GPS-X Technical Reference

Suspended Growth Models 192
Modelling of Gas Transfer in Open Basin HPO
The gas transfer to the bulk liquid phase of a biological reactor is modelled using a
dynamic mass balance written for each dissolved gas (Hydromantis, 2011). For
example, a dissolved oxygen mass balance around a completely stirred tank reactor
(CSTR) is shown below.
Equation 6.57
where:
V
CL
Q
C in
K La
C * ∞
r
= reactor volume (m3)
= concentration of dissolved oxygen (DO) in the reactor (mg/L)
= influent flow rate (m3/d)
= concentration of DO entering reactor (mg/L)
= oxygen mass transfer coefficient at field conditions (1/day)
= DO saturation concentration at field conditions (mg/L)
= rate of use of DO by biomass (g/day), the respiration rate
The volume, flows, and reaction rates are known from specifications or other modelling
equations, leaving two terms that must be calculated in order to solve the dissolved
oxygen mass balance over time for the DO concentration in the reactor, CL:
1. DO saturation concentration at field conditions, C * ∞, and
2. Oxygen mass transfer coefficient at field conditions, K La
GPS-X Technical Reference