10.2190/2X4N-UGMW-4M4P-TCH2 2X4NUGMW4M4PTCH2 1 System Dynamics Modeling of Biological Reactors For Waste Water Treatment 213 240 20020509 20020509 20020509 20020509 2X4NUGMW4M4PTCH2.pdf http://baywood.metapress.com/link.asp?target=contribution&id=2X4NUGMW4M4PTCH2 3 Bhakta Kabi Das Manas Bandyopadhyay Pratap K. J. Mohapatra Indian Institute of Technology, Kharagpur, India This article presents a system dynamics model of an activated sludge plant that is used to treat waste water biologically under aerobic conditions. Three different physical flows (flow of liquid, biomass, and substrate) are considered in the model. the model is simulated with the help of IGRASP (software package). the transient and steady state behavior of the growth of biomass, sludge production, the treatment efficiency, and their sensitivity to parameter variations are studied in detail. Policies for recirculation of activated biomass in the treatment plant are evaluated. 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