Activated sludge models are used in scientific research to study biological processes in hypothetical systems.
They can also be applied on full scale wastewater treatment plants for optimisation, when carefully calibrated with reference data for sludge production and nutrients in the effluent.
[1][2] One of the main goals was to develop a model of which the complexity was as low as possible and simple to represent, though still able to accurately predict the biological processes.
An enhanced version of ASM1, simply named ASM2, was developed to include biological and chemical phosphorus removal.
As scientific understanding grew in the late 1990s, ASM2 was extended into ASM2d, principally by the addition of anoxic as well as aerobic uptake of phosphorus.