What is the correct sequence, from initial to final, of surface waste water treatment?

1.Disinfection

2.Sedimentation

3.Filtration

4.Screening

A1, 2, 3, 4

B1, 2, 4, 3

C4, 2, 1, 3

D4, 2, 3, 1 ✓ Correct

Correct answer: (D) 4, 2, 3, 1

Explanation

Surface wastewater treatment runs from screening first, through sedimentation and filtration, to disinfection last.

Statement 4, screening, comes first to remove large floating solids.

Statement 2, sedimentation, follows so suspended particles settle out.

Statement 3, filtration, then removes finer remaining particles.

Statement 1, disinfection, is the final step to kill remaining microbes.

Chlorine, ozone or ultraviolet light is commonly used for the final disinfection.

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