Water requirements miscellaneous
Direction: A plain sedimentation tank with a length of 20 m, width of 10 m and a depth of 3 m is used in a water treatment plant to treat 4 million litres of water per day (4 MLD). The average temperature of water is 20°C. The dynamic viscosity of water is 1.002 × 10–3 N.s/m² at 20°C. Density of water is 998.2 kg/M³. Average specific gravity of particles is 2.65.
- What is the minimum diameter of the particle which can be removed with 100% efficiency in the above sedimentation tank?
-
View Hint View Answer Discuss in Forum
For 100% removal, settling velocity = SOR
Settling velocity, Vs = 9 (S - 1)d² 18 v = 9 ρ (S - 1)d² 18 μ ∴ d = √ Vs × 18 × μ g.ρ(S - 1) Vs = SOR = 20 m³/m²/day = 20 × 10³ = 0.2315 mm/s 24 × 60 × 60 d = √ .2315 × 18 × 1.002 × 10-3 = 1.606 × 10–5m = 16 × 10–3mm. 9.81 × (2.65 - 1) × 1000 Correct Option: B
For 100% removal, settling velocity = SOR
Settling velocity, Vs = 9 (S - 1)d² 18 v = 9 ρ (S - 1)d² 18 μ ∴ d = √ Vs × 18 × μ g.ρ(S - 1) Vs = SOR = 20 m³/m²/day = 20 × 10³ = 0.2315 mm/s 24 × 60 × 60 d = √ .2315 × 18 × 1.002 × 10-3 = 1.606 × 10–5m = 16 × 10–3mm. 9.81 × (2.65 - 1) × 1000
Direction: Following chemical species were reported for water sample from a well: 
- Total hardness in mg/l as CaCO3 is
-
View Hint View Answer Discuss in Forum
NA
Correct Option: B
NA
- A town has an existing horizontal flow sedimentation tank with an overflow rate of 17m³ /day/m², and it is desirable to remove particles that have settling velocity of 0.1 mm/s. Assuming the tank is an ideal sedimentation tank, the percentage of particles removal is approximately equal to
-
View Hint View Answer Discuss in Forum
% particle removed = efficiency,
η = Vs × 100 = 0.1 × 100 V0 
17 × 1000 
24 × 3600
= 50.8%Correct Option: B
% particle removed = efficiency,
η = Vs × 100 = 0.1 × 100 V0 17 × 1000 24 × 3600
= 50.8%
- The following chemical is used for coagulation
-
View Hint View Answer Discuss in Forum
NA
Correct Option: D
NA
