6
2.
The Method
2.1 Biochemical Oxygen Demand (BOD)
The biochemical oxygen demand (BOD) of waste water, industrial effluents and surface
water is an expression for the amount of oxygen consumed by the decomposition of
organic matter in a biochemical process.
2.2 Principle of Measurement
The BOD system, consisting of the sample bottle and the BOD sensor, represents a
closed system. In the bottle, above the sample itself, is a defined volume of air. During
the BOD measurement, the bacteria in the sample consume the dissolved oxygen in
the sample. This is replaced by oxygen in the bottle above the sample. The carbon
dioxide released at the same time react with the potassium hydroxide in the seal gasket.
This generates a decrease in pressure within the system. This is measured by the BOD
sensor and displayed as a BOD value in mg/l O
2
.
2.3 Preparing the Sample / Brief Summary
•
Estimate the measurement range and select the volume for the sample (4.1).
•
Carry out necessary pre-treatment of the sample (e.g., setting the pH value; filtering; etc.) (4.2).
•
Measure the volume of the sample precisely, using the overflow measurement flask
and transfer it to the BOD bottle, with the aid of a funnel. If necessary, add nitrification
inhibitor (4.1).
•
Insert the magnetic stirring rod.
•
Place 3-4 drops of KOH solution into the seal gasket. Then insert the gasket in the
neck of the bottle.
•
Screw the BOD sensors to the sample bottles.
•
Place the bottle in the bottle rack.
•
Start the measurement (3.10).
•
Incubate the sample in accordance with the instructions (e.g. BOD
5
for 5 days at 20 °C)
Содержание OxiDirect BOD-System
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