22
The Specific Oxygen Uptake Rate (SOUR), also known as the oxygen consumption or respiration rate,
is defined as the milligram of oxygen consumed per gram of volatile suspended solids (VSS) per
hour. This quick test has many advantages: rapid measure of influent organic load and biodegradability,
indication of the presence of toxic or inhibitory wastes, degree of stability and condition of a sample,
and calculation of oxygen demand rates at various points in the aeration basin.
The following equation is used for SOUR determination:
SOUR = OUR / Solids Weight
where:
OUR
is the Oxygen Uptake Rate (see equation on page 20)
Solids Weight
is the
Total solids
or the
Volatile suspended solids
weight in g/L
Temperature correction:
The SOUR value is corrected to 20 °C (68 °F) according to the Farrel and Bhide equation:
SOUR
20
=SOUR
T
x
Θ
(20-T)
Where T is the measured temperature in °C and
Θ
is a temperature dependent variable:
Θ
= 1.05 for T above 20 °C
Θ
= 1.07 for T below 20 °C
This calculation is valid only for temperature values in the range 10 to 30 °C. Temperature correction is
performed only if the option
SOUR @ 20 °C
is enabled from
SOUR configuration
in the setup menu.
Before starting a SOUR test remember to set the SOUR configuration from the setup menu.
SOUR measurement screen:
SOUR MEASUREMENT
If the SOUR value is corrected to 20 °C (68 °F) the message “
@20°C
”, or ”
@68
°
F
” according to
the currently selected temperature unit, will be displayed above the measured temperature.
Press
Start
to begin a new SOUR test.
If the DO value is less than the minimum start DO value, the meter will display an error message,
and the test cannot be started.
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