Environmental Engineering in CE
Lagoons used for purification of polluted water

All of these
Are large shallow artificial lakes also known as clarification lakes, maturation ponds or oxidation ponds
Gives an excellent final effluent (with 3 to 4 lagoons arranged in series) having suspended solid < 1 mg/litre and BOD = 3.8 mg/litre
Use micro-organisms/bacteria in presence of dissolved oxygen

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