The Reynolds ( Re = vL/v =Qaρ/Dn )and the (adapted) Froude number( Fr = v/√Lg = Q_a/√(D_t^5 g) )were used. The coefficients for clean water and activated sludge varied up to 66% for the same base model but show similar trends and effects for different hydrodynamic, physicochemical and geometrical parameters. The airflow rate was the main factor affecting both kLaAS and kLaCW. Next were diffusers depth and bubble size. Airflow rate and diffusers surface area had a significantly larger impact in the presence of biomass, since it promotes bubble distribution, mixing of the solution and an improved oxygen transfer, therefor demonstrating the need for an adapted model for ASPs.