Nova-Tech 2700 Series Benchtop Meters User Manual
Page 45
41
Applications
Oxygen is essential for fish, invertebrate, plant, and aerobic bacteria respiration.
DO levels below 3 ppm are stressful to most aquatic organisms. Levels below 2
or 1 ppm will not support fish. Fish growth and activity usually require 5 to 6 ppm
of DO, an important consideration for Aqua-culture industry.
Low DO indicates a demand on the oxygen of the system. Natural organic
material such as leaves accumulate in the stream and create an oxygen demand
as it is decomposed. Organic materials from human activities also create an
oxygen demand in the system. Micro-organisms consume oxygen as they
decompose sewage, urban and agricultural run-off, and discharge from food-
processing plants, meat-packing plants and diaries. There is an optimum DO
level for this process and if the DO level falls too low, the micro-organisms die
and the decomposition ceases. When DO level is too high, this indicates too
much power is used than necessary for aeration resulting in an inefficient
process.
In boiler water application, presence of oxygen in the water will increase corrosion
and helps build up boiler scale that inhibits heat transfer. In such instance it is
critical to keep DO concentration to a minimum.
Some pollutants such as acid mine drainage produce direct chemical demands
on oxygen in the water. DO is consumed in the oxidation-reduction reactions of
introduced chemical compounds such as nitrate (NO
3
1-
) and ammonia (NH
4
1+
),
sulfate (SO
4
2-
), and sulfite (SO
3
2-
) and ferrous (Fe
2
+
) and ferric (Fe
3
+
) ions.
These are important consideration for water and wastewater treatment industry.