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Where does the salt go in reverse osmosis?

A reverse-osmosis system produces both water that passes through a membrane and a more concentrated stream left behind. Pressure drives the separation, so describing only the treated output leaves part of the process unseen.

4–5 min

Questions you could explore

  • Why does the system need both an input and two outputs?
  • What affects how well a membrane separates particular substances?

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Environment and climate

What can tree rings reveal about past climate?

A tree keeps a record of growth in its wood, but reading that record as climate history takes more than counting rings. Moisture, temperature, and other growing conditions can leave overlapping clues.

4–5 min

What can tree rings reveal about past climate?

Environment and climate4–5 minA tree keeps a record of growth in its wood, but reading that record as climate history takes more than counting rings. Moisture, temperature, and other growing conditions can leave overlapping clues.

Environment and climate

Why can a city be warmer than nearby countryside?

The trip from a leafy edge of town to a dense street can also be a trip between different temperatures. Buildings, pavement, vegetation, and waste heat all affect the balance, and the contrast changes with weather and time of day.

3–5 min

Why can a city be warmer than nearby countryside?

Environment and climate3–5 minThe trip from a leafy edge of town to a dense street can also be a trip between different temperatures. Buildings, pavement, vegetation, and waste heat all affect the balance, and the contrast changes with weather and time of day.

Environment and climate

A trip through a wastewater treatment plant

Water disappearing down a drain begins another journey before it reaches a river or the sea. Uisce Éireann's description of treatment in Ireland separates several different jobs, from screening out objects to biological treatment; the resulting effluent is not drinking water.

4–5 min

A trip through a wastewater treatment plant

Environment and climate4–5 minWater disappearing down a drain begins another journey before it reaches a river or the sea. Uisce Éireann's description of treatment in Ireland separates several different jobs, from screening out objects to biological treatment; the resulting effluent is not drinking water.

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