GPS-X Technical Reference

151 Suspended Growth Models
The stoichiometric parameters specified in the “hydrolysis”, “acidogens” and
“methanogens” sections are the following yield coefficients:
Y e: Yield for hydrolytic enzymes on insoluble or soluble substrate (C e/C ss).
Y a: yield for acidogens on monomers species (C xa/C mo).
Y m: Yield for methanogens on volatile fatty acids (C xm/S lf).
Kinetic Parameters
The model kinetic parameters are:
k his: hydrolysis rate constant for insoluble substrate (g COD/m 3 .d).
k hs: hydrolysis rate constant for soluble substrate (g COD/m 3 .d).
k amm: ammonification rate constant for organic nitrogen contained in proteins
(g N/m 3 .d).
k mo: maximum specific consumption rate of monomers by acidogenic biomass (g
COD/m 3 .d).
Process Rates
k ac: maximum specific consumption rate of volatile fatty acids by methanogenic
biomass (g COD/m 3 .d).
d a: decay rate constant of acidogens (g COD/m 3 .d).
d m: decay rate constant of methanogens (g COD/m 3 .d).
d e : deactivation rate constant of hydrolytic enzymes (g COD/m 3 .d).
The process rates described in the model are:
Hydrolysis of insoluble substrate
Equation 6.35
The hydrolysis rate of insoluble substrate is considered to be first order with respect to
the concentration of insoluble substrate and to the concentration of hydrolytic enzymes,
and to be inversely proportional to the concentration of acidogenic biomass, due to a
limited surface area available which could cause mass transfer limitations.
GPS-X Technical Reference