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Difficulty: EasyPurification and Treatment of Water for Supply

In a municipal water treatment plant, raw river water undergoes several sequential processing stages to ensure it is safe for domestic consumption. Arrange the following key stages of municipal water purification in the correct chronological order from first to last.

  1. 1Screening to remove large floating debris and solids
  2. 2Coagulation by adding potash alum to clump fine colloidal clay particles
  3. 3Filtration through beds of coarse and fine sand
  4. 4Chlorination to destroy pathogenic microorganisms

Answer

The correct sequence of municipal water treatment stages from start to finish is: Screening to remove large floating debris, followed by Coagulation using alum to clump fine particles, then Sand filtration to remove tiny remaining suspended solids, and finally Chlorination to kill disease-causing germs.
The correct sequence follows the standard municipal waterworks workflow: physical removal of large debris (Screening) →\rightarrow chemical aggregation of clay suspensions (Coagulation) →\rightarrow mechanical straining of micro-solids (Filtration) →\rightarrow chemical destruction of disease-causing bacteria (Chlorination).

Step-by-Step Solution

1
Identify the primary intake step.
Screening is the initial physical process to filter out large objects like leaves and sticks.
Large debris must be removed first to protect pump machinery and piping.
2
Identify the chemical clumping step.
Coagulation involves adding chemical coagulants such as alum to bind fine suspended clay particles into larger flocs.
Fine particles will not settle or filter easily without prior coagulation.
3
Identify the physical clarification step.
Filtration passes water through sand and gravel layers to remove remaining micro-suspended matter.
Water must be visually clear before chemical disinfection so pathogens are fully exposed to chlorine.
4
Identify the final disinfection step.
Chlorination is carried out last to kill bacteria and ensure biological safety for drinking.
Adding chlorine last ensures residual disinfection in the municipal piping network.

Key Concept

Sequential Stages of Municipal Water Purification
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Topics

Purification and Treatment of Water for Supply

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