NPTEL Introduction to Environmental Engineering and Science-Ass8

A sedimentation tank designed to capture 0.015 mm diameter particles with a specific gravity of 2.65. If the sedimentation tank is designed for a surface overflow rate of 30 m3/day/m2. Find the efficiency of particle removal.

• 64.98 %

• 58.27 %

• 48.69 %

• 38.85 %

Find the length and width of the slow sand filter required to handle 3 MLD of water with a filtration rate of 150 lit/hr/m2. Assume Length: Width = 1:2.

• B=10.6 m, L= 11.2 m

• B=15.2, L=30.4

• B=20.5, L=41

• B=25 m, L=50 m

Find Cl2 demand, if Cl2 dose of 0.8 mg/L is added to have Cl2 residual of 0.3 mg/L. Find the dose of bleaching powder required if it contains only 20% of Cl2.

• Cl2 demand=0.4 mg/L, Bleaching powder dosage=2 mg/L

• Cl2 demand=0.2 mg/L, Bleaching powder dosage=3 mg/L

• Cl2 demand=0.4 mg/L, Bleaching powder dosage=5 mg/L

• Cl2 demand=0.5 mg/L, Bleaching powder dosage=4 mg/L

A 4 number of rapid sand filters treat 20 MLD of water with rate of filtration 4000 lit/hr/m2. Find the volume of filtered water required to backwash each filter, if backwashing rate is 5 times rate of filtration. Duration of backwash is 15 mins and it is carried out once in every 24 hours.

• 260.4 m3

• 153.9 m3

• 364.8 m3

• 230.1 m3

Which of the following statement(s) is/are true regarding rapid sand filters?

• a. A filter that operates continuously typically requires backwashing on a monthly basis.

• b. Large quantities of backwash water and sludge generated from filtration can be directly discharged to the environment.

• c. Because of the higher filtration rates, the area requirement of a rapid filtration plant is about 20% of that required for the slow sand filters.

• d. Operating a rapid sand filter requires trained personnel.

Which treatment process is designed for removing pathogens in a water treatment plant?

• a. Plain sedimentation

• b. Coagulation

• c. Filtration

• d. Disinfection

State whether the following statements are True/False. “The suspended particles tend to escape from the settling basin if the settling velocity exceeds the overflow rate.”

• a. True

• b. False

The design flow rate for a water supply system is;

• a. Equal to maximum day demand plus fire demand

• b. Equal to maximum hourly rate

• c. Maximum of Maximum day demand plus fire demand and Maximum hourly rate

• d. Minimum of Maximum day demand plus fire demand and Maximum hourly rate

Identify the correct order of chlorine forms in terms of their disinfecting strength.

• a. ClO2 > Free chlorines > Chloramines

• b. ClO2 > Chloramines > Free chlorines

• c. ClO2 = Free chlorines = Chloramines

• d. Free chlorines > ClO2 > Chloramines

Which of the following is not a coagulant?

• a. Aluminium sulphate

• b. Ferrous Sulphate

• c. Sodium hydroxide

• d. Sodium sulphate