Sewage Treatment
Introduced| English | Meaning |
|---|---|
| sewage/ˈsuːɪdʒ/ | Wastewater containing human waste and other materials carried away from buildings. |
| primary/ˈpraɪməri/ | primary |
| sludge/slʌdʒ/ | sludge |
| secondary/ˈsekəndəri/ | secondary |
| bacteria/bækˈtɪərɪə/ | Single-celled prokaryotic organisms whose cells lack a membrane-bound nucleus. |
Cleaning our dirty water
- Every home sends sewage 污水 down the drain.
- Toilets, sinks, and showers all add to it.
- Released raw, it would spread disease and pollution.
- So it passes through a treatment plant first.
Primary: remove the solids
- First, screens catch big trash, rags, and grit.
- Then the water sits in settling tanks.
- Heavy solids sink to the bottom as sludge 污泥.
- This physical step is called primary 一级 treatment.
Treating water to make it safe: sedimentation, filtration, then disinfection
Sewage is…
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Sewage is dirty wastewater from toilets, sinks, and drains that must be cleaned before release.
Secondary: bacteria do the work
- The water still holds dissolved organic waste.
- In secondary 二级 treatment, bacteria 细菌 digest it.
- The microbes break the waste into harmless substances.
- This biological step cleans most of what remains.
How sewage is cleaned
Follow dirty water through the stages that make it safe to release.
In primary treatment, solids are removed by…
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Primary treatment lets heavy solids sink to the bottom as sludge, and skims floating material off the top.
In secondary treatment, ____ break down the dissolved organic waste.
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Secondary treatment uses bacteria to digest the organic matter left in the water.
Final: disinfect and release
- The water is now clear but may still carry germs.
- A final step disinfects it with chlorine or UV light.
- Advanced plants also remove leftover nutrients.
- The clean water is then safely released to a river or sea.
The final stage often disinfects the water to kill disease-causing germs.
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A final disinfection step (chlorine or UV) kills pathogens before the water is released.
Put the stages in order — select the first three to happen.
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Screen → settle → bacteria digest → disinfect and release. Clean water is never sent back dirty.
Notice the two very different kinds of cleaning. Primary treatment is physical — just letting solids settle and screening trash out. Secondary is biological — living bacteria eat the dissolved waste. Skipping secondary treatment (as some places do) leaves the water still loaded with organic matter that will cause eutrophication downstream. Both stages matter.
From toilet to river:
- The sewage reaches the plant and is screened, then sits in tanks where sludge settles out (primary).
- The cleared water flows to aeration tanks where bacteria digest the dissolved waste (secondary).
- Finally it is disinfected and released to the river — clear, low in nutrients, and safe for the fish downstream.
Sewage treatment cleans wastewater in stages. Primary (physical) screens trash and settles solids as sludge. Secondary (biological) uses bacteria to digest dissolved organic waste. A final step disinfects the water and removes nutrients before it is safely released. Both the physical and biological stages are needed.