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 ______. Correct answer is '9'. Can you explain this answer?

Question

Answer

Given :
Grit chamber
Diameter of particle to be removed, d = 0.25 mm
Specific gravity, G = 2.7
Velocity of particles, V_s = 2.5 cm/ss
Width of chamber, B = 0.5 m
Waste water of flow, Q = 9720 m³ /d
Depth of flow, Y = 0.75 m

Minimum length of chamber required to remove 0.25 diameter particle is 9 m.

Answer

. Suppose two rectangular grit chambers are being used in parallel to treat waste water population of 90,000 with water consumption of 2501/c/d. And it is designed to all particles with an average diameter of 0.03mm with specific gravity of 2.40. of each settling zones is 4m wide by 15m long and 1.5m deep. Take dynamic of water = 0.001002Ns/m² The size viscosity Evaluate if the surface overflow rate will allow the intended grit settling. If not recommend a solution.

from a

remove

a)

b) Evaluate the adequacy of horizontal velocity, if organic material has the same diameter and a specific gravity of 1.20. Recommend a solution if required.

Answer

To determine the minimum length of the grit chamber, we need to consider the settling velocity of the particles, the flow-through velocity, and the dimensions of the chamber.

1. Terminal Settling Velocity:
The terminal settling velocity of the particles is given as 2.5 cm/s. Since we need to remove particles with a diameter of 0.25 mm, we can calculate the settling velocity using Stokes' Law:

Vt = (g * (diameter)^2 * (specific gravity - 1)) / (18 * viscosity)

Here, g is the acceleration due to gravity (9.81 m/s^2), diameter is 0.25 mm (0.00025 m), specific gravity is 2.70, and the viscosity of water is 1.0 x 10^-3 Ns/m^2.

Plugging in these values, we can calculate the terminal settling velocity as approximately 0.0356 m/s.

2. Flow-through Velocity:
The flow-through velocity needs to be maintained at 0.3 m/s. This velocity ensures that the particles are carried along without settling.

3. Chamber Dimensions:
The chamber has a width of 0.50 m and a depth of flow of 0.75 m.

4. Calculation:
To ensure complete removal of particles, the settling velocity of the particles should be less than the flow-through velocity. Therefore, we can set up the following equation:

0.0356 m/s < 0.3='' />

Solving for the minimum length of the chamber, we can rearrange the equation:

Length > (Flow rate * settling velocity) / (Width * depth of flow)

Given that the peak wastewater flow is 9720 m3/d, we can convert it to m3/s:

Flow rate = 9720 m3/d / (24 hours/day * 3600 s/hour) ≈ 0.1125 m3/s

Plugging in the values, we can calculate:

Length > (0.1125 m3/s * 0.0356 m/s) / (0.50 m * 0.75 m)

Length > 9.52 m

Since the length cannot be smaller than 9.52 m to ensure complete removal of particles, the minimum length of the chamber is 9 m (rounded down to the nearest integer).

Therefore, the correct answer is '9'.

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