes the data less representative. In addition, because it is not officially recognized as a standard, unlike VDI 4630, it carries no regulatory weight. Also, the system does not include some key methodological steps described in the guidelines of Angelidaki and Holliger, such as setting the right inoculum-to-substrate ratio, adding proper controls, and defining clear criteria for when the tests should end. Thank you for pointing this out.

 

Comment 2: Did you run positive and negative controls for the prototype, particularly for validating the gas flow meter? Since biogas typically contains not only methane but also CO2 and H2S, please describe how these gases were accounted for in your measurements and whether corrections were made in the reported BMP values.

Response 2: The gas flows were measured using a mass flow meter (PerkinElmer, FMA) in order to validate the performance of the prototype. The results obtained showed an error of less than 5% as we mentioned in the document when compared with the prototype’s measurements, which we consider acceptable for this type of test.  Thank you for pointing this out.

 

Comment 3: Was a calibration study performed on the flow meter before use in the BMP trials? If yes, please provide details of the calibration procedure, including the range tested, accuracy, and error margins. This is important to evaluate the reliability of your gas quantification.

Response 3: In our study, both flow measurement methods implemented in the prototype—pressure-based and siphon-based displacement—were verified against a mass flow meter (PerkinElmer, FMA). The comparison demonstrated an error margin below 5%, which confirmed the consistency and reliability of the prototype’s measurements within the expected operating range. While no independent calibration curve was developed beyond this verification, the use of a reference mass flow meter ensured traceability and accuracy of the gas quantification. This approach aligns with common practice in BMP studies, where relative performance and reproducibility are prioritized for prototype validation. In addition, Koch and company reported less than 5% difference between manometric and gravimetric methods [34], as we mentioned in lines 162 to 166. Thank you for pointing this out.

 

Comment 4: Line 209 states that pH was controlled using 5 M NaOH, while Line 254 mentions pH calibration with 1 M NaOH. Please clarify which concentration was actually used and ensure this is consistent throughout the manuscript.

Response 4: The correct concentration is 1 M NaOH, and this has now been amended to ensure consistency throughout the manuscript. Thank you for pointing this out.

 

Comment 5: The decision not to mix pig manure during the BMP test requires further justification. Given the potential for settling and stratification, please provide evidence that mass transfer and hydrolysis were not impaired, and whether you considered comparing with a gently mixed setup?

Response 5: In the present study, pig manure was selected as the substrate, which is one of the most widely studied feedstocks for anaerobic digestion and therefore provides a reliable benchmark for prototype evaluation. For this specific case, the BMP tests were conducted without mixing in order to maintain simplicity of operation and reduce mechanical interventions, while still ensuring conditions comparable with several standard BMP protocols reported in the literature. We acknowledge that the absence of mixing may influence hydrolysis rates in substrates prone to settling or stratification; however, pig manure has been extensively validated in similar setups, supporting the robustness of the results obtained here. We also recognize the importance of exploring other substrates with different rheological properties under both static and mixed conditions, as this would allow us to further demonstrate the reliability and broader applicability of the prototype. Thank you for pointing this out.

 

Comment 6: In Line 276, you mention that the results were statistically significant compared to previously published data. Please explain which statistical test was applied. Also, specify how many reactors were run in parallel or series, and include error bars on all relevant figures to better reflect variability.

Response 6: The statistical comparison was performed using a two-tailed Student’s t-test at a 5% significance level. For the BMP assays, three reactors were run in parallel under identical conditions, and the results are presented as mean values. We acknowledge the reviewer’s suggestion and will include error bars in the relevant figures to better illustrate data variability and improve clarity. Thank you for pointing this out.

 

Comment 7: The author is recommended to explain the methodology and experimental setup for the study more comprehensively.

Response 7: The methodology was reconstructed in a simpler and more straightforward way to facilitate understanding. Thank you for pointing this out.

Reviewer 4 Report

Comments and Suggestions for Authors

This paper presents the development of an automated BMP (Biochemical Methane Potential) testing system designed for anaerobic digestion research. The authors constructed a prototype using low-cost embedded systems (Arduino Mega 2560 and Raspberry Pi 3) to control three 2-liter reactors with integrated temperature control, biogas quantification, and data acquisition capabilities. The system was validated through a 22-day test using pig manure as substrate and municipal wastewater sludge as inoculum, achieving methane yields of 447 LCH₄/kgVS. The work addresses a relevant need in anaerobic digestion research by developing an accessible automation solution for BMP testing. The engineering approach demonstrates solid technical competence, particularly in thermal system design and sensor integration. The open-source philosophy and use of readily available components make this potentially valuable for laboratories with limited resources. However, several methodological aspects would benefit from strengthening to enhance the system's reliability and broader applicability. The work represents a valuable contribution to making BMP testing more accessible, and addressing these points would significantly strengthen its impact and adoption potential. Please find my comments below :

• Lines 272-277 : Could the authors provide more comprehensive validation data comparing their system with established commercial BMP equipment? The single substrate test limits confidence in system performance across different waste types.
• Lines 259-263: The reported ±5°C fluctuations around the setpoint exceed typical BMP requirements. What modifications could improve temperature stability to ±2°C as recommended by standard protocols?
• Lines 64-66 : The decision to omit mixing appears to limit applicability to certain substrates. How might this affect reproducibility with more complex or heterogeneous materials?
• Lines 145-147 : The use of different equations for pressure sensor calibration across ranges needs better justification. What validation was performed to ensure accuracy across the full measurement range?
• How closely does the testing protocol align with established BMP standards ? Any deviations should be clearly justified.
• Lines 68-69 : Claims about scaling to 15 reactors would be strengthened by theoretical analysis or preliminary testing of system capacity limits.

