D56 MASTER THE DAY

Which process removes fine suspended and colloidal particles from water after sedimentation?

• Screening
• Aeration
• Filtration
• Coagulation

Answer explanation

Filtration removes very fine colloidal and suspended particles after sedimentation.

Which coagulant is most commonly used in water treatment?

• Ferric chloride
• Alum
• Sodium aluminate
• Copperas

Answer explanation

Alum (Aluminum sulphate) is the most commonly used coagulant.

In slow sand filters, what is the effective size of sand particles?

• 0.2–0.4 mm
• 0.35–0.55 mm
• 0.55–0.70 mm
• 1.0–1.5 mm

Answer explanation

Slow sand filters use sand particles with effective size between 0.2–0.4 mm.

Which method is used for cleaning rapid sand filters?

• Scraping
• Boiling
• Backwashing
• Chemical treatment

Answer explanation

Backwashing is used for cleaning rapid sand filters.

Which disinfectant method is most commonly used in public water supplies?

• Ozonation
• Boiling
• UV rays
• Chlorination

Answer explanation

Chlorination is widely used for disinfecting public water supplies due to cost and effectiveness.

The pH range suitable for Alum as a coagulant is:

• 4.0 – 5.5
• 6.5 – 8.5
• 8.5 – 10
• 5.0 – 6.0

Answer explanation

Alum works best in a pH range of 6.5–8.5.

What is the cleaning method in a slow sand filter?

• Backwashing
• Scraping
• Lime addition
• Blowing air

Answer explanation

Slow sand filters are cleaned by scraping the top layer of sand.

Which of the following is not removed by boiling water?

• Bacteria
• Temporary hardness (Ca)
• Permanent hardness
• Cholera organisms

Answer explanation

Boiling removes bacteria and temporary hardness but not permanent hardness.

What is the rate of filtration for rapid sand filters?

• 100–200 L/hr/m²
• 300–500 L/hr/m²
• 3000–6000 L/hr/m²
• 6000–15000 L/hr/m²

Answer explanation

Rapid sand filters have a filtration rate of 3000–6000 L/hr/m².

Which process is suitable for removing salt from seawater?

• Zeolite process
• Demineralization
• Reverse osmosis
• Boiling

Answer explanation

Reverse osmosis is a common method for desalination of seawater.