Waste Water Treatment & Alternative Methods of Extracting Metals

Waste water treatment

• Homes and industry produce large amounts of waste water that must be treated before it is released into the environment
• Sewage and agricultural waste water need organic matter and harmful microbes removed. Industrial waste water may also contain harmful chemicals that need removing
• Sewage treatment, in order:
  • Screening and grit removal: a metal grid removes large solids and grit
  • Sedimentation: the water stands in a tank so solids settle out as sewage sludge, leaving liquid effluent on top
  • The sludge is treated by anaerobic digestion: bacteria break down the organic matter without oxygen, producing methane (biogas) that can be burned for energy, and fertiliser
  • The effluent is treated by aerobic biological treatment: air is bubbled through so bacteria break down the remaining organic matter and harmful microbes, then it is released into rivers

• Ease of obtaining potable water: ground water is the easiest (only filtering and sterilising); waste water needs many stages; salt water needs the most energy. Waste and salt water are only used where fresh water is short