Effluent Treatment Methods
Method
Treating Chemicals
Ph
Reaction Time min
Remarks
Cr+6 reduction
Sodium Metabisulfite Ferrous sulphate
2.3-2.6
30
 Ferrous salts produce 4 times more sludge than bisulfite.
Cyanide oxidation to cynate
Chlorine Sodium Hypochlorite (15%) Calcium Hypochlorite
11
60
  
Cyanate oxidation to co2 & N2
Chlorine Sodium Hypochlorite (15%) Calcium Hypochlorite
8.5
60
  
Metal Precipitation As hydroxide
NaOH Ca(OH)2
7.5-10.00
30
Optimum pH varies with metal to be removed. Ca produces 3 times more sludge than Na.
As sulfide
FeS/Na2S
8.0-9.0
20
 For polishing after hydroxide precipitation
Carbonate
NaHCO3
Variable
30
 Food for pH, cd and Ni removal.
Insoluble Starch gums
7
 Fast precipitation, works with the presence of some complexing agent. Polishing after hydroxide.
Oily waste
H₂SO₄ Polyelectrolytes Alum Calcium Chlorid>
3.0
3.0-50
3
3
10-20
 Removal depends on oils.
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