GPS-X Technical Reference

125 Suspended Growth Models
The organic material is categorized according to a number of characteristics. First, is the
biodegradability of the material. The non-biodegradable organics pass through the system
unchanged and can be further categorized according to their physical state (soluble or
particulate), which is removed from the system by different pathways. The particulate
material is generally removed with the waste activated sludge, while the soluble material
leaves with the effluent. The biodegradable material is categorized as either readily or
slowly biodegradable. The Task Group treated the former as soluble material, while the
latter was treated as particulate material (this is not strictly correct, but simplifies
matters). The readily biodegradable organics may be utilized for cell maintenance or
growth with a transfer of electrons to the acceptors. The particulate (slowly)
biodegradable substrate is hydrolyzed to readily biodegradable material, assuming no
energy utilization and no corresponding use of electron acceptor.
The hydrolysis rate is usually slower than the utilization of readily biodegradable
substrate so that it is the rate limiting step, if only slowly biodegradable substrate is
available.
Two types of biomass are modelled:
1. heterotrophic; and
2. autotrophic
The heterotrophic biomass is generated by the growth on readily biodegradable substrate
under aerobic or anoxic conditions and decays (including endogenous respiration, death,
predation and lysis) under all conditions. The autotrophic biomass is generated under
aerobic conditions only utilizing ammonia for energy and decays under all conditions.
The nitrogenous material is categorized according to its biodegradability and physical
state. The non-biodegradable particulate material is modelled as a fraction of the nonbiodegradable
particulate COD, while the non-biodegradable soluble material is ignored.
The biodegradable nitrogenous material is divided into ammonia (free and ionized),
soluble organic and particulate organic. Particulate organic is hydrolyzed to soluble
organic, while soluble organic is converted to ammonia by the heterotrophic biomass.
The conversion of ammonia to nitrate by the autotrophs is assumed to take place in one
step.
The Model Matrix for asm1 is found in Appendix A.
GPS-X Technical Reference