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Environmental science · Solutions

Planet Fixers

Test a polluted lake, run a water-treatment plant, sort a recycling line, watch chlorine eat the ozone layer and decide which fixes really scale.

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The course

7 worlds · 29 lessons

World 1 · Clean Water

FREESources, test strips, treatment plants and disinfection
  1. 01Where does drinking water come from?Sources, pollutants and why we measure · 10 min
  2. 02Testing water: pH, hardness, chlorine and nitrateReading the numbers on a strip · 12 min
  3. 03Inside a treatment plantFive steps from river to reservoir · 11 min
  4. 04Killing the germs: disinfection and why home filters are not enoughChlorine, UV, ozone and the limits of a jug · 12 min

World 2 · Wastewater and Dead Zones

PROFish tanks, algal blooms, treatment plants and oxygen
  1. 01The nitrogen cycle in a fish tankAmmonia, nitrite and nitrate · 11 minPRO
  2. 02Too much food: eutrophicationAlgal blooms and oxygen crashes · 11 minPRO
  3. 03Treating wastewater: microbes at workPrimary, secondary and tertiary treatment · 11 minPRO
  4. 04Dissolved oxygen and BOD: reading a river's healthWarm water, thin air for fish · 11 minPRO

World 3 · Microplastics

PRODefinitions, sources, density and honest uncertainty
  1. 01How small is "micro"?Definitions, types and shapes · 10 minPRO
  2. 02Where do they come from?Tyres, textiles, paint and pellets · 11 minPRO
  3. 03Float or sink: density separationHow scientists pull plastic out of sand · 11 minPRO
  4. 04What we know and what we do notEvidence, uncertainty and sensible action · 11 minPRO

World 4 · Recycling Streams

PROThe waste hierarchy, sorting machines, material loops and compost
  1. 01Reduce, reuse, recycle: the waste hierarchyWhy the order matters · 10 minPRO
  2. 02Inside a sorting plantScreens, magnets, eddy currents and light · 11 minPRO
  3. 03Closing the loop: what recycling savesEnergy, quality and life-cycle thinking · 11 minPRO
  4. 04Compost and landfill: what happens to food wasteAir, heat and methane · 11 minPRO

World 5 · The Ozone Layer

PROThe shield, the chain reaction, the treaty and the other ozone
  1. 01A sunscreen in the skyOzone and the ultraviolet shield · 10 minPRO
  2. 02CFCs and the chlorine chainHow a stable gas breaks a fragile shield · 12 minPRO
  3. 03The hole and the treatyThe Antarctic hole and the Montreal Protocol · 12 minPRO
  4. 04Good up high, bad nearby: ground-level ozoneThe same molecule, a different place · 10 minPRO

World 6 · Air Quality

PROThe AQI, tiny particles, smog and the fixes that work
  1. 01What is in the air? Pollutants and the AQISeven pollutants and a colour scale · 11 minPRO
  2. 02Tiny particles, big effects: PM2.5 and healthSize decides where a particle goes · 11 minPRO
  3. 03Smog, wind and the inversion lidWhen the weather traps the pollution · 11 minPRO
  4. 04Cleaning the air: what actually worksFixes at the source · 12 minPRO

World 7 · Carbon Capture

PROScale, chemistry, energy and trade-offs
  1. 01How much is too much? The scale of the problemParts per million and billions of tonnes · 10 minPRO
  2. 02Capture at the smokestack: amine scrubbingChemistry that grabs CO₂ and lets it go · 11 minPRO
  3. 03Direct air capture and rock that eats CO₂Fans, sorbents and basalt · 12 minPRO
  4. 04Nature's way: trees, soils and oceansNatural sinks and their limits · 11 minPRO
  5. 05Choosing fixes: trade-offs on the Planet BoardNo single right answer, but better and worse questions · 12 minPRO