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Water and Wastewater Quality and Treatment(24)Air Pollution(5)Municipal Solid Wastes(4)

Water and Wastewater Quality and Treatment

24 Questions

GATE→2026→Environmental Engineering→Water and Wastewater Quality and Treatment

Q1

MCQ[1 Mark]

A rapid sand filter bed of depth 0.8 m has 40% porosity during service cycle. Recommended backwash expanded porosity is 70%. The uniform expanded depth (in m) during backwash is

(A)

1.0

(B)

1.2

(C)

1.4

(D)

1.6

Explanation

GATE→2026→Environmental Engineering→Water and Wastewater Quality and Treatment

Q2

MCQ[1 Mark]

The settling velocity of inorganic particles in the sedimentation tank of a water treatment plant is governed by

(A)

Darcy's law

(B)

Stokes' law

(C)

Dupuit's law

(D)

Bernoulli's law

Explanation

GATE→2026→Environmental Engineering→Water and Wastewater Quality and Treatment

Q3

MSQ[1 Mark]

Which of the following components is/are NOT removed in the secondary treatment of sewage?

(A)

Suspended settleable organic solids

(B)

Colloids including dissolved organic matter

(C)

Pathogens

(D)

Fat and grease

Explanation

GATE→2026→Environmental Engineering→Water and Wastewater Quality and Treatment

Q4

MCQ[2 Marks]

Average sewage from a city is 90 MLD and BOD5 is 300 mg/L. Standard domestic BOD5 per person is 0.08 kg/day. The population equivalent is

(A)

337500

(B)

216000

(C)

270000

(D)

168750

Explanation

GATE→2026→Environmental Engineering→Water and Wastewater Quality and Treatment

Q5

NAT[2 Marks]

Activated Sludge Process parameters provided. To maintain equilibrium, the flowrate (in $\text{m}^3/\text{day}$) of sludge to be wasted from the system is

Explanation

GATE→2025→Environmental Engineering→Water and Wastewater Quality and Treatment

Q6

MCQ[1 Mark]

Fecal Coliform concentration in river water was 10780 cfu/100 ml, reduced to 23 cfu/100 ml before chlorination. Log Kill is closest to

(A)

4.00

(B)

2.50

(C)

2.67

(D)

3.00

Explanation

GATE→2025→Environmental Engineering→Water and Wastewater Quality and Treatment

Q7

MSQ[1 Mark]

Surface Overflow Rate is 45 m3/m2/d. Minimum diameters of spherical inorganic and organic particles completely removed using Stokes' law are evaluated. Correct options are

(A)

Option A

(B)

Option B

(C)

Option C

(D)

Option D

Explanation

GATE→2025→Environmental Engineering→Water and Wastewater Quality and Treatment

Q8

MSQ[1 Mark]

Identify the pollutant(s) where aeration is employed as a part of their removal:

(A)

Iron

(B)

Cadmium

(C)

Manganese

(D)

Zinc

Explanation

GATE→2025→Environmental Engineering→Water and Wastewater Quality and Treatment

Q9

MSQ[2 Marks]

$MgCl_2$ and $CaSO_4$ added to water. TDS = 500 mg/L, Total Hardness = 400 mg/L as $CaCO_3$. Which option is/are true:

(A)

Amount of MgCl2 added is 143 mg

(B)

Amount of CaSO4 added is 357 mg

(C)

Amount of MgCl2 added is 103 mg

(D)

Amount of CaSO4 added is 397 mg

Explanation

GATE→2025→Environmental Engineering→Water and Wastewater Quality and Treatment

Q10

MSQ[2 Marks]

A facultative pond system is employed for wastewater treatment. Which of the following statements is/are true:

(A)

Dissolved oxygen concentration will be high during daytime compared to night-time

(B)

pH will be high during daytime compared to night-time

(C)

Dissolved oxygen concentration will be low during daytime

(D)

pH will be low during daytime

Explanation

GATE→2024→Environmental Engineering→Water and Wastewater Quality and Treatment

Q11

NAT[2 Marks]

Activated carbon removes pollutant in mixed batch reactor with first-order rate 0.38 /day. Time (in days) required to remove 95% of pollutant is

Explanation

GATE→2024→Environmental Engineering→Water and Wastewater Quality and Treatment

Q12

NAT[2 Marks]

A water treatment plant treats 25 MLD water with natural alkalinity 4.0 mg/L as $CaCO_3$. $450\text{ kg/day}$ of $Ca(HCO_3)_2$ is required based on alum dosage. Quantity of pure quick lime CaO (in kg) per day is

