Water treatment

• Water Covers 70% – 75% of the earth surface
• Total water available is 1400 million km3
• 97% – locked in sea or oceans (1332 million km3)
• 3% – fresh water
• 2.15% in polar ice caps (29.20 million km3)
• < 1% available as surface water (rivers, streams, lakes) with which we must manage ourselves!
• Only 14 million km3 is fresh water
• Oceans receive about 61% & land 39% of total rainfall
• No plant or animal species can survive without water
• If water in our body drops by 1%, we feel thirst, if it drops by 10%, we face death
• Water is a renewable resource; It may change it's form but quantity of water on earth has remained same for millions of years
• One of the greatest challenges facing the world!
• Water usage breakdown


  • agriculture (70%)
  • industry (22%)
  • domestic (9%)
• Water uses in India

  • agriculture (87%)
  • industry (8%)
  • domestic (5%)
• Types of Impurities Present in water

  • Micro-organisms (Bacteria, Fungi, algae and other forms of animal and plant life)
  • Suspended impurities (Inorganic (e.g., clay and sand), Organics (e.g., oil, vegetable and animal matters))
  • Colloidal impurities (Clay and finely divided silica colloidal particles of 10-4 – 10-6 mm size)
  • Dissolved impurities (Inorganic salts (Cations: Ca2+, Mg2+, Na+, K+, Fe2+, Al3+, Zn2+, Cu2+, Anions: Cl-, SO42-, NO3-, HCO3-, F-, NO2-), Gases: CO2, O2, N2, NH3, H2S, Organics salts)
• Hardness of water


  Soap consuming capacity of a water sample, mainly due to the certain salt of calcium (Ca2+), magnesium (Mg2+) and other heavy metals dissolved in it
• Hardness of water


  • Other metal ions such as Fe2+, Mn2+, Al3+ also contributes to hardness, but they are present in water only in traces
  • Calcium and magnesium react with the sodium salts of long chain fatty acid present in the soap to form insoluble scums of calcium and magnesium soaps
• Temporary hardness


  Caused by the presences of dissolved bicarbonate of calcium and magnesium and other heavy metal ions, mostly destroyed by boiling of water
• Permanent hardness (non-carbonate hardness)

  Due the presences of chlorides, nitrates, and sulphates of calcium, magnesium, iron and other heavy metal ions
• Measurement of hardness


  Expressed in terms of equivalent of calcium carbonate because it is an insoluble salt that can be most easily precipitated in water treatment
• Units of Hardness


  ppm or mg/L, Degree Clarke (°Cl), Degree French (°Fr)
• Chemical analysis - Estimation of hardness

  1. Soap solution method (Standardization, Determination of total hardness, Determination of permanent hardness)

  2. EDTA method (Standardization of EDTA, Total hardness, Permanent hardness, Temporary hardness)

  
• CH2COOH


  Chemical formula
• NaOOCH2C


  Chemical formula
• HOOCH2C


  Chemical formula
• O2N


  Chemical formula
• N


  Chemical formula
• O


  Chemical formula
• NaO3S


  Chemical formula
• Ca/Mg


  Chemical formula
• EDTA method


  Analytical method
• CH2


  Chemical formula
• Requirements for EDTA method

  • Standard hard water
  • EDTA solution
  • Indicator
  • Buffer solution
• EDTA method


  1. Standardization of EDTA

  2. Total hardness

  3. Permanent hardness

  4. Temporary hardness
• 1 ml 0.01 M EDTA ≡ 1 mg CaCO3
• Hardness determination methods


  • Soap solution method
  • EDTA method

  
• Hardness ranges and effects

  • 300-500 ppm: excessive hardness
  • 150 ppm: consumer objection
  • 60-120 ppm: moderate amount
• Boiler water hardness limits

  • Hardness: < 0.2 ppm
  • Caustic alkalinity (OH-): 0.15 - 0.45 ppm
  • Soda alkalinity (CO3^2-): 0.45 - 1 ppm
• Otherwise, scale & sludge formation, embrittlement, corrosion, foaming happens
• Hardness causing ions


  • Ca, Mg
  • Fe, Mn, St, Al salts