GPS-X Technical Reference

287 Digestion Models
The rest of the dissociation constants are not corrected for temperature changes in the
basic model.
Gas transfer parameters are also defined on this form. The mass transfer coefficient for
carbon dioxide gas (sco2) between the liquid and gas phases (KLaco2) is not corrected by
temperature in the basic model. Henry's law constant for carbon dioxide (henryco2) is
also included in this item and is not corrected for temperature.
Anaerobic Digestion Model #1 (ADM1)
Anaerobic Digestion Model #1 (ADM1) (Batstone et al., 2002) is implemented in GPS-X
according to the ADM1 COST Benchmark (Rosen and Jeppsson, 2002), with the
following changes:
Several differential equations that describe the acid-base equilibrium of the
system (equations for S va-, S bu-, S pro-, S ac-, S hco3-, and S nh3) have been converted to
algebraic equations as described in Table B.3 of Batstone et al. (2002). These
processes are very fast and contribute to the stiffness of the system of differential
equations.
The differential equation for S h2 has been converted to an algebraic equation to
improve the simulation speed. This process is very fast and contributes to the
stiffness of the system of differential equations. This approach is described by
Rosen et al. (2005).
These changes substantially increase the solution speed of ADM1 in GPS-X and allow an
integration algorithm other than Gear’s Stiff to be used. Double Precision arithmetic
should be used when solving ADM1 in GPS-X
(accessed in Options > Preferences > Build tab)
The structured model includes five process steps including disintegration, hydrolysis,
acidogenesis, acetogenesis and methanogenesis. The model uses 32 dynamic state
variables, 6 acid-base kinetic processes, 19 biochemical processes, and 3 gas-liquid
transfer processes.
A simplified ADM1 material flow diagram is shown in Figure 10-11. For a full
description of the model, the reader is referred to Batstone et al,. (2002). Implementation
details are found in Rosen and Jeppsson (2002).
GPS-X Technical Reference