  We consider the chemostat model with the substrate concentration as the
single measurement. We propose a control strategy that drives the system at a
steady state maximizing the gas production without the knowledge of the
specific growth rate. Our approach separates the extremum seeking problem from
the feedback control problem such that each of the two subproblems can be
solved with relatively simple algorithms. We are then free to choose any
numerical optimization algorithm. We give a demonstration for two choices: one
is based on slow-fast dynamics and numerical continuation, the other is a
combination of golden-section and Newton iteration. The method copes with
non-monotonic growth functions.
