Test 23 - Grit Chamber Principles and Design

Question 1 ప్రశ్న 1

What is the principal treatment objective of a grit chamber in a municipal sewage treatment plant?

A To separate relatively heavy inorganic particles such as sand and grit while limiting deposition of lighter organic solids. B To disinfect incoming sewage before biological treatment. C To remove most dissolved biodegradable organic matter by microbial oxidation. D To remove dissolved nitrogen and phosphorus by chemical precipitation.

Question 2 ప్రశ్న 2

Which conventional sequence most appropriately places a grit chamber within a sewage treatment plant?

A Biological reactor, grit chamber, coarse screen, primary clarifier. B Screening, grit removal, primary sedimentation, biological treatment. C Primary sedimentation, disinfection, grit removal, screening. D Final clarifier, screening, grit removal, sewage inlet.

Question 3 ప్రశ్న 3

For a conventional grit-chamber design reference, which target particle characteristics are commonly assumed, while recognizing that actual requirements can differ?

A Nominal grit size around 0.20 mm and particle specific gravity around 2.65. B Nominal grit size 20 mm and particle specific gravity 1.00. C Nominal grit size 0.002 mm and particle specific gravity 1.01. D All grit particles must have identical dimensions and particle specific gravity of 1.20.

Question 4 ప్రశ్న 4

A velocity-controlled horizontal-flow grit chamber is operated near a longitudinal mean velocity of 0.30 m/s. What is the principal reason for selecting a moderate, controlled velocity?

A To make both mineral grit and putrescible organic particles settle as rapidly as possible. B To keep every particle suspended and avoid all deposits. C To produce sufficient pressure for membrane filtration downstream. D To encourage dense grit settling while carrying much of the lighter organic material through the chamber.

Question 5 ప్రశ్న 5

Which outcome is most likely when horizontal flow velocity deviates substantially from its suitable operating range in a conventional grit channel?

A Low velocity increases grit carryover, while very high velocity increases organic deposition. B Both very low and very high velocities always improve grit-organic separation. C Too low a velocity may increase organic deposition, while too high a velocity may increase grit carryover or scour. D The separation of organic and inorganic particles is independent of longitudinal velocity.

Question 6 ప్రశ్న 6

Which pairing correctly describes aerated and vortex-type grit chambers?

A Aerated chambers use only chemical coagulation; vortex chambers rely only on bar screening. B Aerated chambers use helical flow induced by side air injection; vortex chambers commonly use tangential inlet flow and a grit hopper. C Aerated chambers are always pressurised; vortex chambers have no liquid motion. D Both arrangements require a long straight channel controlled by a proportional weir as their defining separation mechanism.

Question 7 ప్రశ్న 7

A rectangular grit channel carries 0.18 m^3/s through a 0.90 m water width and a 0.80 m flowing depth. What is the average horizontal flow velocity?

A 0.20 m/s B 0.40 m/s C 0.25 m/s D 0.30 m/s

Question 8 ప్రశ్న 8

A horizontal-flow grit chamber must convey Q = 0.20 m^3/s at a specified mean velocity of 0.25 m/s. What flowing cross-sectional area is required?

A 0.50 m^2 B 1.25 m^2 C 0.80 m^2 D 0.05 m^2

Question 9 ప్రశ్న 9

A single rectangular grit channel carries 0.24 m^3/s at a design horizontal mean velocity of 0.30 m/s and a flowing water depth of 1.00 m. What flowing width is required?

A 0.60 m B 1.25 m C 1.80 m D 0.80 m

Question 10 ప్రశ్న 10

A grit channel has effective flow-path length 15 m and a uniform mean horizontal velocity of 0.25 m/s. What is the nominal travel or detention time along that path?

A 30 s B 75 s C 45 s D 60 s

Question 11 ప్రశ్న 11

For a horizontal-flow grit channel designed at a mean velocity of 0.25 m/s and a specified nominal travel time of 60 s, what effective channel length is required?

A 15 m B 24 m C 10 m D 3.75 m

Question 12 ప్రశ్న 12

At a design discharge of 0.12 m^3/s, a grit-removal unit is assigned a nominal hydraulic detention time of 50 s. What operating water volume is required?

A 2.4 m^3 B 12.0 m^3 C 6.0 m^3 D 0.0024 m^3

Question 13 ప్రశ్న 13

A target grit particle settles at 0.020 m/s in an ideal quiescent-water approximation. How long does it take to settle vertically through a 1.20 m water depth?

A 40 s B 60 s C 24 s D 120 s

Question 14 ప్రశ్న 14

An ideal horizontal grit channel is 1.00 m deep; the target grit has settling velocity 0.025 m/s and horizontal mean water velocity is 0.30 m/s. Neglecting inlet and outlet allowances, what minimum effective settling length is required for a particle entering at the free surface?

