DO
About Dissolved Oxygen
Measurement
page | 57
away from the polarizable electrode is linearly proportionate to the
amount of oxygen available in the electrolyte, hence this movement
of electrons is representative of the amount of dissolved oxygen left in
the electrolyte.
The advantage of a polarographic cell is that the cathode remains intact.
The current fl ow of the polarographic cell is also linearly proportional
to the amount of oxygen present in the electrolyte, enabling the cell to
provide highly accurate measurements at low oxygen levels.
Polarographic self-stirring DO/BOD probes are available
f
or use with the Eutech CyberScan research-grade bench
meters DO 6000 and PCD 6500 in US EPA-approved auto
ve-day BOD testings.
BOD & COD
The BOD test measures the molecular oxygen utilized in the
biodegradation of organic material and the oxidation of inorganic
material. By measuring the amount of oxygen dissolved in samples at
the beginning and end of a specifi ed incubation period, the relative
oxygen requirements of wastewaters, effl uents, and polluted waters
can be determined.
BOD
t
(mg/L) =
D
1
- D
2
P
BOD
t
= Oxygen uptake during incubation period t
D
1
= DO of diluted sample immediately after preparation (mg/L)
D
2
= DO of diluted sample after incubation period t (mg/L)
P = Decimal volumetric fraction of sample used
BOD is similar to the Chemical Oxygen Demand (COD), which
also measures relative oxygen-depletion. However, the possible
presence of non-biologically oxidisable may render the COD test to
be less accurate.
The COD Test is often used to measure the amount of organic compounds
in surface water by measuring the amount of oxygen required to oxidize
an organic compound to carbon dioxide, ammonia and water. The basis
of the COD test is that anything can be oxidized into carbon dioxide using
a strong oxidizing agent in acidic environments. A blank sample, created
by adding all reagents to distilled water is usually used as a control in
COD measurements.
Both the BOD and COD tests are means to measure the relative
oxygen-depletion eff ect of a waste contaminant, and are widely used
to monitor pollution levels. The BOD test measures the oxygen demand
of biodegradable pollutants whereas the COD test measures the
oxygen demand of biogradable pollutants plus the oxygen demand of
non-biodegradable oxidizable pollutants.
However, because COD measures everything that can be chemically
oxidised and not just the level of biologically active organic matter, the
possibility of non-biological oxidizable may render the COD Test as a less
accurate method compared to the BOD method.
<< Shrimp Farming
>> Water Treatment
(28 stránky)
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Komentáře k této Příručce