title: Rethinking growth and decay kinetics in activated sludge - towards a new adaptive kinetics approach.
abstract: Growth kinetics in activated sludge modelling (ASM) are typically assumed to be the result of intrinsic growth and decay properties and thus process parameters are deemed to be constant. The activity change in a microbial population is expressed in terms of variance of the active biomass fraction and not actual shifts in bacterial cellular activities. This approach is limited, in that it does not recognise the reality that active biomass is highly physiologically adaptive. Here, a strong correlation between maximum specific growth rate (μmax) and decay rate (be) of ordinary heterotrophic organisms was revealed in both low solids retention times (SRT) and high SRT activated sludge systems. This relationship is indicative of physiological adaptation either for growth (high μmaxand be) or survival optimization (low μmaxand be). Further, the nitrifier decay process was investigated using molecular techniques to measure decay rates of ammonia oxidizing bacteria and nitrite oxidizing bacteria over a range of temperatures. This approach revealed decay rates 10-12% lower than values previously accepted and used in ASM. These findings highlight potential benefits of incorporating physiological adaptation of heterotrophic and nitrifying populations in future ASM.
authors.affiliation: Ingenieurbüro Friedrich, August-Bebel-Strasse 14, 19055 Schwerin, Germany E-mail: friedrich@ibf-thiox.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Friedrich
authors.affiliation: Brown and Caldwell, 2301 Lucien Way, Suite 250, Maitland, FL, USA.
authors.forename: Jose
authors.initials: J
authors.lastname: Jimenez
authors.affiliation: Department of Civil & Environmental Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Pruden
authors.affiliation: Department of Civil & Environmental Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Jennifer H
authors.initials: JH
authors.lastname: Miller
authors.affiliation: Department of Civil & Environmental Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Jacob
authors.initials: J
authors.lastname: Metch
authors.affiliation: Dynamita, 7 Eoupe, 26110 Nyons, France.
authors.forename: Imre
authors.initials: I
authors.lastname: Takács
mesh_terms: D000222:Adaptation, Physiological; D020562:Betaproteobacteria / Q000254:growth & development*; D018533:Biomass; D019149:Bioreactors / Q000382:microbiology*; D052836:Heterotrophic Processes; D007700:Kinetics; D008954:Models, Biological; D058465:Nitrification; D012722:Sewage / Q000382:microbiology*; D018508:Water Purification / Q000379:methods
chemical_list: D012722:Sewage