A 7.5 m B 15.0 m C 20.0 m D 12.0 m

Question 15 ప్రశ్న 15

For an ideal horizontal-flow grit chamber, the design discharge is 0.15 m^3/s and the target particle settling velocity is 0.025 m/s. Ignoring nonideal-flow allowances, what minimum plan surface area corresponds to Q/vs?

A 6.0 m^2 B 0.00375 m^2 C 3.0 m^2 D 37.5 m^2

Question 16 ప్రశ్న 16

A rectangular horizontal grit channel has effective length 13.5 m, flowing depth 0.90 m and mean horizontal velocity 0.30 m/s. What minimum grit settling velocity is needed for a particle entering at the water surface to settle by the outlet in an ideal trajectory model?

A 0.030 m/s B 0.015 m/s C 0.020 m/s D 0.045 m/s

Question 17 ప్రశ్న 17

A total sewage flow of 0.18 m^3/s is distributed equally to two identical rectangular grit channels, each 0.60 m wide with a water depth of 0.75 m. What is the mean flow-through velocity in each channel?

A 0.40 m/s B 0.20 m/s C 0.10 m/s D 0.30 m/s

Question 18 ప్రశ్న 18

A peak sewage flow of 0.48 m^3/s is to be divided among identical duty grit channels, each carrying water 0.80 m wide and 1.00 m deep at a limiting mean flow velocity of 0.30 m/s. What is the minimum number of such duty channels needed, excluding standby provision?

A 1 B 3 C 4 D 2

Question 19 ప్రశ్న 19

An ideal horizontal grit basin handles 0.16 m^3/s with plan surface area 8.0 m^2. Target grit has settling velocity 0.025 m/s. Which assessment follows from ideal overflow-rate theory?

A Surface loading is 0.020 m/s, below the target settling velocity; ideal full-depth removal is hydraulically feasible. B Surface loading is 0.050 m/s, so the target grit must be fully removed. C Surface loading is 0.020 m/s, but any grit with settling velocity above this must remain in suspension. D Surface loading is independent of flow and plan area, so no assessment is possible.

Question 20 ప్రశ్న 20

A plant has average sewage flow 12 MLD and an explicitly assumed peak factor of 2.4. At that peak flow, a velocity-controlled grit channel is sized for 0.30 m/s. What total flowing cross-sectional area is required?

A 0.33 m^2 B 0.83 m^2 C 1.11 m^2 D 2.40 m^2

Question 21 ప్రశ్న 21

Which statement correctly compares typical retention and motion in conventional horizontal-flow and aerated grit chambers?

A Aerated chambers must have zero detention time because air immediately removes grit. B Aerated grit chambers commonly use a few minutes of detention with helical mixing, whereas velocity-controlled horizontal channels commonly use roughly one minute as a reference. C Both types must use the same exact detention time regardless of peak flow and required particle capture. D Horizontal-flow chambers rely entirely on air-induced spiral motion and aerated chambers rely solely on a proportional weir.

Question 22 ప్రశ్న 22

After removing mineral grit from raw sewage, the collected material still contains significant putrescible organic matter. What is the most appropriate downstream grit-handling step?

A Return all recovered grit to biological aeration without separation. B Add more raw sewage to the grit hopper to make the mixture easier to transport. C Store wet, organic-rich grit indefinitely in an open pile at the plant. D Wash and classify the grit to reduce adhering organics before suitable dewatering and disposal.

Question 23 ప్రశ్న 23

A sewage treatment plant processes 24 ML/day and measured grit generation is 0.075 m^3 per ML of sewage. What daily volume of collected grit should be used for a simple storage estimate?

A 1.8 m^3/day B 0.075 m^3/day C 0.32 m^3/day D 18 m^3/day

Question 24 ప్రశ్న 24

The mean longitudinal velocity of an existing horizontal-flow grit chamber rises from 0.25 m/s to 0.45 m/s after a peak-flow increase, with chamber geometry unchanged. Which operational concern becomes more likely?

A Excessive gravitational settling of light organic solids caused by the increased velocity. B Automatic improvement in capture of all fine grit sizes at the outlet. C Carryover or resuspension of grit because higher horizontal velocities leave less settling time and can cause scour. D Guaranteed reduction in mechanical wear downstream because grit is carried more quickly.

Question 25 ప్రశ్న 25

A horizontal grit channel shows adequate grit settling at peak flow but excessive organic deposition at low flow. Which operational modification directly addresses the probable hydraulic cause?

A Increase the detention time further by reducing low-flow velocity. B Use a suitably designed proportional control weir or Parshall-type flow-control arrangement to help maintain the intended flow-through velocity across variable flows. C Remove upstream screens so more solids enter the chamber and accelerate grit settling. D Increase the channel depth without analysing how this changes velocity or sedimentation.

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