# NPTEL Wastewater Treatment And Recycling Week 4 Assignment Answer 2023

NPTEL Wastewater Treatment And Recycling Week 4 Assignment Solutions

## NPTEL Wastewater Treatment And Recycling Week 4 Assignment Answer 2023

1. Self-purification processes in rivers, refers to:

a. Installing in-situ sediment filters for contaminant removal in rivers
b. Setting up in-stream natural-processes based treatment systems in rivers
c. Dosing chemicals to the rivers which leads to precipitate and remove
pollutants
d. Naturally-occurring processes in rivers which reduces the pollutant levels in river water

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2. Match the type of processes for contaminant fate and transport given in first column with the specific process given in second column:

Type of process

(i) Mass Transport
(ii) Phase Transfer
(iii Transformation

Contaminant Fate and Transport Processes
B. Dispersion
C. Volatilization

a. (i)-B, (ii)-A.(iii)-C
b. (i)-B. (ii)-C. (iii)-A
c. (i)-C, (in)-A. (ill)-B
d. (1)-A. (in)-C. (il)-B

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3. After the point of discharge of a wastewater stream, the first zone to appear in a river is:

a. Decomposition Zone
b. Septic Zone
c. Recovery Zone
d. Reaeration Zone

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4. For a river receiving wastewater discharge, the most critical stretch is considered, where:

a. DO is minimum
b. DO is maximum
c. BOD is minimum
d. BOD is maximum

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5. The Streeter Phelps Equation is used to describes the variation of DO in a stream receiving wastewater discharge. Which of the following assumptions is correct about the classical Streeter Phelps Equation?

a. The flow pattern in the river follows plug-flow
b. Only re-aeration is taken as the source of DO in the river water
c. Only carbonaceous BOD is considered responsible for DO consumption
d. All of the above

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6. Identify the correct statements regarding conservative pollutants:
Statement I
: Conservative pollutants are non-degradable, thus stable and persistent in nature.
Statement II: Since conservative pollutants are not degraded in nature, it poses lesser environmental risk than non-conservative pollutants.

a. Statement I is correct. while statement II is incorrect
b. Statement II is correct. while statement I is incorrect
c. Both. statements I and II are correct
d. Both. statements I and II are incorrect

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7. Consider the following generic mass balance equation (in usual notations):

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8. For mass balance equation in a Continuous Stirred Tank Reactor (CSIR):

a. Inflow and outflow flux is considered as zero
b. Reaction term in the mass balance equation is considered as zero
c. The outflow concentration of contaminant is taken same as the concentration
in the reactor
d. All of the above

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9. If the reaction kinetics in a mass balance equation is expressed as dCIdt = k.C”, the order of the reaction is:

a. First order
b. nt order
c. Ct order
d. It order

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10. Mixing or no-mixing in a reactor guides in identifying:

a. Conservative or reactive nature of pollutant
c. Batch or continuous flow process
d. Plug flow conditions in the reactor

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11. A plug-flow reactor of volume 250 m’ is operating under steady state at 16 m°h flow of a wastewater stream having influent BODs as 360 mg/L. If the BOD decay rate constant is 0.141 per hour, the outlet BOD Concentration would be:

a. 20 mg/L
b. 40 mg/L
c. 80 mg L
d. 160 mg/I

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12. A mixed tank reactor is to be designed for treating phenol in an industrial wastewater, form an initial concentration of 70 mg/L to a final outlet concentration of 5 mg/L, where phenol is expected to undergo first order decay at a rate constant of 0.65/d. If the reactor is to be operated at steady state, the design volume of reactor for treating 20 kL/d wastewater would be:

а. 135 m3
b. 294 m3
с. 400 m°
d. 620 m

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Question Statement (13-15): The 5-day BOD of a wastewater sample measured at 20°C incubation temperature was found to be 320 mg/L. The laboratory data revealed that the BOD reaction rate constant (at 20°C) k2o (base e) was 0.26/day, and the temperature coefficient was 1.035. Based on the information. answer the following questions:

13) The ultimate BOD of wastewater, at 20°C incubation temperature, is (in mg/L)

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14. The 3-day BOD of this wastewater, at 20°C incubation temperature, is (in mg/L)

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15. The 3-day BOD of this wastewater. at 27°C incubation temperature. is (in mg L):

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