Influence of storage on kinetic selection to control aerobic filamentous bulking

Abstract

In various activated sludge systems, sludge grows under transient (unbalanced) conditions and storage of internal polymers becomes important. Differences in storage capacity under transients are often used to explain kinetic control of bulking, but storage is neither studied in detail nor usually included in modelling. For this reason, the transient response of different aerobic mixed cultures was studied by experimentally determining the role of storage. Two different mixed cultures (bulking and non-bulking) were selected in an acetate-limited medium, by continuous or intermittent feeding of a CSTR, respectively. Batch tests were used to investigate the transient response of the selected cultures as a function of the starvation time and of the ratio of the initial concentration of the substrate and sludge biomass (So/Xo). In most experimental conditions, both cultures showed that the storage of poly-hydroxybutyrate (PHB) is in general the prevailing mechanism of substrate 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 ratio So/Xo did not have a major role in determining the type and extent of the response. Starvation did not affect the response of the floc-formers to transient conditions. For the filamentous bacteria, both the growth response and, even more significantly, the storage response were negatively affected. Hence, the difference in storage capacity between filamentous and floc-forming bacteria was further increased.

Bulking sludge in biological nutrient removal systems

“…It has been shown that the configuration of the system (i.e., plug flow vs. completely mixed) has a large impact on kinetics, which will ultimately determine the size of the selector. Furthermore, storage is an intrinsic bacterial ecophysiological process that plays a key role in selector-like systems (Majone et al, 1996;Martins et al, 2003a;2003b;van Loosdrecht et al, 1997), and can influence both stoichiometry and kinetics.…”

Link between microbial composition and carbon substrate-uptake preferences in a PHA-storing community

“…Enhanced PHA storage was found in activated sludge systems subjected to alternate carbon substrate availability, also designated as feast and famine (FF) (Majone et al, 1996;van Loosdrecht et al, 1997). Under FF, microorganisms that can rapidly store the substrate have a competitive advantage.…”

Experimental evaluation of starch utilization mechanism by activated sludge

“…Consequently, there is less emphasis on the extracellular hydrolysis of complex organic matter because a significant part of the ''slow oxygen uptake rate'' is due to growth on stored substrate (Gujer et al, 2000), whereas in ASM1, this is solely due to growth on hydrolyzed substrate. Experiments indicate, however that the extent of storage and the level of internal hydrolysis depend much on the parameters of system operation and feast (presence of external substrate) and famine (absence of external substrate) conditions created within the system (Majone et al, 1996). Recent modeling efforts attempt to bring clarification to simultaneous substrate storage and growth (Beun et al, 2000;Karahan-Gül et al, 2003;Krishna and van Loosdrecht, 1999).…”