Simultaneous storage and degradation of PHB and glycogen in activated sludge cultures

Bacteria in activated sludge are subjected to periods of substrate availability and absence of external substrates. The response of bacteria to such dynamic conditions was studied in a 2 L sequencing batch reactor (SBR) by subjecting a mixed microbial population to successive periods of external substrate availability (feast period) and no external substrate availability (famine period). In previous studies, acetate or glucose was used as single substrate leading to the storage of polyhydroxybutyrate or glycogen, respectively. In this study, a mixture of acetate and glucose was used. It appeared that both substrates were consumed simultaneously. The relative contribution of growth and storage processes was in these experiments similar as in the systems fed with a single substrate only. The ratio of substrate uptake over substrate storage was 0.6 Cmol/Cmol for both substrates. The uptake rate of acetate was not influenced by the simultaneous uptake of glucose. The degradation kinetics and rates of the storage compounds were the same as for the systems in which only one compound was stored in the activated sludge. The global performance of the culture grown on mixed substrates could therefore be described as the sum of the conversions observed in cultures fed with the individual substrates.