Robust Control and State Estimation of a Three-Stage Anaerobic Digestion Process

Abstract

The production of biogas via an anaerobic fermentation process is very interesting for various reasons: it not only produces renewable energy, but also facilitates the disposal of organic waste, therefore it preserves the environment, it contributes to the resolution of energy problems in agriculture and agro industry, it’s available for everyone because the waste is available everywhere. This process takes place in continuously stirred tank bioreactor and is described by a highly nonlinear model whose parameters are often uncertain thereby requiring robust control in any process performance enhancement procedure to optimize the biogas production. Thus a robust control technique, synergetic, is proposed to improve the settling time in a fermentation based biogas production in a simulation study; the simulation study is carried out on biotechnological process described by a five-order continuous-time reaction scheme described by three stages. An extended Luenberger observer is proposed under synergetic control to observe the different concentrations because of the high-cost and unavailable measurement instrumentation. The interest of paper lies in controlling the amount of bio methane produced and the observation of all the states of the system (5 different populations of the complex community of bacteria and substrate concentrations acting during anaerobic digestion (AD) processes) by simply measuring the biogas produced. The monitoring, controller and observer performance are evaluated via numerical simulations showing excellent responses under the influence of control input. Key words: Bio methane, anaerobic digestion, synergetic control, extended Luenberger observer, state estimation.