Environmental chemistry

• Types of Hardness


  • Temporary hardness that can be removed by boiling (HCO3 - hydrocarbonate ion)
  • Permanent hardness that cannot be removed by boiling (Ca2+, Mg2+)
• Hard water will not easily form a lather with soap, Ca2+ and Mg2+ ions form scum
• Soft water will easily form a lather with soap
• Removal of Temporary Hardness

  Ca(HCO3)2 → CaCO3 + CO2 + H2O
• Removal of Permanent Hardness

  Ion exchange resin (Ca2+, Mg2+ ions exchanged for Na+ ions)
• Water Analysis Methods


  • pH Analysis
  • Atomic Absorption Spectroscopy (AAS) for heavy metal concentration
  • Colorimetry for concentration of coloured substances
• Deionised water


  Has all dissolved ions removed, like distilled water
• Water Treatment Process


  1. Screening

  2. Flocculation with Aluminium Sulphate

  3. Settling

  4. Filtration (sand, rocks)

  5. Chlorination to kill bacteria

  6. Fluoridation

  7. pH adjustment to 7
• Biochemical Oxygen Demand (BOD)


  The amount of dissolved oxygen used up by organisms (in ppm) when a sample of water is left in the dark for 5 days at 20°C
• Sewage Treatment Stages


  • Primary (Physical)
  • Secondary (Biological) - Activated Sludge Process with aerobic bacteria
  • Tertiary (Chemical) - Removal of nitrates and phosphates
• Eutrophication


  The enrichment of water with nutrients, leading to the excessive growth of algae and other plants