The benefits of upgrading extremum-seeking controllers with an effective exploitation of the buffer capacity of equalization tanks have been investigated and applied to anaerobic digesters. In this respect, a Fuzzy-based supervisory module that monitors the state of the equalization tank has been designed and built on top of an extremum-seeking algorithm in charge of automatically regulating the wastewater fed into the anaerobic digester. The extremum-seeking controller guarantees good disturbance rejection and methane production around an upper limit set-point. The on-top Fuzzy module optimizes the long-term methane production by modifying this upper limit set-point as a function of the state of the equalization tank. A systematic simulation study has been carried out to evaluate the performance of the proposed control solution. Thus, on the basis of existing simulation benchmarks for assessment of control strategies in wastewater treatment plants, a dedicated simulation protocol for anaerobic digesters has been defined and implemented. Simulation results have shown that, compared with manual operation, effluent quality and methane production improvements of 10–15% are achieved using the proposed control approach.
Keywords: anaerobic digestion, automatic control, extremum-seeking, fuzzy logic, simulation