E 5: Dissolved Oxygen in Water

BOD device• This device is used to measure the dissolved oxygen (DO) in the 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 anaerobicdecomposition of organic material in water.•A picture of a compost yard.•This is where 34 percent of all aerobic decomposition occurs.

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