GPS-X Technical Reference

293 Digestion Models
AEROBIC DIGESTION MODEL
The objective of the aerobic digestion process is to stabilize and reduce the mass of solids for
disposal. In this process, microorganisms consume their own protoplasm for energy; they are
assumed to be in the endogenous phase. This phase is accounted for in the biological models
associated with the CSTR object, but in aerobic digestion, destruction of particulate inert organic
material also occurs.
The models associated with the aerobic digester are given the name dig, where
is the associated activated sludge model (such as asm1, etc.). The only difference between the
activated sludge model and its corresponding aerobic digester model is an added first-order
reaction. This additional reaction adjusts the particulate inert organic concentration to account for
the destruction of the inert organics:
Equation 10.15
where:
r xi
ki
= rate of reaction for particulate inert organics (xi) (under Parameters – Kinetics
menu of the anaerobic digester object)
= inert bioconversion rate
No loss of COD is involved in this process, and no electron acceptor is utilized. This destruction
process converts particulate inert organics (xi) to slowly biodegradable substrate (xs). The slowly
biodegradable substrate formed is then hydrolyzed, releasing an equivalent amount of readily
biodegradable COD.
GPS-X Technical Reference