The potential for online monitoring of short-term process dynamics in anaerobic digestion using near-infrared spectroscopy

This work reports the development of a near-infrared (NIR) spectroscopy online calibration for monitoring volatile solids (VS) and total volatile fatty acids (VFA) process parameters during anaerobic digestion (AD). The objective was to investigate its potential to estimate the dynamics of AD process parameters after feeding events. A recirculation loop was employed to record online measurements during an eight-month experiment using a 3.3 m3 pilot plant fed with maize silage under mesophilic conditions. Sampling was performed to conduct calibrations and subsequent test-set validations, comparing the NIR spectroscopy estimates to the reference values. The calibrated accuracy in terms of mean prediction errors (RMSEP) was 3 g kg−1 for VS and 0.9 g kg−1 for VFA in the fresh matter. By applying the calibrations to time series spectra, the model accuracy provided adequate indications of the concentration changes, including highly sensitive monitoring of short-term VFA dynamics.

► NIR spectroscopy allows online-monitoring of short-term concentration changes of VS and VFA.
► Estimates show a precise increase in the VFA concentration at an early stage.
► The VFA concentration can be independently being estimated from the VS content.
► NIR spectroscopy supports for an optimized process operation of biogas digesters.