Risk Assessment for Safe Restart of Anaerobic Digestion Processes

For several years, a 1 m3 fixed bed anaerobic digestion process has been operated for the treatment of wine distillery vinasses. This reactor has been fully instrumented with the following variables available on-line: pH, temperature, liquid and gas flow rates, gas composition , concentration of bicarbonate, chemical oxygen demand, total organic carbon, volatile fatty acids and alkalinity. This paper deals with the problem of restarting the reactor after a period of time with missing information from the sensors. An approach has been developed to determine – while managing inherent uncertainty – the evolution of the inputs between the date of loss of information and the one when the information is recovered. It is then used together with a timed automata formalism and model checking capabilities to assess and to analyse the induced risk in order to restart the process in safe conditions.