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Waste water undergoes sewage treatment before discharge into rivers, lakes or the sea - Leaving Cert Chemistry - Question a - 2017
Question a
Waste water undergoes sewage treatment before discharge into rivers, lakes or the sea. (i) How are most of the suspended solid wastes removed during sewage treatmen... show full transcript
Worked Solution & Example Answer:Waste water undergoes sewage treatment before discharge into rivers, lakes or the sea - Leaving Cert Chemistry - Question a - 2017
Step 1
How are most of the suspended solid wastes removed during sewage treatment?
Answer
Most suspended solid wastes are removed during the primary treatment phase of sewage treatment. This phase involves mechanical processes such as screening, settling, and the use of grit channels. Solid materials are separated from the liquid waste, allowing for the majority of large particles to settle out.
Step 2
Describe what happens during the secondary treatment of sewage.
Answer
During secondary treatment, a biological process occurs where microbes like bacteria, fungi, and decomposers break down organic matter in the sewage. This process typically involves aerobic digestion, where oxygen is introduced through aeration and agitation to facilitate the microbial activity. The microbes consume the organic pollutants, converting them into simpler substances, thereby reducing the biochemical oxygen demand (BOD) and improving water quality.
Step 3
At what stage of sewage treatment are nitrates and phosphates removed?
Answer
Nitrates and phosphates are removed during the tertiary treatment stage, which is the final phase of sewage treatment. This stage involves advanced processes that target remaining nutrients and ensure water quality meets environmental standards before the effluent is discharged.
Step 4
What could happen in a lake as the result of the addition of large quantities of nitrates and phosphates?
Answer
The addition of large quantities of nitrates and phosphates to a lake can lead to eutrophication, which creates an imbalance in the aquatic ecosystem. This results in excessive growth of algae, leading to algal blooms. As these algae die and decompose, it creates a depletion of oxygen in the water, which can result in fish kills, the production of smelly water, or the occurrence of pollution. The overall health of the aquatic environment is compromised.