On-line near infrared monitoring of ammonium and dry matter in bioslurry for robust biogas production: A full-scale feasibility study

Heterogeneous substrates fed into agricultural biogas plants originate from many sources with resulting quality fluctuations potentially inhibiting the process. Biogas yield can be substantially increased by optimisation of the organic dry matter load. In this study, near infrared (NIR) spectroscopy was applied on-line in a re-circulating loop configuration operating identically as a full-scale setup. Ammonium could be modelled in the industrially-relevant range 2.42-8.52 g L^-1 with an excellent accuracy and precision, slope ~1.0, r² = 0.97, corresponding to a relative root mean square error of prediction (RMSEP) of 6.7%. Also, dry matter in the similar plant relevant range 5.8-10.8 weight-percent could be predicted with acceptable accuracy (slope ~1.0, r² = 0.83, and a relative RMSEP below 8.0%. Based on these performance characteristics ,it was concluded that NIR spectroscopy can be applied for optimising the efficiency of current and future biogas plants, as well as in biorefinery operations converting heterogeneous bioslurry, energy crops, and wastes into value-added products.