GATE CE Water and Waste Water Quality and Treatment PYQs & Answers — Page 4

Questions 31–40 of 81. Imported answers require independent review unless marked reviewed.

The theoretical aerobic oxidation of biomass (C

N) is given below:

N + 5O

→ 5CO

+ NH

+ 2H

The biochemical oxidation of biomass is assumed as a first-order reaction with a rate constant of 0.23/d at 20°C (logarithm to base e). Neglecting the second-stage oxygen demand from its biochemical oxidation, the ratio of BOD

at 20°C to total organic carbon (TOC) of biomass is __________ (round off to two decimal places).

[Consider the atomic weights of C, H, O and N as 12 g/mol, 1 g/mol, 16 g/mol and 14 g/mol, respectively]

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The total hardness in raw water is 500 milligram per liter as CaCO₃. The total hardness of this raw water, expressed in milligram equivalent per liter, is

(Consider the atomic weights of Ca, C, and O as 40 g/mol, 12 g/mol, and 16 g/mol, respectively.)

Your answerChoose one option.

100

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For wastewater coming from a wood pulping industry, Chemical Oxygen Demand (COD) and 5-day Biochemical Oxygen Demand (BOD₅) were determined. For this wastewater, which of the following statement(s) is/are correct?

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

COD > BOD₅

COD ≠ BOD₅

COD < BOD₅

COD = BOD₅

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

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

Microfiltration

Electrodialysis

Ultrafiltration

Reverse osmosis

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Henry’s law constant for transferring O₂ from air into water, at room temperature, is 1.3

. Given that the partial pressure of O₂ in the atmosphere is 0.21 atm, the concentration of dissolved oxygen (mg/liter) in water in equilibrium with the atmosphere at room temperature is

(Consider the molecular weight of O₂ as 32 g/mol)

Your answerChoose one option.

8.7

0.8

198.1

0.2

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A 100 mg of HNO

(strong acid) is added to water, bringing the final volume to 1.0 liter. Consider the atomic weights of H, N, and O, as 1 g/mol, 14 g/mol, and 16 g/mol, respectively. The final pH of this water is (Ignore the dissociation of water.)

Your answerChoose one option.

2.8

6.5

3.8

8.5

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In a water sample, the concentrations of Ca

, Mg

and HCO

are 100 mg/L, 36 mg/L and 122 mg/L, respectively. The atomic masses of various elements are: Ca = 40, Mg = 24, H = 1, C = 12, O = 16.

The total hardness and the temporary hardness in the water sample (in mg/L as CaCO

) will be

Your answerChoose one option.

400 and 100, respectively.

400 and 300, respectively.

500 and 100, respectively.

800 and 200, respectively.

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A wastewater sample contains two nitrogen species, namely ammonia and nitrate. Consider the atomic weight of N, H, and O as 14 g/mol, 1 g/mol, and 16 g/mol, respectively. In this wastewater, the concentration of ammonia is 34 mg NH₃/liter and that of nitrate is 6.2 mg NO₃⁻/liter. The total nitrogen concentration in this wastewater is ______ milligram nitrogen per liter. (round off to one decimal place)

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A 2 % sewage sample (in distilled water) was incubated for 3 days at 27 °C temperature. After incubation, a dissolved oxygen depletion of 10 mg/L was recorded. The biochemical oxygen demand (BOD) rate constant at 27 °C was found to be 0.23 day⁻¹ (at base e).

The ultimate BOD (in mg/L) of the sewage will be____________. (round off to the nearest integer)

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A water treatment plant has a sedimentation basin of depth 3 m, width 5 m, and length 40 m. The water inflow rate is 500 m³/h. The removal fraction of particles having a settling velocity of 1.0 m/h is ________. (round off to one decimal place)

(Consider the particle density as 2650 kg/m³ and liquid density as 991 kg/m³)

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GATE CE Water and Waste Water Quality and Treatment PYQs

Question 64

Question 22

Question 26

Question 27

Question 42

Question 42

Question 43

Question 59

Question 60

Question 61