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Answer any two of the parts (a), (b) and (c) - Leaving Cert Chemistry - Question 10 - 2020
Question 10
Answer any two of the parts (a), (b) and (c). (a) Biochemical oxygen demand (BOD) of wastewater is lowered in sewage treatment by decreasing the quantities of suspe... show full transcript
Worked Solution & Example Answer:Answer any two of the parts (a), (b) and (c) - Leaving Cert Chemistry - Question 10 - 2020
Step 1
Define BOD.
Answer
Biological Oxygen Demand (BOD) is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water. It is an important indicator of water pollution, as higher BOD levels suggest greater amounts of biodegradable material present in the water.
Step 2
What happens during the primary stages of sewage treatment?
Answer
During the primary stage of sewage treatment, physical processes are used to remove large solids and particulate matter from wastewater. This typically involves screening, sedimentation, and flotation methods to separate heavier solids from lighter materials, resulting in primary sludge.
Step 3
What happens during the secondary stages of sewage treatment?
Answer
In the secondary stage, biological processes are employed to further degrade organic material. Microorganisms break down the remaining organic matter in aerated tanks or bioreactors, converting it into biomass, which can be separated from the treated water.
Step 4
Under what circumstances is tertiary treatment considered desirable?
Answer
Tertiary treatment is considered desirable in situations where the treated wastewater is to be reused for irrigation, industrial processes, or where it is discharged into sensitive ecosystems requiring high quality water. It focuses on removing nutrients, pathogens, and residual chemicals.
Step 5
Why is tertiary treatment not always carried out, even when desirable?
Answer
Tertiary treatment may not always be carried out due to high costs, lack of technology or infrastructure, or insufficient regulations enforcing water quality standards. Additionally, the economic viability of wastewater reuse can be a deciding factor.
Step 6
What could a negative environmental impact be if tertiary treatment were not carried out where desirable?
Answer
If tertiary treatment is not conducted where desired, this could lead to the release of nutrient-rich effluents into waterways, resulting in eutrophication. This process can cause algal blooms, decreasing oxygen levels in the water, harming aquatic life, and affecting overall ecosystem health.