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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 measurement
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 the previous page)
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. (see
Method Configuration in SOUR Setup)
Before starting a SOUR measurement remember to set the SOUR configuration from the setup menu and make
sure the instrument has been calibrated on DO.
To measure the SOUR of a sample:
• Press
and then
to select OUR measure mode.
• Press
to start taking the measurement.
• At the end of the measurement the meter will display the
computed SOUR value, the duration of the measurement and
the pressure and temperature values.
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