Software sensors based on titrimetric techniques for the monitoring and control of aerobic and anaerobic bioreactors

Microbial activity influences the vicinity of a microbial cell in a way that changes the pH value of the surrounding medium. Key processes are the production or degradation of charged substances (e.g. volatile fatty acids) and the production of carbon dioxide (or hydrogen carbonate). In a technical system, the shift of the pH value may be prevented by a pH control system. It is proposed in this paper that the resulting base (or acid) consumption rates can be used as input for “software sensors” for substrate and biomass concentrations. This titrimetric technique was successfully applied to extreme thermophilic, aerobic bioprocesses (growth substrates phenol, aliphatic hydrocarbons) for the estimation of biomass and substrate concentrations (formation/degradation rates). In anaerobic experiments, the formation of volatile fatty acids (VFA) was monitored and the reduction of the VFA formation rate in the presence of an inhibitory compound investigated. The results show the versatility of software sensors based on titrimetric techniques and demonstrate the potential for process control in applications in which more sophisticated sensors are not available or affordable.