Reaction rate constants and mean population percentage for nitrifiers in an alternating oxidation ditch system

This paper presents a methodology for the determination of reaction rate constants for nitrifying bacteria and their mean population percentage in biomass in an alternating oxidation ditch system. The method used is based on the growth rate equations of the ASM1 model (IWA) (Henze et al. in Activated sludge models ASM1, ASM2, ASM2d, and ASM3. IWA Scientific and Technical Report no. 9, IWA Publishing, London, UK, 2000) and the application of mass balance equations for nitrifiers and ammonium nitrogen in an operational cycle of the ditch system. The system consists of two ditches operating in four phases. Data from a large-scale oxidation ditch pilot plant with a total volume of 120 m³ within an experimental period of 8 months was used. Maximum specific growth rate for autotrophs (μ _A) and the half-saturation constant for ammonium nitrogen (K _NH) were found to be 0.36 day⁻¹ and 0.65 mgNH₄–N/l, respectively. Additionally, the average population percentage of the nitrifiers in the biomass was estimated to be around 3%.