Photo AI
The following flow chart shows the various stages of sewage treatment - Leaving Cert Chemistry - Question 11 - 2022
Question 11
The following flow chart shows the various stages of sewage treatment. Sewage and wastewater collection Primary treatment Secondary treatment Tertiary treatment ... show full transcript
Worked Solution & Example Answer:The following flow chart shows the various stages of sewage treatment - Leaving Cert Chemistry - Question 11 - 2022
Step 1
Describe one process carried out during primary treatment of sewage.
Answer
One process carried out during primary treatment of sewage is the use of grit channels, which include meshes and screens. This process is designed to remove large solid materials and insoluble matter from the sewage through physical means. Additionally, settlement tanks are often used to allow suspended solids to settle out, effectively removing sludge.
Step 2
What happens during secondary treatment?
Answer
During secondary treatment, organic matter in the sewage is oxidized. This is achieved by using biological processes, particularly through the action of microorganisms, which break down the organic matter, thereby reducing the overall biochemical oxygen demand (BOD) of the sewage.
Step 3
Step 4
What problem could occur if compounds of these elements were present in the treated water when it is released?
Answer
If phosphorus or similar compounds are present in the treated water upon release, it can lead to eutrophication. This is characterized by excessive plant growth or algal blooms, which can deplete oxygen levels (hypoxia) in the water. This depletion can severely impact aquatic life and may lead to fish kills and shellfish poisoning.
Step 5
Why is tertiary treatment not always carried out?
Answer
Tertiary treatment is not always carried out due to high costs associated with the process. Additionally, the concentration of nutrients, such as phosphates, may be low in treated water, making the treatment process less justifiable in certain scenarios.