Hyperspectral sensing techniques for mesophilic anaerobic reaction monitoring and control

An anaerobic digestion process, finalized to biogas production, is characterised by different steps, each involving the variation of some chemical and physical parameters related to the presence of some specific mass fractions as: pH, Chemical Oxygen Demand (COD), Volatile Solids (VS), Nitrate (NO3-) and Phosphate (PO3-). A correct process characterization thus requires a periodical sampling of the organic mixture present in the reactor and a further analysis of the samples adopting traditional physical-chemical methods. Such an approach is discontinuous, time consuming and expensive and, for its characteristics, does not allow a continuous monitoring of the solids fractions, not only in terms of composition, but also in terms of homogeneity. In this paper the possibilities offered by a new analytical approach based on HyperSpectral Imaging (HSI) are investigated and critically evaluated. The application of the proposed technique is addressed to identify the possible correlation existing, in terms of quality and reliability of the results, between the “classical” discontinuous chemical-physical approaches and the HSI based ones. Results based on NIR-HSI analysis and PCA show a strong correlation with classical collected data. Modelling procedures have been developed to help in waste recipes formulation and bioreactors control.