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Water and Wastewater Quality Parameters & River Pollution(9)Water Treatment Methods & Distribution(9)Sewage Treatment, Sludge & Wastewater Management(7)Kinetics and Reactor Design(6)

Water and Wastewater Quality Parameters & River Pollution

9 Questions

GATE→2026→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q1

MSQ[1 Mark]

Which of the following options is/are CORRECTLY listing the species included in Total Kjeldahl Nitrogen (TKN) estimation of an aqueous sample?

(A)

Ammoniacal - N

(B)

Nitrite - N

(C)

Nitrate - N

(D)

Organic - N

Explanation

GATE→2026→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q2

MCQ[2 Marks]

The analysis of a water sample is shown in the table. The hardness of the water sample is _____ mg/L as $CaCO_3$. Atomic weight (g/mol): $Ca=40$, $Mg=24$, $Na=23$, $Cl=35.5$, $S=32$, $O=16$, $N=14$. Species Concentration (mg/L): $Na^+ = 30$, $Ca^{2+} = 10$, $Mg^{2+} = 15$, $Cl^- = 30$, $SO_4^{2-} = 60$, $NO_3^- = 5$.

(A)

87.5

(B)

62.5

(C)

25.5

(D)

47.5

Explanation

GATE→2026→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q3

NAT[2 Marks]

The calibration graph between absorbance and the concentration of chromate ($CrO_4^{2-}$) in a water sample is given by the equation $y = 0.8003x + 0.0055$. For an absorbance of $0.35$ in a water sample, the estimated $Cr(VI)$ concentration is _____ mg/L (rounded off to two decimal places). (Atomic weights: $Cr = 52$, $O = 16$)

Explanation

GATE→2024→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q4

MSQ[2 Marks]

The Streeter-Phelp's oxygen sag equation for a river is based on a few assumptions. The correct assumption(s) is/are

(A)

At any instant the deoxygenation rate is directly proportional to the amount of oxidizable organic material present.

(B)

At any instant the deoxygenation rate is inversely proportional to the amount of oxidizable organic material present.

(C)

The reoxygenation rate is directly proportional to the dissolved oxygen deficit.

(D)

The reoxygenation rate and deoxygenation rate are directly proportional to the saturation concentration of dissolved oxygen.

Explanation

GATE→2024→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q5

NAT[2 Marks]

An industry discharges $2\text{ MLD}$ of wastewater with a temperature of $45^\circ\text{C}$ and a pH of $2$, whereas the neighboring industry produces $3\text{ MLD}$ of wastewater with a temperature of $30^\circ\text{C}$ and pH of $8$. If both the wastewaters are mixed and carried, the resulting pH is _____ (rounded off to 2 decimal places). (Neglect buffering capacity and temperature effect on pH)

Explanation

GATE→2023→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q6

MCQ[1 Mark]

For testing alkalinity for a water sample, first phenolphthalein indicator is added. The water remains colorless. However, when a few drops of methyl orange is added to the sample, the color turns yellow. As per these observations, the correct choice is

(A)

Absence of $CO_3^{2-}$ and/or $HCO_3^-$ but the presence of $OH^-$ ions in the sample

(B)

Presence of $CO_3^{2-}$ and/or $HCO_3^-$ but the absence of $OH^-$ ions in the sample

(C)

Absence of $CO_3^{2-}$, $HCO_3^-$ and $OH^-$ ions in the sample

(D)

Presence of $CO_3^{2-}$, $HCO_3^-$ and $OH^-$ ions in the sample

Explanation

GATE→2023→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q7

NAT[2 Marks]

You are doing an experiment to find out $BOD_5$ of a wastewater. You have taken $25\text{ mL}$ wastewater having ultimate BOD of $75\text{ mg/L}$ and placed it in $300\text{ mL}$ BOD bottle and filled it with dilution water. The initial DO of the diluted sample is $6.5\text{ mg/L}$. On the $7^{\text{th}}$ day, the DO is found to be $1.25\text{ mg/L}$. The $BOD_5$ of the wastewater sample is _____ (in mg/L, rounded off to two decimal places).

