GATE CE topic:water-and-wastewater-treatment PYQs & Answers — Page 5

Questions 41–50 of 81. Imported answers require independent review unless marked reviewed.

Which one of the following is correct?

Your answerChoose one option.

The partially treated effluent from a food processing industry, containing high concentration of biodegradable organics, is being discharged into a flowing river at a point P. If the rate of degradation of the organics is higher than the rate of aeration, then dissolved oxygen of the river water will be lowest at point P.

The most important type of species involved in the degradation of organic matter in the case of activated sludge process based wastewater treatment is chemoheterotrophs.

For an effluent sample of a sewage treatment plant, the ratio BOD₅-day,20°C upon ultimate BOD is more than 1.

A young lake characterized by low nutrient content and low plant productivity is called eutrophic lake.

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

The hardness of a water sample is measured directly by titration with 0.01 M solution of ethylenediamine tetraacetic acid (EDTA) using eriochrome black T (EBT) as an indicator. The EBT reacts and forms complexes with divalent metal cations present in the water. During titration, the EDTA replaces the EBT in the complex. When the replacement of EBT is complete at the end point of the titration, the colour of the solution changes from

Your answerChoose one option.

blue-green to reddish brown

blue to colourless

reddish brown to pinkish yellow

wine red to blue

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

A 50 mL sample of industrial wastewater is taken into a silica crucible. The empty weight of the crucible is 54.352 g. The crucible with the sample is dried in a hot air oven at 104 °C till a constant weight of 55.129 g. Thereafter, the crucible with the dried sample is fired at 600 °C for 1 h in a muffle furnace, and the weight of the crucible along with residue is determined as 54.783 g. The concentration of total volatile solids is ______.

Your answerChoose one option.

1540 μg/L

8620 mg/L

6920 mg/L

1700 mg/L

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

A water sample is analyzed for coliform organisms by the multiple-tube fermentation method. The results of confirmed test are as follows:

Sample size (mL)	Number of positive results out of 5 tubes	Number of negative results out of 5 tubes
0.01	5	0
0.001	3	2
0.0001	1	4

The most probable number (MPN) of coliform organisms for the above results is to be obtained using the following MPN Index.

Combination of positive tubes	MPN Index per 100 mL
0 – 2 – 4	11
1 – 3 – 5	19
4 – 2 – 0	22
5 – 3 – 1	110

The MPN of coliform organisms per 100 mL is

Your answerChoose one option.

110000

11000

1100

110

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

A water filtration unit is made of uniform-size sand particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is

Your answerChoose one option.

m/s

0.69 cm/s

0.75 cm/s

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

Ammonia nitrogen is present in a given wastewater sample as the ammonium ion (NH₄⁺) and ammonia (NH₃). If pH is the only deciding factor for the proportion of these two constituents, which of the following is a correct statement?

Your answerChoose one option.

At pH above 9.25, only NH₄⁺ will be present.

At pH below 9.25, NH₃ will be predominant.

At pH 7.0, NH₄⁺ and NH₃ will be found in equal measures.

At pH 7.0, NH₄⁺ will be predominant.

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

An activated sludge process (ASP) is designed for secondary treatment of 750 m³/day of municipal wastewater. After primary clarifier, the ultimate BOD of the influent, which enters into ASP reactor is 200 mg/L. Treated effluent after secondary clarifier is required to have an ultimate BOD of 20 mg/L. Mix liquor volatile suspended solids (MLVSS) concentration in the reactor and the underflow is maintained as 3000 mg/L and 12000 mg/L, respectively. The hydraulic retention time and mean cell residence time are 0.2 day and 10 days, respectively. A representative flow diagram of the ASP is shown below. The underflow volume (in m³/day, round off to one decimal place) of sludge wastage is ________.

Diagram for Civil Engineering question 51

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

A secondary clarifier handles a total flow of 9600 m³/d from the aeration tank of a conventional activated-sludge treatment system. The concentration of solids in the flow from the aeration tank is 3000 mg/L. The clarifier is required to thicken the solids to 1200 mg/L, and hence it is to be designed for a solid flux of 3.2 kg/m².h. The surface area of the designed clarifier for thickening (in m², in integer) is ________.

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

A grit chamber of rectangular cross-section is to be designed to remove particles with diameter of 0.25 mm and specific gravity of 2.70. The terminal settling velocity of the particles is estimated as 2.5 cm/s. The chamber is having a width of 0.50 m and has to carry a peak wastewater flow of 9720 m³/d giving the depth of flow as 0.75 m. If a flow-through velocity of 0.3 m/s has to be maintained using a proportional weir at the outlet end of the chamber, the minimum length of the chamber (in m, in integer) to remove 0.25 mm particles completely is ________.

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

During chlorination process, aqueous (aq) chlorine reacts rapidly with water to form Cl⁻, HOCl, and H⁺ as shown below

Cl₂ (aq) + H₂O ⇌ HOCl + Cl⁻ + H⁺

The most active disinfectant in the chlorination process from amongst the following, is

Your answerChoose one option.

H⁺

HOCl

Cl⁻

H₂O

You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answer

GATE CE topic:water-and-wastewater-treatment PYQs

Question 12

Question 15

Question 28

Question 33

Question 33

Question 34

Question 51

Question 52

Question 52

Question 16