Environmental Engineering in CE
Noise produced by cooling fans (employed in air cooled heat exchangers or cooling tower) is mainly caused due to the turbulence created by blade passage through air. It can be reduced by use of a slower fan

Neither A nor B
With greater number of blades
Of increased diameter
Both A & B

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Environmental Engineering in CE
Lagoons used for purification of polluted water

Use micro-organisms/bacteria in presence of dissolved oxygen
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
All of these
Are large shallow artificial lakes also known as clarification lakes, maturation ponds or oxidation ponds

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