“…there is r * ∈ (0, 1) such that for any r ∈ (r * , 1), the maximum, relative to D, of G 2 (S in , D, r) will be larger than the maximum G(S in , D). Here G 2 (S in , D, r) is the biogas flow rate of the serial configuration at steady state E 2 and G(S in , D) is the biogas flow rate of the single chemostat, see [1,3]. This result was obtained by showing that the first partial derivative in r = 1 (at left) of…”