Download E 5: Dissolved Oxygen in Water

E 5: Dissolved Oxygen in Water
E1: Outline biochemical oxygen
demand (BOD)
• Biochemical oxygen demand, also known as
BOD is The amount of oxygen consumed by
these organisms in breaking down the waste.
• The oxygen is measured in its dissolved form
as called dissolved oxygen (DO). As more
oxygen (02) is consumed than is produced, the
dissolved oxygen levels begin to decline and
some sensitive animals may migration,
weaken, or die.
BOD Factors:
• DO levels fluctuate seasonally and over a 24-hour
period.
• Factors include:
• water temperature
– Cold water holds more oxygen than warm water
– Thermal discharges, such as water used to cool
machinery in a manufacturing plant or a power
plant, raise the temperature of water and lower
its oxygen content
• altitude
• At higher altitudes water holds less oxygen
Effects of vary amounts of BOD
• Aquatic animals are greatly influenced by
lowered DO levels in the early morning on hot
summer days when stream flows are low,
water temperatures are high
• Aquatic plants are affected as they go through
a series of cycles and have not been producing
oxygen since sunset.
E2: Distinguish between aerobic and anaerobic
decomposition of organic material in water.
Anaerobic Decomposition
• ANAEROBIC (without oxygen) decomposition.
• Anaerobic decomposition takes place in nature.
• The decomposition of the organic mud at the bottom
of marshes and in buried organic materials where O2
does not have access.
• Intensive reduction of organic matter by putrefaction is
usually accompanied by disagreeable odors of
hydrogen sulfide and reduced organic compounds
which contain sulfur, such as mercaptans.
• Relatively active in low levels of BOD levels.
• Organic compounds break down by the action of
living organisms that do not require air in the
normal sense.
• These organisms use nitrogen, phosphorus, and
other nutrients to live, they reduce the organic
nitrogen to organic acids and ammonia.
• The carbon from the organic compounds which is
not utilized in the cell protein is reduced to the
form of methane (CH4).
• A small portion of carbon may be respired as
carbon dioxide (C02).
Aerobic Decomposition
• AEROBIC (with oxygen) decomposition and
stabilization.
• The aerobic process is most common in nature
• In aerobic decomposition, living organisms, which use
oxygen, feed upon the organic matter. They use the
nitrogen, phosphorus, some of the carbon, and other
required nutrients.
• Much of the carbon serves as a source of energy for
the organisms and is burned up and respired as carbon
dioxide (C02). Since carbon serves both as a source of
energy and as an element in the cell protoplasm, much
more carbon than nitrogen is needed. Generally about
two-thirds of carbon is respired as C02, while the other
third is combined with nitrogen in the living cells.
E3:Describe the process of
eutrophication and its effects.
• Eutrophication is when the ecosystem
responses to human activities that fertilize
water bodies with nitrogen (N) and
phosphorus (P).
• And often leads to changes in animal and
plant populations and degradation of water
and habitat quality.
• Low dissolved oxygen (DO) in the water is a
common consequence.
E4: Describe the source and effects of
thermal pollution in water.
• Main Sources:
• The waste heat from electrical generating
stations (transferring the cooling water obtained
from local water bodies such as a river, lake, or
ocean.)
• steam engines
• internal combustion engines
• Effects:
• Thermal shock to the environment.
– water can absorb thermal energy with only small
changes in temperature, most aquatic organisms
have developed enzyme systems that operate in
only narrow ranges of temperature
• Changes in the levels dissolved oxygen (DO)
• The redistribution of organisms in the local
community.
– periodic heat treatments used to keep the cooling
system clear of fouling organisms that clog the
intake pipes can cause fish mortality