Fast measurement of bio- chemical methane potential (BMP) by NIRS

Significance of the Topic

Determination of biochemical methane potential (BMP) is essential for optimizing anaerobic digestion processes in biogas production. Conventional BMP testing requires 30–40 days, limiting its use as a real-time management tool. Near-infrared spectroscopy (NIRS) coupled with a robust calibration model offers rapid, chemical-free assessment of BMP, enabling operators to adjust feedstocks and process conditions for improved methane yields within minutes.

Objectives and Study Overview

This application note evaluates the performance of a combined solution consisting of the Metrohm NIRS DS2500 analyzer and the Ondalys Flash BMP® calibration model. The goal was to verify accuracy, precision, and speed of BMP predictions on a diverse set of organic substrates compared to the reference fermentation method, and to demonstrate practical benefits for process monitoring and optimization.

Methodology and Instrumentation

The calibration model was developed by Ondalys in collaboration with Veolia and INRA-LBE, based on approximately 500 samples spanning agro-industrial waste, biowaste, energy crops, agricultural residues, fatty waste, plants, sewage sludge, and digestate. Reference BMP values followed the Angelidaki et al. (2009) protocol.

• Analyzer: Metrohm NIRS DS2500
• Sample accessory: DS2500 sample cup
• Software: Vision Air with imported Flash BMP® calibration
• Calibration range: 20–700 mL CH₄·g⁻¹ VS
• Model accuracy: 15–20 % deviation
• Model validity across multiple substrate categories

For validation, ten substrates (manure, energy crops, cereals, oil, mixed residues) yielding 209–443 mL CH₄·g⁻¹ VS were frozen, dried, ground, and scanned in diffuse reflectance mode. BMP predictions were generated in under one minute per sample without chemical reagents.

Main Results and Discussion

Comparison with reference values showed strong agreement. Key performance metrics included:

• Standard Error of Prediction (SEP): 14.3 mL CH₄·g⁻¹ VS
• Root Mean Square Deviation (RMSD): 14.8 mL CH₄·g⁻¹ VS
• Individual sample deviation: 0.5–8.8 %

These results match the precision of the conventional assay but deliver outcomes in minutes rather than weeks. The NIR spectra provided by Vision Air allow quick identification of outliers and monitoring of substrate variability.

Benefits and Practical Applications

Implementing this NIR-based BMP determination enables:

• Rapid decision-making for feedstock selection and mixture ratios
• Real-time process control to maximize methane yield
• Reduced laboratory workload and elimination of chemical reagents
• Cost savings through faster turnaround and lower operational expenses

Future Trends and Potential Applications

Advances in NIR instrumentation, machine learning algorithms, and expanded calibration libraries will further enhance prediction accuracy and extend applications to co-digestion strategies. Integration with online monitoring systems and automation can deliver continuous BMP assessment, paving the way for fully adaptive biogas production facilities.

Conclusion

The Metrohm NIRS DS2500 coupled with the Ondalys Flash BMP® model provides a reliable, fast, and reagent-free alternative to conventional BMP testing. Validation across diverse substrates demonstrates comparable accuracy and significant time savings, supporting effective process optimization in biogas plants.

Reference

• Angelidaki, I., Alves, M., Bolzonella, D., Borza, L., Campos, J.L., Guwy, A.J.,…”Standardization of methods for the purification and measurement of biochemical methane potential (BMP) of solid organic wastes.” Water Science and Technology, 2009.