Modeling and simulation of activated sludge process with cyclic feeding for treatment of highly loaded wastewater

The treatment of strongly loaded wastewater (COD > 1,5 kg m(-3) by an activ ated sludge process (aeration basin + clarifier) depends both on the abilit y of the activated sludge to remove the soluble organic pollution and on th e efficiency of the separation of the treated water from the biomass. The s eparation ability of the activated sludge notably depends on the hydraulic configuration of the aeration basin: biomass settleability can be controlle d by completely mixed reactors (CMR) in series, plug-flow reactors or inter mittently fed systems. Moreover, the biomass settleability is linked to the extracellular polymers which are largely composed of microbial exopolysacc harides (EPS). A low level of EPSs indicates a sludge deflocculation proble m, whereas a high level of EPSs means that sludge settleability could be hi ndered because of an excessive growth of filamentous organisms. Experiments show that the use of only one CMR, fed in a cyclic way with permanent oxyg enation and return sludge flow leads to good settleability and effluent qua lity. The purpose of this paper is to propose a very simple model, based on experiments, in order to optimize the cyclic feeding period by simulations .