Using the Kinetics of Biological Flocculation and the Limiting Flux Theory for the Preliminary Design of Activated Sludge Systems. I: Model Development

Abstract

Current activated sludge models consider that the removal of biodegradable organics by suspended growth includes rapid enmeshment of the organic particles in the microbial floc, hydrolysis of the complex organic molecules into readily biodegradable organic substances, and oxidation of dissolved organic substances. All of the models assume hydrolysis is the rate-limiting step, but none consider the role that the kinetics of biological flocculation and the sludge settling characteristics may play in defining the activated sludge operating parameters. Several researchers have studied the kinetic of biological flocculation, and have analyzed its role on the removal of particulate COD in suspended growth reactors. It has been demonstrated that a large proportion of the organic matter present in sewage can be removed by biological flocculation using short hydraulic retention times and subsequent settling. This paper demonstrates that the one-dimensional limiting flux theory may be useful for coupling the sludge settling properties with the aeration tank behavior, and is a reasonable first approximation that can be used for activated sludge system design and operation.