Studies on the response of activated sludge to shock–loadings

The response of heterogeneous populations to shockloading was studied under a variety of operational conditions using synthetic wastes consisting of glycerol, glucose, and a mixture of glucose and glycerol. In all experiments, the cells were acclimated to glycerol. The addition of glucose as a shockloading at various times during the aeration period caused an immediate cessation of glycerol metabolism, and glycerol was not again actively metabolized until all glucose had been assimilated. Experiments conducted at various initial sludge concentrations showed that this effect was not dependent upon biological solids level. Glycerol metabolism was also blocked when glucose was applied as a shockloading to a system operating under severe nitrogen deficiency, further reenforcing the conclusion that there is a blockage mechanism for catabolic pathways which operates to suppress enzyme function rather than enzyme synthesis. It was also found that considerable amounts of metabolic intermediates or end products were released during glucose metabolism regardless of the presence or absence of glycerol. In systems containing a source of nitrogen, these products were metabolized after dissimilation of glucose. In resting cell suspensions, the metabolic intermediates were not subsequently removed, indicating that their metabolism depended upon the synthesis of new enzymes. Using old cell sludge, concurrent rather than sequential removal of glycerol and glucose was observed. The results using two component (C 6 C 3 ) carbon sources were in general the same as for C 6 C 6 synthetic wastes. The results provide further evidence for the generality of sequential substrate removal, and suggest that the metabolite suppressing catabolism of glycerol lies below the triose level.