Sludge Age, Stability, and Safety Factor for the Biofilm-Activated Sludge Process Reactor

The average sludge age (theta(c)) of the activated sludge process (ASP)-biofilm were developed and verified experimentally. In addition, the stability and safety factor were investigated against theta(c) through a series of curves. These curves are important to explain, in concept, the function of the hybrid system under different values of theta(c). The proposed curves of this study are simple and can be modified for any specified wastewater. The definition of theta(c) of ASP was found to be applicable to the hybrid system after including the biofilm. A ratio ranging from 70 to 80% of the total mass of biofilm may be used in the definition of theta(c) to give close results with the experimental values. Furthermore, the minimum sludge age (theta(M)(c)) does not exist in the hybrid reactor because of the presence of biofilm; however, theta(c) should come down to a critical value under some specific conditions of the reactor. Water Environ. Res., 84, 506 (2012).