Question

What are the effects of increasing organic waste on dissolved oxygen content and biochemical oxygen demand of water?

Answer 1

The stream system both produces and consumes oxygen. It gains oxygen from the atmosphere and from plants as a result of photosynthesis. Running water, because of its churning, dissolves more oxygen than still water, such as that in a reservoir behind a dam. Respiration by aquatic animals, decomposition, and various chemical reactions consume oxygen.

Wastewater from sewage treatment plants often contains organic materials that are decomposed by microorganisms, which use oxygen in the process. (The amount of oxygen consumed by these organisms in breaking down the waste is known as the biochemical oxygen demand or BOD. A discussion of BOD and how to monitor it is included at the end of this section.) Other sources of oxygen-consuming waste include stormwater runoff from farmland or urban streets, feedlots, and failing septic systems.

Oxygen is measured in its dissolved form as dissolved oxygen (DO). If more oxygen is consumed than is produced, dissolved oxygen levels decline and some sensitive animals may move away, weaken, or die.

DO levels fluctuate seasonally and over a 24-hour period. They vary with water temperature and altitude. Cold water holds more oxygen than warm water (Table 5.3) and water holds less oxygen at higher altitudes. 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. Aquatic animals are most vulnerable to lowered DO levels in the early morning on hot summer days when stream flows are low, water temperatures are high, and aquatic plants have not been producing oxygen since sunset.

Answer 2

Effects of increasing organic waste on DO and BOD  of water

Explanation:

• There are good amount of living organisms in all fresh water bodies and it requires oxygen to breath and survive.
• The oxygen is found in dissolved form in water and it varies from 5 mg/l to 7 mg/l depends on the water quality.
• Higher the dissolved Oxygen (DO) in water is always the better for living organisms. Let us see what happens when wastewater containing high BOD enters into a good water body. The reason for high BOD in wastewater is due to the presence of dissolved organic solids.
• The wastewater with high organic solids enter in a fresh water body, the microorganisms (primary consumers) present in pure water will try to consume it as its primary food source.
• If the dissolved organic solids are minimal they degrade it and convert into simple molecules with the help of dissolved oxygen present in water.
• If the Organic contents are much higher (known as high BOD) in wastewater the bacteria try to degrade it completely and they consume all dissolved oxygen for this process.
• Once the DO is completely exhausted, the other living organisms like protozoa, fishes, algae etc. will not get oxygen for breathing and they die immediately. In the absence of oxygen no life is possible in water.
• Ultimately, the water body is not fit for any living organisms. Many industrial effluents has high BOD & its continuous discharge into any fresh water sources will make the water unfit for living things.

• This is the major reason for mass fish killings in fresh water bodies. The pollution effect due to heavy metals will also cause damage to living organisms but the process is slow.