The Activated Sludge SIMulation program ASIM is introduced as a didactic tool to be used in design courses for the simulation of the dynamic behaviour of modern nutrient removal activated sludge systems. It allows for free definition of the biokinetic model, the flow scheme, process control strategies and load variation. Its user interface is simple enough to be used in the classroom but powerful enough to support even professional work.

The most difficult aspect of ASIM is the preparation of the biokinetic model (transformation processes) to be used. A systematic use of stoichiometric conservation principles simplifies this task and at the same time reduces the number of empirical parameters. The practical application of conservation principles for charge, elements and theoretical COD is presented in detail. Composition equations are introduced as a link to the wastewater treatment plant reality.