Waste water purification plant. Sealed tanks of the 'Living Machine', an ecologically-friendly water treatment system, at Ethel M's chocolate factory in Las Vegas, USA. The Living Machine mimics natural wetlands to clean up to 80,000 litres of waste water per day. On leaving the factory, the water enters these tanks, where it is aerated and grease-eating bacteria are introduced. The tanks are sealed to prevent odours escaping. The air is removed in underground pipes to a biological filter (not seen), where micro- organisms digest the compounds that cause the bad smells. The water is passed through further open tanks to complete the cleaning process.