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q8

MCQ[1 Mark]

Specific conductance is used in water analysis to indirectly estimate dissolved solids. The measurements used in the method accounts for

(A)

Cations only

(B)

All ions

(C)

Anions only

(D)

Un-ionized species

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Water and Wastewater Quality Parameters & River Pollution

Q9

MSQ[2 Marks]

Average values of the re-aeration rate constant for river X and river Y are $0.92\text{ per day}$ and $1.12\text{ per day}$, respectively. Average de-oxygenation rate constants for the same rivers are $0.23\text{ per day}$ and $0.35\text{ per day}$ respectively. Then, which of the following statement(s) is/are correct?

(A)

Self-purification capacity of river Y is more than that of river X.

(B)

Self-purification capacity of river X is more than that of river Y.

(C)

River Y has higher turbulence and/or higher velocity and/or higher algal growth compared to river X.

(D)

Pollutants in river X are more biodegradable than that in river Y.

Explanation

Water Treatment Methods & Distribution

9 Questions

GATE→2026→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q10

MSQ[2 Marks]

Which of the following options is/are TRUE about reverse osmosis process?

(A)

Reverse osmosis is used as a pretreatment for microfiltration process.

(B)

Ultrafiltration is used as a pretreatment for reverse osmosis process.

(C)

Membrane fouling occurs in microfiltration and reverse osmosis processes.

(D)

Concentration polarization does not occur in reverse osmosis process.

Explanation

GATE→2026→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q11

MSQ[2 Marks]

Which of the following options is/are TRUE about coagulation-flocculation process?

(A)

Collision of colloidal particles due to their Brownian motion results in orthokinetic flocculation.

(B)

Collision of colloidal particles due to the external mixing of bulk medium results only in perikinetic flocculation.

(C)

In an electric double layer model of a colloidal particle, Stern layer is more compact than the diffuse layer.

(D)

The zeta potential is also called Stern potential.

Explanation

GATE→2024→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q12

MCQ[1 Mark]

The processes of removal of particles in a rapid sand filter with their description is given in the table. - (i) Straining -> P: Removes only particles large enough to get caught in pores - (ii) Sedimentation -> Q: Larger/heavier particles settle on sand grain - (iii) Interception -> R: Particles following streamline but too large caught by brushing against sand - (iv) Diffusion -> S: Very small particles experiencing Brownian motion Select the correct match.

(A)

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

(B)

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

(C)

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

(D)

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

Explanation

GATE→2024→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q13

MSQ[1 Mark]

With respect to particle settling in wastewater treatment systems; the correct statement(s) is/are

(A)

Settling in grit chamber and primary sedimentation tanks are examples of Type-I settling

(B)

Settling in primary sedimentation tank and secondary sedimentation tank are examples of Type-II settling

(C)

Settling in grit chamber is an example of Type-I settling, whereas settling in primary sedimentation tank is an example of Type-II settling

(D)

Settling in secondary sedimentation tank is an example of Type-III settling, whereas settling in primary sedimentation tank is an example of Type-II settling

Explanation

GATE→2023→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q14

NAT[1 Mark]

River water containing two types of spherical suspended particles (clay particles, metal particles) is retained in a sedimentation tank. The clay particles having diameter of $75\text{ }\mu\text{m}$ and specific gravity of $2.65$ is settling in the tank with a constant velocity. The velocity of clay particles is 2 times of that of metal particles having specific gravity of $8$. Assume discrete settling and laminar flow conditions within the sedimentation tank. The estimated diameter of the metal particles is _____ (in $\mu\text{m}$ rounded off to integer).

Explanation

GATE→2023→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q15

NAT[2 Marks]

A flask ($100\text{ ml}$ volume) has wastewater, which has $0.12\text{ mg/L}$ geosmin. Activated carbon is added in this flask for adsorbing geosmin as per the Freundlich isotherm model ($Q = 2.6 \times C^{0.73}$ where $Q$ is mg adsorbate/mg adsorbent and $C$ is the equilibrium concentration in $\text{mg/L}$). Activated carbon to be added in this flask for getting final remaining geosmin concentration of $0.05\text{ mg/L}$ would be _____ (in mg/L rounded off to three decimal places).

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q16

MCQ[1 Mark]

A river water sample has pH of 4 and suspended solids concentration of $100\text{ mg/L}$. If, alum is chosen as a coagulant, what will be the coagulation mechanism?

