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

Significance of the Topic

Biochemical methane potential (BMP) is a critical metric for evaluating the degradability of organic substrates in anaerobic digestion. Conventional BMP assays require 30–40 days of incubation, limiting their utility for process control and substrate screening. Rapid determination of BMP using near-infrared spectroscopy (NIRS) enables timely decisions to optimize biogas production and increase methane yield without long delays or chemical reagents.

Objectives and Study Overview

This application note presents a fast BMP measurement approach that combines the Metrohm NIRS DS2500 analyzer with Ondalys Flash BMP calibration model. The goal is to assess the accuracy and robustness of the NIR-based method across diverse substrates commonly used in biogas plants, demonstrating an alternative to time-intensive fermentation assays.

Methodology and Instrumentation

Sample Preparation:

• A set of approximately 500 reference samples covering agro-industrial waste, biowaste, energy crops, agricultural residues, fats, sludge and digestate was used to build the calibration model.
• For validation, ten substrates with reference BMP values between 209 and 443 mL CH4 per g volatile solids (VS) were frozen, freeze-dried and ground to ensure homogeneity.

Calibration Development:

• NIR spectra were recorded on Metrohm NIRS DS2500 across the relevant spectral range.
• Partial least squares (PLS) regression was applied to relate spectral features to reference BMP values obtained by standard fermentation (Angelidaki et al., 2009).

Validation Procedure:

• The Flash BMP model was imported into Vision Air software for prediction of unknown samples.
• Predicted BMP values were compared against reference measurements to evaluate prediction error and model reliability.

Main Results and Discussion

Validation results for ten substrates showed:

• Standard error of prediction (SEP): 14.3 mL CH4 per g VS
• Root mean square error of prediction (RMSEP): 14.8 mL CH4 per g VS
• Individual deviations ranged from 0.5 % to 8.8 % relative to reference values

These metrics confirm that the NIR-based method achieves accuracy comparable to the conventional BMP assay while delivering results within one minute per sample. The broad substrate range and calibration validity demonstrate the model’s applicability to various waste streams.

Benefits and Practical Applications

This rapid NIRS-based BMP approach offers:

• Significant time savings: results in minutes versus weeks
• Chemical-free analysis: no reagents required
• High throughput: enables screening of multiple substrates in routine operations
• Process optimization: real-time data supports feedstock selection and digester management

Future Trends and Potential Applications

Emerging opportunities include:

• Expansion of calibration libraries to cover novel feedstocks and co-substrates
• Integration with digital monitoring platforms and predictive process control
• On-line or in-line NIR probes for continuous BMP monitoring
• Application of machine learning to refine model accuracy and adaptability

Conclusion

The combination of Metrohm NIRS DS2500 and the Ondalys Flash BMP calibration model provides a rapid, reliable and reagent-free method for determining biochemical methane potential. Its high accuracy and speed support effective biogas plant management and substrate screening, offering a practical alternative to traditional BMP assays.

References

Angelidaki, I. et al. (2009) Standard Method for Biochemical Methane Potential (BMP) Assay. International Journal of Biogas Research.