The paper deals with experimental studies and software sensor design for anaerobic digestion of cattle dung in a pilot plant. Software sensors for acidogenic and methanogenic bacterial concentrations and specific growth rates have been designed based upon a three-stage anaerobic digestion model, and mathematical tools stemming from differential algebra. For the first time in the known literature, they allow estimation of bacterial concentrations without having recourse to the time and resource consuming stage of bacterial specific growth rate empirical modeling. The proposed software sensors use only online values of the dilution rate, and biogas flow rate together with methane and carbon dioxide percentage in the biogas. Therefore they are simple, and easy to implement. Potential usages of the proposed software sensors are on-line monitoring (which is very useful for stable operation of industrial biogas plants) of anaerobic digestion processes, and implementation of sophisticated control strategies.