(A)

Ionic layer compression only

(B)

Sweep coagulation and Polymer bridging

(C)

Polymer bridging only

(D)

Charge neutralization, surface adsorption, ionic layer compression

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q17

NAT[2 Marks]

Clean water is passed through a bed of uniform spherical sand at a filtration velocity of $0.002\text{ m/sec}$. The sand grains are $0.4\text{ mm}$ in diameter and have a specific gravity of $2.65$. Bed depth is $0.67\text{ m}$ and porosity ($\eta$) is $0.35$. Given: water density $= 998.2\text{ kg/m}^3$; water dynamic viscosity $= 1.002 \times 10^{-3}\text{ Pa}\cdot\text{s}$. Friction factor ($f$) is given as: $f = 1.75 + \{150 \times (1 - \eta) / Re\}$. The headloss (in m, rounded off to three decimal places) calculated using the Carmen-Kozney equation is

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Water Treatment Methods & Distribution

Q18

NAT[2 Marks]

A centrifuge is processing $1000\text{ litres per hour}$ of water containing $2\text{ g per litre}$ of suspended solids. The thickened slurry coming out of the centrifuge has solids concentration of $20\text{ g per 100 ml}$. If the centrifuge has $99\%$ efficiency based on solids separation, the flow rate (in litres per hour, rounded off to one decimal place) of the supernatant stream will be

Explanation

Sewage Treatment, Sludge & Wastewater Management

7 Questions

GATE→2026→Water & Wastewater Treatment and Management→Sewage Treatment, Sludge & Wastewater Management

Q19

MCQ[1 Mark]

Which ONE of the following options CORRECTLY matches the processes associated with the growth condition given in the table?

(A)

(P) - (ii); (Q) - (iii); (R) - (iv); (S) - (i)

(B)

(P) - (iii); (Q) - (ii); (R) - (iv); (S) - (i)

(C)

(P) - (iii); (Q) - (i); (R) - (iv); (S) - (ii)

(D)

(P) - (iv); (Q) - (iii); (R) - (ii); (S) - (i)

Explanation

GATE→2026→Water & Wastewater Treatment and Management→Sewage Treatment, Sludge & Wastewater Management

Q20

MSQ[1 Mark]

Which of the following processes is/are primarily used to remove the organic matter in sludge?

(A)

Digestion

(B)

Incineration

(C)

Magnetic separation

(D)

Wet-oxidation

Explanation

GATE→2026→Water & Wastewater Treatment and Management→Sewage Treatment, Sludge & Wastewater Management

Q21

NAT[2 Marks]

A sewage treatment plant employing activated sludge process is operated under the following conditions: - Wastewater flow rate ($Q$) = $0.150\text{ m}^3/\text{s}$ - Soluble $BOD_5$ in influent ($S_0$) = $84\text{ mg/L}$ - Soluble $BOD_5$ in effluent ($S$) = $11\text{ mg/L}$ - Mean cell residence time ($\theta_c$) = $5\text{ days}$ - Total yield coefficient ($Y$) = $0.5\text{ kg MLVSS/kg } BOD_5$ removed - Decay rate ($k_d$) = $0.050\text{ day}^{-1}$ The net waste activated sludge produced in the plant is _____ $\text{kg VSS/day}$ (rounded off to two decimal places).

Explanation

GATE→2024→Water & Wastewater Treatment and Management→Sewage Treatment, Sludge & Wastewater Management

Q22

MCQ[1 Mark]

Crown corrosion of reinforced cement concrete sewer is caused by

(A)

sulfur oxidizing bacteria

(B)

iron oxidizing bacteria

(C)

denitrifying bacteria

(D)

fermentative bacteria

Explanation

GATE→2024→Water & Wastewater Treatment and Management→Sewage Treatment, Sludge & Wastewater Management

Q23

NAT[2 Marks]

One million liters per day (MLD) of wastewater with a soluble BOD of $200\text{ mg/L}$ is treated in an activated sludge process. The BOD of treated wastewater is $20\text{ mg/L}$. The observed yield coefficient of the biological system is $0.35$. The daily biomass generation in the system is _____ kg (an integer value).

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Sewage Treatment, Sludge & Wastewater Management

Q24

MSQ[1 Mark]

For effluents generated by a molasses based distillery and wood based pulp and paper industry, which of the following statement(s) is/are NOT correct?