Explanation

GATE→2023→Environmental Engineering→Water and Wastewater Quality and Treatment

Q13

MSQ[1 Mark]

Identify the waterborne diseases caused by viral pathogens:

(A)

Acute anterior poliomyelitis

(B)

Cholera

(C)

Infectious hepatitis

(D)

Typhoid fever

Explanation

GATE→2023→Environmental Engineering→Water and Wastewater Quality and Treatment

Q14

MCQ[2 Marks]

Match Column 1 (P: Reverse Osmosis, Q: Trickling Filter, R: Coagulation, S: Adsorption) with Column 2 (I: Ponding, II: Freundlich Isotherm, III: Concentration Polarization, IV: Charge Neutralization).

(A)

P-II, Q-I, S-III

(B)

P-III, R-II, S-IV

(C)

P-IV, R-I, S-II

(D)

P-III, Q-I, R-IV

Explanation

GATE→2023→Environmental Engineering→Water and Wastewater Quality and Treatment

Q15

NAT[2 Marks]

Flocculator tank volume $2800\text{ m}^3$, temp $15^{\circ}\text{C}$, $G = 100/\text{s}$. Temperature reduced to $5^{\circ}\text{C}$ with constant power input. Decrease in velocity gradient (%) is

Explanation

GATE→2023→Environmental Engineering→Water and Wastewater Quality and Treatment

Q16

NAT[2 Marks]

Activated sludge plant inflow $0.5\text{ m}^3/\text{s}$, F/M ratio $0.2\text{ day}^{-1}$, influent BOD $150\text{ mg/L}$, MLVSS $2000\text{ mg/L}$. Volume of aeration tank (in $\text{m}^3$) is

Explanation

GATE→2022→Environmental Engineering→Water and Wastewater Quality and Treatment

Q17

MCQ[1 Mark]

Total hardness in raw water is $500\text{ mg/L}$ as $CaCO_3$. Expressed in milligram equivalent per liter (meq/L) is

(A)

10

(B)

100

(C)

1

(D)

5

Explanation

GATE→2022→Environmental Engineering→Water and Wastewater Quality and Treatment

Q18

MSQ[1 Mark]

For wastewater from wood pulping industry, COD and BOD5 determined. Which statement(s) is/are correct?

(A)

COD > BOD5

(B)

COD != BOD5

(C)

COD < BOD5

(D)

COD = BOD5

Explanation

GATE→2022→Environmental Engineering→Water and Wastewater Quality and Treatment

Q19

MSQ[1 Mark]

Which of the following process(es) can be used for conversion of salt water into fresh water?

(A)

Microfiltration

(B)

Electrodialysis

(C)

Ultrafiltration

(D)

Reverse osmosis

Explanation

GATE→2022→Environmental Engineering→Water and Wastewater Quality and Treatment

Q20

MCQ[2 Marks]

Henry's law constant for $O_2$ is $1.3\text{ mmol/(L-atm)}$. Atmospheric partial pressure of $O_2$ is $0.21\text{ atm}$. Dissolved oxygen concentration (in mg/L) is

(A)

8.7

(B)

0.8

(C)

198.1

(D)

0.2

Explanation

GATE→2022→Environmental Engineering→Water and Wastewater Quality and Treatment

Q21

MCQ[2 Marks]

Water sample has $Ca^{2+} = 100\text{ mg/L}$, $Mg^{2+} = 36\text{ mg/L}$, $HCO_3^- = 122\text{ mg/L}$. Total hardness and temporary hardness (in mg/L as $CaCO_3$) are

(A)

400 and 100

(B)

400 and 300

(C)

500 and 100

(D)

800 and 200

Explanation

GATE→2022→Environmental Engineering→Water and Wastewater Quality and Treatment

Q22

NAT[2 Marks]

Wastewater sample has $34\text{ mg } NH_3/\text{L}$ and $6.2\text{ mg } NO_3^-/\text{L}$. Total nitrogen concentration (in mg N/L) is

Explanation

GATE→2022→Environmental Engineering→Water and Wastewater Quality and Treatment

Q23

NAT[2 Marks]

A 2% sewage sample incubated for 3 days at $27^{\circ}\text{C}$ showed 10 mg/L DO depletion. BOD rate constant $k = 0.23\text{ day}^{-1}$ (base e). Ultimate BOD (in mg/L) is

