PASCO PS-2108 Dissolved Oxygen Sensor - Manual (Page 26)

PASPort Dissolved Oxygen Sensor Model No. PS-2108
22 ®
Experiment 4: Biochemical Oxygen Demand
1
Background
Biochemical oxygen demand (BOD) is an important measure of water quality. BOD is a
measurement of the quantity of oxygen used by microorganisms in the aerobic oxidation of
organic matter. In rivers and streams with high BOD levels, much of the available dissolved
oxygen is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they
need to live. This is a condition that may be exacerbated by excessive nitrogenous wastes in
runoff water.
Procedure
1. Measure the dissolved O
2
concentration and water temperature in a waterway, preferably on
site using the PASPort logger of choice, with the dissolved oxygen sensor.
2. Collect a sample of the water in an airtight, black bottle, and incubate the water sample at
room temperature for 5 days.
3. Bring the water sample to approximately the same temperature as the first sample and
measure the dissolved O
2
concentration.
4. Calculate the BOD level: mg/l dissolved O
2
(original sample) - mg/l dissolved O
2
(5-day
old sample).
5. Score the BOD as follows:
4 (excellent): less than 2 mg/l
3 (good): 2- 4mg/l
2 (fair): 4.1-10 mg/l
1 (poor): greater than 10 mg/l
1.Adapted from a 1996 publication by Stevens Institute of Technology