GPS-X Technical Reference

99 Suspended Growth Models
Oxygen Mass Transfer Coefficient at Field Conditions Calculation
The value of the oxygen mass transfer coefficient at field conditions, K La, specifies the
*
amount of oxygen supplied to the aeration tank given the driving force C
C L
, and
the tank volume. GPS-X provides four ways for the user to specify the K La:
1. If known, the user can directly supply the K La at 20°C (no alpha, fouling, or
temperature correction) for both diffused and mechanical aeration. GPS-X
converts the K La to field conditions.
2. In the case of mechanical aerators, the user can supply an aeration power and
mechanical aerator oxygen transfer rate from which GPS-X calculates the K La.
3. In the case of diffused aeration, the user can supply an air flow rate (at either
standard or field conditions) and a standard oxygen transfer efficiency (SOTE)
from which GPS-X calculates the K La at field conditions.
Alternatively, the user can configure a DO controller which will manipulate the field K La
directly to match the desired DO concentration.The availability of these options depends on
the selected aeration method. For diffused aeration the user can enter airflow, enter K La, or
use a DO controller. For mechanical aeration the user can enter power, enter K La, or use a
DO controller. The four choices for specifying K La are discussed in more detail in the
following four sections.
Entering KLa Directly – Diffused Aeration
The K La at field conditions is calculated using Equation 6.11:
Equation 6.11
where:
K La T = mass transfer coefficient at temperature T in °C (1/day)
K La 20 = mass transfer coefficient at 20°C
θ = temperature correction factor (default value in GPS-X is 1.024)
α = wastewater correction factor for K La 20
F =diffuser fouling factor (default value in GPS-X is 1.0)
T
= wastewater temperature (°C)
GPS-X Technical Reference