Transfer of a near infrared spectroscopy laboratory application to an online process analyser for in situ monitoring of anaerobic digestion.

A near infrared (NIR) spectroscopy online process analyser was used for in situ monitoring of anaerobic digestion of energy crops and livestock residues. Spectra were measured on a lab instrument and subjected to piecewise direct standardisation for a spectra transfer. The transfer was used in conjunction with samples for which data was recorded online for the partial least squares regression of volatile solids, ammonium, total inorganic carbon, and volatile fatty acids parameters in the fresh matter of a digester slurry. Validation was performed on independent time series spectra. The results confirmed that the procedure is robust in terms of NIR monitoring of these parameters in order to support the high potential for cross-linking different spectrometers, which may help in making this technology practical.