Author Response

Comment 1: Lines 272-277. Could the authors provide more comprehensive validation data comparing their system with established commercial BMP equipment? The single substrate test limits confidence in system performance across different waste types.  

Response 1: A study carried out in Colombia on pig manure reported values close to 437 LCH4/kg VS, similar to those obtained with the prototype. This evidence shows that the results are not only statistically robust but also comparable with other studies [42]. Likewise, another study reported ranges of 0.29 - 0.53 m³ CH4/kg VS depending on biomass type and experimental conditions, which further supports the similarity of the study’s results [43]. We agree that a broader validation against commercial BMP equipment, including multiple substrates, would further strengthen confidence in the system’s performance. In this study, however, validation was carried out for a specific substrate as a first step, which was consider relevant for demonstrating the functionality of the prototype. Thank you for pointing this out. Lines 322-330.

 

Comment 2: Lines 259-263. The reported ±5°C fluctuations around the setpoint exceed typical BMP requirements. What modifications could improve temperature stability to ±2°C as recommended by standard protocols?

Response 2: In our setup, the setpoint was fixed at 37 °C, and the temperature varied within the range of 35–40 °C, corresponding to a fluctuation of approximately ±2.5 °C. This variation resulted from the use of an on/off control strategy programmed in PLC1, which helped minimize mechanical stress on the pump, the system’s main actuator. We acknowledge that a PID-based control strategy would provide tighter regulation and enable compliance with the ±2 °C margin recommended in standard BMP protocols (e.g., VDI 4630; Angelidaki and company, 2009). We consider this a valuable improvement to be incorporated into future developments of the prototype, where additional strategies, such as lowering the tank setpoint temperature and increasing the pump activation frequency, could also be implemented to further enhance thermal stability. Thank you for pointing this out. Lines 298-305.

 

Comment 3: Lines 64-66. The decision to omit mixing appears to limit applicability to certain substrates. How might this affect reproducibility with more complex or heterogeneous materials?

Response 3: The Prototype was intentionally developed for diluted or readily degradable substrates, where previous studies have shown that mixing is not essential. However, is known that for more complex or heterogeneous materials, the lack of agitation could influence both degradation efficiency and reproducibility. As part of future developments, we are conducting tests with magnetic stirrers placed at the bottom of the reactors, combined with magnetic bars inside, to provide effective mixing. This approach is being explored as a modular and optional system to extend the range of substrates that can be reliably tested, while maintaining the low-cost and scalable features of the prototype. Thanks for mentioning it. We have added the observation at the end of the discussion section, on Lines 348-356.

 

Comment 4: Lines 145-147. The use of different equations for pressure sensor calibration across ranges needs better justification. What validation was performed to ensure accuracy across the full measurement range? 

Response 4: The use of two calibration equations was adopted to address differences in sensor response across the measurement range. Equation (11) was applied for pressures between 0–3 psig, while Equation (12) was used for the 3–15 psig range. Based on prior experience with similar calibration approaches, this method provides a reliable way to validate sensor performance. Validation against a trusted reference confirmed that the measurements stayed within acceptable limits, ensuring consistency and reliability of the data throughout the experiments. Thank you for pointing this out.

 

Comment 5: How closely does the testing protocol align with established BMP standards ? Any deviations should be clearly justified.

Response 5: The testing protocol follows the main principles of established BMP procedures, such as controlled conditions, monitoring of key parameters, and use of standard calculations for methane yield. Its main strength lies in its simplicity and ease of replication, which makes it accessible for broader application. The main deviation is that it has not yet undergone interlaboratory validation, which is a feature of more consolidated standards. While this limits direct comparability at present, the protocol provides a solid and practical framework that can be further refined and validated in future studies. Thank you for pointing this out.

 

Comment 6: Lines 68-69 claims about scaling to 15 reactors would be strengthened by theoretical analysis or preliminary testing of system capacity limits.

Response 6: The affirmation is supported by prior experience with similar modular systems, in which performance remained consistent as additional units were incorporated. Although a formal capacity analysis has not yet been conducted, the prototype was designed with scalability in mind, particularly regarding heat exchanger capacity and system integration. These design principles indicate that expansion to 15 reactors is technically feasible. We recognize, however, the importance of confirming this through dedicated tests, which we identify as a realistic and necessary next step to validate scalability under operating conditions. We appreciate the observation.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

El manuscrito fue mejorado, los autores atendieron las observaciones.