Organic matter
Biochemical oxygen demand, BOD (BODs)
BODs means a 5-day biochemical oxygen demand. The BOD analysis was developed in Britain shortly before the tum of the century The idea of the analysis was
that in polluted water there is an oxygen demand caused by micro-organisms. The
required oxygen demand was used to measure the extent of the pollution. As the
oxygen demand increases by increasing temperatures and time of reaction- see Fig
2.3- it was originally decided to use the standard values 65° F (approx. l8°C) and 5
days. Now the temperature is standardized at 20°C.
The BOD-analysis is used to measure the oxygen demand of the micro-organisms
for oxidation of organic matter and ammonia. In the course of 5 days, the· major part
of the biodegradable matter will be oxidized which corresponds to the horizontal
level of the 20 degree curve in Fig 2.3.
As the oxygen demand is normally only measured after 5 days, no information is
available about the form of the curve as shown in Fig 2.3. The f?rm of the curve may
vary considerably as shown in Fig 2.4. The analysis does not reveal the amount of
degradable organic matter and ammonia oxidized.
Different organics have different oxygen demands per gramme of matter and this
means that the BOD-analysis only gives an approximate estimate of the weight of
oxidized organic matter.
The measurement of the BOD is carried out as shown in Fig 2.5. The classical
dilution method is most frequently used /11/. Polluted water is mixed with clean
aerated water. The mixture is poured into a bottle which is sealed so that there is no
air above the liquid. The micro-organisms in the polluted water consume oxygen,
and it is necessary to ensure that oxygen is present for the process ailS days. If the
oxygen is depleted, or if its concentration becomes low, the measuring result cannot
be used. It is therefore necessary to make dilution series so that at least one bottle is
obtained in which the oxygen content is still sufficiently high after 5 days.
g O,tm•
~-·-- 30"C
~--=-. --=-· __;;• 20. c
100
5
10
15
20
25
30 days
Fig2.3
Typical BOD-curves. From /9/.
40
Biochemical oxygen demand, BOD (BODs)
BODs means a 5-day biochemical oxygen demand. The BOD analysis was developed in Britain shortly before the tum of the century The idea of the analysis was
that in polluted water there is an oxygen demand caused by micro-organisms. The
required oxygen demand was used to measure the extent of the pollution. As the
oxygen demand increases by increasing temperatures and time of reaction- see Fig
2.3- it was originally decided to use the standard values 65° F (approx. l8°C) and 5
days. Now the temperature is standardized at 20°C.
The BOD-analysis is used to measure the oxygen demand of the micro-organisms
for oxidation of organic matter and ammonia. In the course of 5 days, the· major part
of the biodegradable matter will be oxidized which corresponds to the horizontal
level of the 20 degree curve in Fig 2.3.
As the oxygen demand is normally only measured after 5 days, no information is
available about the form of the curve as shown in Fig 2.3. The f?rm of the curve may
vary considerably as shown in Fig 2.4. The analysis does not reveal the amount of
degradable organic matter and ammonia oxidized.
Different organics have different oxygen demands per gramme of matter and this
means that the BOD-analysis only gives an approximate estimate of the weight of
oxidized organic matter.
The measurement of the BOD is carried out as shown in Fig 2.5. The classical
dilution method is most frequently used /11/. Polluted water is mixed with clean
aerated water. The mixture is poured into a bottle which is sealed so that there is no
air above the liquid. The micro-organisms in the polluted water consume oxygen,
and it is necessary to ensure that oxygen is present for the process ailS days. If the
oxygen is depleted, or if its concentration becomes low, the measuring result cannot
be used. It is therefore necessary to make dilution series so that at least one bottle is
obtained in which the oxygen content is still sufficiently high after 5 days.
g O,tm•
~-·-- 30"C
~--=-. --=-· __;;• 20. c
100
5
10
15
20
25
30 days
Fig2.3
Typical BOD-curves. From /9/.
40