Environmental Studies · Chemistry

Water and Wastewater Treatment

1,345 Questions

This topic deals with water purification, wastewater treatment methods, and industrial effluent management. It includes questions on filtration, disinfection, and water hardness removal. These concepts are tested in environmental science and engineering exams.

Water purificationWastewater treatmentBioremediation strategiesWater hardness removalIndustrial effluent management

Water and Wastewater Treatment Questions

Multiple choice

A flocculating agent is added to a dispersion of solids in a liquid for the formation of flocs. Which among the following is used as a flocculating agent in the purification of drinking water ?

  1. Aluminium phosphate

  2. Aluminium phosphide (AlP)

  3. Aluminium selenide

  4. Aluminium sulphate
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Aluminium sulphate, is a chemical compound with the formula Al2(SO4)3. Aluminium sulphate is mainly used as a flocculating agent in the purification of drinking water and waste water treatment plants, and also in paper manufacturing.

Multiple choice

Which of the following substances can also be employed as anti-fouling agents or disinfectants?

  1. Spermicide

  2. Biocide

  3. Fungicides

  4. Acaricides
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A biocide is a chemical substance or microorganism which can deter, render harmless or exert a controlling effect on any harmful organism by chemical or biological means. Biocides are commonly used in medicine, agriculture, forestry, and industry. Biocidal substances and products are also employed as anti-fouling agents or disinfectants under other circumstances.

Multiple choice

Microbial fuel cells are considered a source of sustainable energy. Why?

  1. They use living organisms ass catalysts to generate electricity from certain substrates.
  2. They use a variety of inorganic materials as substrates.
  3. They can be installed in waste water treatment plants to cleanse water and produce electricity.

Which of the statements given above is/ are correct?

  1. 1 only

  2. 2 and 3 only

  3. 1 and 3 only

  4. 1, 2 and 3
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A microbial fuel cell is a device that converts chemical energy to electrical energy by the catalytic reaction of microorganisms. Among the electrochemically active bacteria are Shewanella putrefaciens, Aeromonas hydrophila. Mediator-less microbial fuel cells can, besides running on wastewater, also derive energy directly from certain aquatic plants. Virtually any organic material could be used to feed the fuel cell, including coupling cells to wastewater treatment plants.

Multiple choice

Consider the following unit processes commonly used in water treatment: rapid mixing (RM), flocculation (F), primary sedimentation (PS), secondary sedimentation (SS), chlorination (C) and rapid sand filtration (RSF). The order of these unit processes (from first to last) in a conventional water treatment plant is
  1. PS$\rightarrow$RSF$\rightarrow$F$\rightarrow$RM$\rightarrow$SS$\rightarrow$C
  2. PS$\rightarrow$F$\rightarrow$RM$\rightarrow$RSF$\rightarrow$SS$\rightarrow$C
  3. PS$\rightarrow$F$\rightarrow$SS$\rightarrow$RSF$\rightarrow$RM$\rightarrow$C
  4. PS$\rightarrow$RM$\rightarrow$F$\rightarrow$SS$\rightarrow$RSF$\rightarrow$C
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

 $\text{Order of treatment is}\\ PS \rightarrow RM \rightarrow F \rightarrow SS \rightarrow RSF \rightarrow C \\ \text{Rapid mixing is the process by which coagulant is throughly mixed with raw water for effective flocculation.}$

Multiple choice

A completely mixed activated sludge process is used to treat a wastewater flow of 1 million litres per day (1 MLD) having a BOD5 of 200 mgIL. The biomass concentration in the aeration tank is 2000 mg/L and the concentration of the net biomass leaving the system of 5 mgIL. The aeration tank has a volume of 200 m3.

What is the hydraulic retention time of the wastewater in aeration tank?

  1. 0.2 h

  2. 4.8 h

  3. 10 h

  4. 24 h
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 

Multiple choice

A plain sedimentation tank with a length of 20 m, width of 10 m and a depth of 3 m is used in a water treatment plant to treat 4 million litres of water per day (4 MLD). The average temperature of water is 20°C. The dynamic viscosity of water is 1.002 x 10–3 N.s/m2 at 20°C. Density of water is 998.2 kg/M3. Average specific gravity of particles is 2.65.

What is the surface overflow rate in the sedimentation tank?

  1. 20 m3/ m2/ day

  2. 40 m3/ m2/ day

  3. 67 m3/ m2/ day

  4. 133 m3/ m2/ day
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 $\text{Surface overflow rate} = \frac{Q}{Area of the tank}\\ = \frac{4 \times 10^6 \times 10^{-3}}{20 \times 10}m^3/day = 20 m^3 / m^2 / day$