科学美国人60秒:去除下水道硫化物-托福听力下载

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　　Sewers are a marvel. They allow us to live close together without cities turning into smelly, disease-spreading swamps.

　　In a sewer's anaerobic conditions, common sulfate compounds are reduced by bacteria to hydrogen sulfide — the source of that rotten egg smell. And hydrogen sulfide when exposed to air forms sulfuric acid. Which eats away at concrete. The result: crumbling sewers.

　　The response has been to try to remove sulfide from sewage water. But researchers in Australia asked a different question: where does the original sulfate come from?

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　　Turns out much of it is from drinking water treatment. Aluminum sulfate is added at most Australian drinking water plants tested to coagulate solids out of the dirty water. That process is the source of more than half the resulting sulfates in the sewage. Numbers are similar in the U.S.

　　The scientists say that by switching to nonsulfate-based coagulants, governments worldwide could save a billion dollars a year in sewer repair costs. The research is in the journal Science.

　　Today, drinking water is managed separately from sewage treatment. A related editorial calls for a holistic approach to water management that looks at the entire water cycle, and helps save sewers in the process.

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