GPS-X Technical Reference

Suspended Growth Models 126
ACTIVATED SLUDGE MODEL NO. 2 (ASM2)
Asm2 is no longer implemented in GPS-X, in favour of using the asm2d model (see below),
which corrects errors and deficiencies from the original published model.
ACTIVATED SLUDGE MODEL NO. 2D (ASM2D)
Introduction
This model (asm2d) is an implementation of the Activated Sludge Model No. 2d
(Henze et al., 1998). The model structure, default values and all other model aspects
follow the publication in every detail.
This model is an extension of asm1, primarily to handle biological phosphorus removal
systems. The model matrix is shown with the nomenclature used in the GPS-X
implementation. Users of this model should consult the reference (Henze et al., 1998) for
details of this model.
The asm2d model is implemented in the CNP and CNPIP library, and the Model Matrix
is found in Appendix A.
ASM2d Model Components
One major difference in the way this model is presented compared with the other models
is seen in its matrix description. The stoichiometric coefficients for ammonia and soluble
phosphorus are listed outside the table. The reason behind this is that to eliminate the
organic nitrogen state variables (xnd and snd); they are now incorporated into the other
soluble and particulate organic components as a fixed fraction. Similarly, a fixed fraction
of phosphorus is included in the organic components.
State Variables
Each of these state variables represents a spectrum of organic biodegradable material.
Another state variable is used to model the other soluble organic material, which is not
biodegradable (si). This material is part of the influent and can be produced during some
hydrolysis processes. The soluble nitrogen components consist of 1) ammonia and
ammonium (snh); and 2) nitrate and nitrite (sno). The dinitrogen gas produced (snn) is
also modelled, but is considered insoluble and immediately comes out of solution.
Oxygen (so) and inorganic soluble phosphorus (sp) are the other two soluble states. The
inorganic soluble phosphorus is typically ortho-phosphate.
GPS-X Technical Reference