Reduced Growth Yield of Activated Sludge in Organic Protonophore-Containing Batch Culture

The effects of organic protonophores 2,4-dinitrophenol (dNP) and para-nitrophenol (pNP) on the observed growth yield (Y(obs)) was studied using batch cultures of activated sludge microorganisms. A growth yield model was proposed in relation to the ratio of initial protonophore concentration (C(u)) to initial biomass concentration (X(0)) and was verified with experimental data. It was found that Y(obs) decreased with the increase of the C(u)/X(0) ratio, while the specific rate of glucose consumption was increased. Results showed that the C(u)/X(0) ratio could more reasonably reflect the real strength of organic protonophore exerted to activated sludge than using C(u) only. Based on the concept of growth yield, a model describing the uncoupling degree between energy generated via electron transport system and energy used for growth was further developed for protonophore-containing batch culture. It was shown that more than 60% of glucose was consumed through a futile cycle of energy rather than for growth at higher C(u)/X(0) ratios. This research usefully shows that the dissipation of energy via uncoupling biochemical processes can reduce excessive production of activated sludge markedly.