INFLUENCE OF STORAGE ON KINETIC SELECTION TO CONTROL AEROBIC FILAMENTOUS BULKING

In various activated sludge systems, sludge grows under transient (unb alanced) conditions and storage of internal polymers becomes important . Differences in storage capacity under transients are often used to e xplain kinetic control of bulking, but storage is neither studied in d etail nor usually included in modelling. For this reason, the transien t response of different aerobic mixed cultures was studied by experime ntally determining the role of storage. Two different mixed cultures ( bulking and non-bulking) were selected in an acetate-limited medium, b y continuous or intermittent feeding of a CSTR, respectively. Batch te sts were used to investigate the transient response of the selected cu ltures as a function of the starvation time and of the ratio of the in itial concentration of the substrate and sludge biomass (So/Xo). In mo st experimental conditions, both cultures showed that the storage of p oly-hydroxybutyrate (PHB) is in general the prevailing mechanism of su bstrate removal. In particular, the culture dominated by floc-formers showed very fast response to the substrate spike with a high observed yield. Storage was practically the only metabolism occurring. The rati o So/Xo did not have a major role in determining the type and extent o f the response. Starvation did not affect the response of the floc-for mers to transient conditions. For the filamentous bacteria, both the g rowth response and, even more significantly, the storage response were negatively affected. Hence, the difference in storage capacity betwee n filamentous and floc-forming bacteria was further increased. Copyrig ht (C) 1996 IAWQ.