After the Drain
Written by Studio AM.
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Half of a water system runs the other way. In a city with a sewer network, used water travels through a second set of pipes toward a treatment plant. Gravity carries much of the flow, while pumps lift it where needed.
What arrives is mostly water. The trouble is what is dissolved in it. Screens and settling tanks remove larger material and solids that can sink, but dissolved substances need other treatment.
One common treatment uses bacteria. Air is blown up through a long tank of wastewater, and a dense population of microbes breaks down organic waste and uses some of it to grow. Operators control this living process so that the microbes can work effectively. The living sludge is then left to settle, and some is returned to the aeration tank to maintain the population.
Further treatment, often including disinfection, may follow. Treated water can return to a river used by wildlife and downstream communities. It is not automatically drinking water. Release standards protect water quality, and any downstream drinking supply must receive the treatment it needs.
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Questions
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Question 1 of 4
What is the passage mainly about?
The answer is C: Microbes help treat wastewater, and the released water can affect downstream communities.
The passage explains a biological treatment step and why the quality of water released downstream matters.
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Question 2 of 4
What needs other treatment after screens and settling tanks?
The answer is A: Dissolved substances.
Screens and settling remove large or settleable solids, but dissolved substances need other treatment.
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Question 3 of 4
In this passage, material that is "dissolved" is
The answer is D: mixed into the water so completely that it cannot be strained out
Dissolved material is mixed into the water, unlike the larger material that screens can catch.
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Question 4 of 4
Why does wastewater treatment matter to people downstream?
The answer is B: Water released into the river can affect water they use.
The river connects the treatment plant with downstream communities, though their drinking water still needs appropriate treatment.
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