Physiological adaptation of growth kinetics in activated sludge

• Published in: Water research (Oxford) 2015-11, Vol.85, p.22-30
• Main Authors: Friedrich, M., Takács, I., Tränckner, J.
• Format: Article
• Language: English
• Subjects: Activated sludge; Adaptation; Adaptation, Physiological; Bacteria; Bacteria - growth & development; Bacterial Physiological Phenomena; Decay; Decay rate; Growth; Kinetics; Mathematical models; Optimization; OUR; Physiological adaptation; Respiration; Sewage - microbiology; Sludge; Waste Disposal, Fluid - methods
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2015.08.010

Physiological adaptation as it occurs in bacterial cells at variable environmental conditions influences characteristic properties of growth kinetics significantly. However, physiological adaptation to growth related parameters in activated sludge modelling is not yet recognised. Consequently these parameters are regarded to be constant. To investigate physiological adaptation in activated sludge the endogenous respiration in an aerobic degradation batch experiment and simultaneous to that the maximum possible respiration in an aerobic growth batch experiment was measured. The activated sludge samples were taken from full scale wastewater treatment plants with different sludge retention times (SRTs). It could be shown that the low SRT sludge adapts by growth optimisation (high maximum growth rate and high decay rate) to its particular environment where a high SRT sludge adapts by survival optimization (low maximum growth rate and low decay rate). Thereby, both the maximum specific growth rate and the decay rate vary in the same pattern and are strongly correlated to each other. To describe the physiological state of mixed cultures like activated sludge quantitatively a physiological state factor (PSF) is proposed as the ratio of the maximum specific growth rate and the decay rate. The PSF can be expressed as an exponential function with respect to the SRT. [Display omitted] •μmax can be expressed in terms of OURmax/OURe.•Maximum respiration rate decreases faster in low SRT sludge than in high SRT sludge.•Maximum specific growth rate and decay rate were strongly correlated to each other.•Physiologically low SRT sludge is growth optimised and high SRT sludge is survival optimised.•Physiological state factor was defined as ratio of maximum specific growth rate and decay rate.