GPS-X Technical Reference

281 Digestion Models
Combining the above equations:
Equation 10.11
The rate of biological generation of total soluble carbon dioxide (rsco2t) can be
expressed in terms of bacterial growth rates and yield coefficients. Combined with the
above equation results in the total reaction rate for dissolved CO 2 (rsco2):
Equation 10.12
where:
(yb r1)
(yd r2)
gvol
= rate of generation of sco2t by the hydrolysis of vss
= rate of generation of sco2t by the growth of methanogens
= gas constant for CO 2 in L/mole
The mass transfer of CO 2 between the liquid and gas phases (r6) is negative when CO 2 is
transferred from the liquid to the gas phase.
Ammonia
Ammonia (snh) is assumed to be produced only at the hydrolysis/acidification stage.
Ammonia (snh) is utilized by the methanogenic organisms for growth. The rate of
generation of free ammonia (rsnh) is modelled as:
Equation 10.13
where:
(yf r1)
-r2/yg
= rate of generation of ammonia by hydrolysis/acidification
= rate of consumption of ammonia due to growth of
methanogenic organisms.
The chemical equilibria and the pH calculation used for ammonia (snh) and ammonium
ion (snhi) are based on Hydromantis' pH Model..
GPS-X Technical Reference