Explanation

GATE→2022→Environmental Engineering→Water and Wastewater Quality and Treatment

Q24

NAT[2 Marks]

Sedimentation basin depth 3 m, width 5 m, length 40 m. Inflow $500\text{ m}^3/\text{h}$. Removal fraction of particles with settling velocity $1.0\text{ m/h}$ is

Explanation

Air Pollution

5 Questions

GATE→2025→Environmental Engineering→Air Pollution

Q25

MCQ[1 Mark]

Hydrocarbon ($C_n H_m$) is burnt in air. Stoichiometric fuel to air mass ratio for this process is given by

(A)

$0.0291 \frac{4n+m}{12n+m}$

(B)

$34.42 \frac{12n+m}{4n+m}$

(C)

$34.42 \frac{4n+m}{12n+m}$

(D)

$0.0291 \frac{12n+m}{4n+m}$

Explanation

GATE→2024→Environmental Engineering→Air Pollution

Q26

MSQ[1 Mark]

The primary air pollutant(s) is/are

(A)

Sulphur dioxide

(B)

Sulphuric acid

(C)

Nitric oxide

(D)

Ozone

Explanation

GATE→2024→Environmental Engineering→Air Pollution

Q27

MCQ[2 Marks]

Emission standard for HCl (at 11% $O_2$) is $50\text{ mg/Nm}^3$. Measured HCl is $42\text{ mg/Nm}^3$ at 13% $O_2$. Assuming 21% air oxygen, the CORRECT statement is:

(A)

No compliance, as corrected HCl emission is greater than standard

(B)

Compliance is there, corrected HCl emission is lesser

(C)

Compliance is there, no need to correction since O2 > 11%

(D)

No compliance, as O2 is greater than 11%

Explanation

GATE→2023→Environmental Engineering→Air Pollution

Q28

MCQ[1 Mark]

Which one of the following statements is TRUE for Greenhouse Gas (GHG) in the atmosphere?

(A)

Absorbs incoming short wavelength solar radiation, allows outgoing long wavelength

(B)

Allows incoming long wavelength, absorbs short wavelength

(C)

Allows both incoming long wavelength and outgoing short wavelength

(D)

Allows incoming short wavelength solar radiation, absorbs long wavelength radiation from earth

Explanation

GATE→2023→Environmental Engineering→Air Pollution

Q29

MSQ[2 Marks]

Which of the following statements is/are TRUE in relation to the Maximum Mixing Depth (or Height) $D_{\max}$ in the atmosphere?

(A)

D_max is always equal to height of unstable air layer

(B)

Ventilation coefficient depends on D_max

(C)

Smaller D_max will have smaller air pollution potential if meteorological conditions remain same

(D)

Vertical dispersion of pollutants occurs up to D_max

Explanation

Municipal Solid Wastes

4 Questions

GATE→2025→Environmental Engineering→Municipal Solid Wastes

Q30

MSQ[2 Marks]

Organic fraction of MSW mixed with municipal sludge. Which of the following options is/are true:

(A)

0.33 kg of sludge added per kg of OFMSW

(B)

Density of mixture is 365 kg/m^3

(C)

0.66 kg of sludge added per kg of OFMSW

(D)

Density of mixture is 450 kg/m^3

Explanation

GATE→2024→Environmental Engineering→Municipal Solid Wastes

Q31

MCQ[1 Mark]

Match MSW components (P: Ferrous metals, Q: Aluminum/copper, R: Glass/ceramics, S: Food waste) with treatment/separation techniques.

(A)

P-iv, Q-iii, R-i, S-ii

(B)

P-iv, Q-iii, R-ii, S-i

(C)

P-iii, Q-iv, R-ii, S-i

(D)

P-iv, Q-iii, R-i, S-ii

Explanation

GATE→2023→Environmental Engineering→Municipal Solid Wastes

Q32

MSQ[1 Mark]

Which of the following statements is/are TRUE for Refuse-Derived Fuel (RDF) in Municipal Solid Waste management?

(A)

HHV of unprocessed MSW is higher than HHV of RDF

(B)

RDF can be made in powdered form

(C)

Inorganic fraction of MSW is mostly converted to RDF

(D)

RDF cannot be used in conjunction with oil

Explanation

GATE→2023→Environmental Engineering→Municipal Solid Wastes

Q33

NAT[2 Marks]

Solid waste composition table given with as-discarded energy contents. If moisture content is 26%, energy content on dry-weight basis (in MJ/kg) is

Explanation