(A)

Both the effluents have dark colour.

(B)

Both the effluents have high toxicity.

(C)

Both the effluents generally have BOD greater than 15,000 ppm.

(D)

Both the effluents have high pH.

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Sewage Treatment, Sludge & Wastewater Management

Q25

NAT[2 Marks]

A sewage treatment plant with a capacity of $10\text{ million litres per day (MLD)}$ is treating the sewage through an aerobic biological process. The inlet and outlet BOD are measured as $100$ and $30\text{ mg/l}$, respectively. If the mixed microbial culture has an observed biomass yield of $0.5\text{ g Volatile Suspended Solids (VSS)/g BOD}$, the sludge production rate (in kg per day, rounded off to one decimal place) when the plant is operating at $80\%$ capacity is

Explanation

Kinetics and Reactor Design

6 Questions

GATE→2026→Water & Wastewater Treatment and Management→Kinetics and Reactor Design

Q26

NAT[2 Marks]

Reaction $A \rightarrow B$ follows first-order elementary kinetics and the reaction rate constant for A is $0.01\text{ min}^{-1}$. The time taken to reduce the concentration of A from $100\text{ M}$ to $10\text{ M}$ in a batch reactor is _____ min (rounded off to one decimal place).

Explanation

GATE→2026→Water & Wastewater Treatment and Management→Kinetics and Reactor Design

Q27

NAT[2 Marks]

A continuous flow stirred tank reactor (CSTR) operates under a steady-state condition with a flow rate of $Q = 300\text{ L/hour}$. The influent concentration of a substrate entering the reactor is $S_0 = 150\text{ mg/L}$. To give a treatment efficiency of $76\%$ for the substrate that decays according to half-order kinetics with a rate constant $k = 0.05\text{ (mg/L)}^{1/2}\text{ hr}^{-1}$, the required volume of the reactor is _____ $\text{m}^3$ (answer in integer).

Explanation

GATE→2024→Water & Wastewater Treatment and Management→Kinetics and Reactor Design

Q28

MCQ[2 Marks]

Consider second order kinetics ($r_c = -kC^2$) under steady state condition. The ratio of volume of a complete mixed reactor (CMR) to that of a plug flow reactor (PFR) to achieve $90\%$ reduction in the concentration is (Inlet concentrations in both the reactors are same).

(A)

10.0

(B)

1.0

(C)

0.1

(D)

2.3

Explanation

GATE→2023→Water & Wastewater Treatment and Management→Kinetics and Reactor Design

Q29

NAT[2 Marks]

An aeration tank needs to be installed for the removal of VOC from water, where the required rate of flow of water through the aeration tank is $180,000\text{ m}^3/\text{d}$. Permissible limit of VOC in the water is $12\text{ }\mu\text{g/L}$. The saturation concentration of VOC is $5\text{ }\mu\text{g/L}$ and gas transfer rate constant is $0.40\text{ per second}$ at $25^\circ\text{C}$. The initial concentration of VOC in the water is $33\text{ }\mu\text{g/L}$. The volume of the aeration tank to satisfy the permissible limit of VOC at $25^\circ\text{C}$ is _____ (in $\text{m}^3$, rounded off to two decimal places).

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Kinetics and Reactor Design

Q30

MCQ[2 Marks]

Which one of the following statements is NOT correct with respect to a batch reactor?

(A)

No reactant is added after the reactor has started operation.

(B)

No product is withdrawn during the course of the reactor operation.

(C)

The reactor operates under steady state.

(D)

The reactor operation is carried out for a pre-specified duration.

Explanation

GATE→2022→Water & Wastewater Treatment and Management→Kinetics and Reactor Design

Q31

MSQ[2 Marks]

Which of the following statement(s) is/are NOT correct while comparing continuously stirred tank reactor (CSTR) and plug flow reactor (PFR)?

(A)

CSTR and PFR are normally operated under steady state condition.

(B)

There is complete homogeneity in the CSTR while there are concentration variations within the PFR.

(C)

The overall reaction carried out in a PFR is always higher than that in a CSTR for same total volume.

(D)

Reaction kinetics do not play any role in choosing between CSTR and PFR.

Explanation