Risk Assessment for Safe Restart of Anaerobic Digestion Processes

For several years, a 1 m fixed bed anaerobic digestion process has been operated for the treatment of wine distillery wastewater. This reactor has been fully instrumented with the following variables available on-line: pH, temperature, liquid and gas flow rates, gas composition (i.e., CH4, CO2 and H2), concentration of bicarbonate, chemical oxygen demand, total organic carbon, volatile fatty acids and partial and total 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 information loss and that of information recovered. It is then used together with a timed automata formalism and model checking capabilities to assess and analyse the induced risk in order to restart the process in safe conditions. Copyright © 2005 IFAC