GATE CE topic:water-and-wastewater-treatment PYQs & Answers — Page 3

Questions 21–30 of 81. Imported answers require independent review unless marked reviewed.

A hypothetical multimedia filter, consisting of anthracite particles (specific gravity: 1.50), silica sand (specific gravity: 2.60), and ilmenite sand (specific gravity: 4.20), is to be designed for treating water/wastewater. After backwashing, the particles should settle forming three layers: coarse anthracite particles at the top of the bed, silica sand in the middle, and small ilmenite sand particles at the bottom of the bed.

Assume (i) Slow discrete settling (Stoke’s law is applicable) (ii) All particles are spherical (iii) Diameter of silica sand particles is 0.20 mm

The CORRECT option fulfilling the diameter requirements for this filter media is

Your answerChoose one option.

diameter of anthracite particles is slightly less than 0.35 mm and diameter of ilmenite particles is slightly greater than 0.141 mm.

diameter of anthracite particles is slightly greater than 0.35 mm and diameter of ilmenite particles is slightly less than 0.141 mm.

diameter of anthracite particles is slightly less than 0.64 mm and diameter of ilmenite particles is slightly less than 0.10 mm.

diameter of anthracite particles is slightly greater than 0.64 mm and diameter of ilmenite particles is slightly less than 0.10 mm.

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Activated carbon is used to remove a pollutant from wastewater in a mixed batch reactor, which follows first-order reaction kinetics.

At a reaction rate of 0.38 /day, the time (in days) required to remove the pollutant by 95% is ____________ (rounded off to 1 decimal place).

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A circular settling tank is to be designed for primary treatment of sewage at a flow rate of 10 million liters/day. Assume a detention period of 2.0 hours and surface loading rate of 4000 liters/m

/day. The height (in meters) of the water column in the tank is ______________ (rounded off to 2 decimal places).

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A water treatment plant treats 25 MLD water with a natural alkalinity of 4.0 mg/L (as CaCO₃). It is estimated that, during coagulation of this water, 450 kg/day of calcium bicarbonate (Ca(HCO₃)₂) is required based on the alum dosage.

Consider the atomic weights as: Ca-40, H-1, C-12, O-16.

The quantity of pure quick lime, CaO (in kg) required for this process per day is__________ (rounded off to 2 decimal places).

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Identify the waterborne diseases caused by viral pathogens:

Your answerSelect all correct options. You can choose more than one.

Acute anterior poliomelitis

Cholera

Infectious hepatitis

Typhoid fever

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Which of the following is/are NOT active disinfectant(s) in water treatment?

Your answerSelect all correct options. You can choose more than one.

•OH (hydroxyl radical)

O₃ (ozone)

OCl⁻ (hypochlorite ion)

Cl⁻ (chloride ion)

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In the following table, identify the correct set of associations between the entries in Column-1 and Column-2.

Column-1	Column-2
P: Reverse Osmosis	I: Ponding
Q: Trickling Filter	II: Freundlich Isotherm
R: Coagulation	III: Concentration Polarization
S: Adsorption	IV: Charge Neutralization

Your answerChoose one option.

P-II, Q-I, S-III

Q-III, R-II, S-IV

P-IV, R-I, S-II

P-III, Q-I, R-IV

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In the context of water and wastewater treatments, the correct statements are:

Your answerSelect all correct options. You can choose more than one.

particulate matter may shield microorganisms during disinfection

ammonia decreases chlorine demand

phosphorus stimulates algal and aquatic growth

calcium and magnesium increase hardness and total dissolved solids

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A flocculator tank has a volume of 280 m³. The temperature of water in the tank is 15°C, and the average velocity gradient maintained in the tank is 100/s. The temperature of water is reduced to 5°C, but all other operating conditions including the power input are maintained as the same. The decrease in the average velocity gradient (in %) due to the reduction in water temperature is ______________ (round off to nearest integer).

[Consider dynamic viscosity of water at 15°C and 5°C as 1.139×10⁻³ N-s/m² and 1.518×10⁻³ N-s/m², respectively]

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The wastewater inflow to an activated sludge plant is 0.5 m³/s, and the plant is to be operated with a food to microorganism ratio of 0.2 mg/mg-d. The concentration of influent biodegradable organic matter to the plant (after primary settling) is 150 mg/L, and the mixed liquor volatile suspended solids concentration to be maintained in the plant is 200 mg/L. Assuming that complete removal of biodegradable organic matter in the tank, the volume of aeration tank (in m³, in integer) required for the plant is ________________.

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GATE CE topic:water-and-wastewater-treatment PYQs

Question 42

Question 60

Question 60

Question 61

Question 27

Question 29

Question 45

Question 48

Question 63

Question 64