Effect of the S0/X0 ratio on energy uncoupling in substrate-sufficient batch culture of activated sludge

A batch culture of microorganisms can be classified to substrate-limited and substrate-sufficient growth according to the initial ratio of substrate to biomass, i.e. the S0/X0 ratio. It is generally observed that the excess substrate should cause serious uncoupling between anabolism and catabolism leading to energy spilling. However, how to quantitatively describe such energy uncoupling still stays unanswered for substrate-sufficient batch culture of activated sludge. Based on the observed growth yield, a concept of energy uncoupling coefficient is postulated, from which a model is proposed to describe the dependence of the energy uncoupling degree on the S0/X0 ratio for substrate-sufficient batch culture. The energy uncoupling shows an increasing trend with the S0/X0 ratio up to its maximum. The proposed model describes both experimental and literature data satisfactorily.