34 Questions
What is the primary purpose of the 'Minimal National Standards' (MINAS) for industries?
To ensure that industries take anti-pollution measures within their techno-economic capability
Under what circumstances can MINAS be relaxed?
Under no circumstances
Who is empowered to prescribe standards stricter than MINAS?
The State Pollution Control Boards
What is the concept developed by the Central Pollution Control Board (CPCB) to designate water bodies?
Designated best use
How many 'designated best uses' has the CPCB identified?
5
What is the primary purpose of the 'designated best use' concept?
To determine the quality of water required for a specific use
What is the importance of environmental education in the context of pollution?
It plays a crucial role in negating the adverse impacts of pollution
What is the main challenge in addressing environmental degradation?
Complexity of environmental problems
What is the recommended maximum particle size of suspended solids for inland surface water?
850 microns
What is the purpose of implementing environmental laws?
To take proactive steps to prevent environmental degradation
What is the maximum permitted suspended solids in marine/coastal areas for process wastewater?
100 mg/L
What is the significance of having a firm hand in implementing environmental protection laws?
To ensure effective implementation of laws
What is the hindered settling velocity represented by?
uH
What is the value of n in Stoke's law region?
4.6
What is the formula for bulk density?
ρb = ρs(1 - ε) + ρfε
What is the assumption in the ideal sedimentation basin about the distribution of flow?
Uniform horizontal velocity entering the settling zone
What happens to particles that enter the sludge zone?
They remain in the sludge zone
What is the characteristic of the upflow clarifier?
The velocity of the rising water is greater than the settling velocity of the particle
What happens to the area through which the water passes as it rises in the upflow clarifier?
It increases
What is the purpose of the settling zone in the sedimentation basin?
To remove particles from the water
What is the condition for particles to be completely removed from a horizontal flow sedimentation tank?
ut ≥ vo
What is the typical flow velocity range used when piping flocculated water to the settling tank?
0.15 to 0.6 m/s
What is the percentage of particles removed (P) with a settling velocity of vt in a horizontal flow sedimentation tank designed with an overflow rate of v0?
$\frac{vt}{vo} * 100$
What is the maximum horizontal velocity through the tank that does not allow resuspension of settled particles?
Scour velocity (VH)
What is the purpose of the diffuser wall in the settling tank?
To reduce the flow velocity and spread the flow evenly
What is the recommended head loss through the holes in the diffuser wall?
4 to 5 times the velocity head
What is the value of the cohesion constant (k) for sticky interlocking matter?
0.6
What is the typical diameter of the holes in the diffuser wall?
0.10 to 0.20 m
What is the expression for the scour velocity (VH) in a horizontal flow sedimentation tank?
$\frac{8k \rho_p - \rho_f}{gD_p}f$
What is the purpose of controlling horizontal flow velocities in the settling zone?
To reduce turbulence and scour particles
What is the condition for the ratio of length to width in a rectangular classifier?
At least 6
What is the condition for the overflow rate in a horizontal flow sedimentation tank?
At least four times the settling velocity
What can be used to check on turbulence and back-mixing in the settling zone?
Reynolds and Froude numbers
What is the condition for the horizontal velocity in a horizontal flow sedimentation tank?
At most one-third of the scour velocity
Study Notes
Environmental Protection and Pollution Control
- Environmental degradation is a complex issue that requires a multi-dimensional approach.
- Environmental education can play a crucial role in negating the adverse impacts of pollution.
General Standards for Discharge of Environmental Pollutants
- Part-A: Effluents
- Suspended solids: maximum 100 mg/L (inland surface water), 600 mg/L (public sewers), 200 mg/L (land for irrigation)
- Particle size: shall pass 850 micron IS Sieve
Minimal National Standards (MINAS) for Industries
- CPCB lays down specific standards for effluents discharged from industries
- Standards are based on techno-economic capability of the industry to take anti-pollution measures
- MINAS cannot be relaxed, but State Pollution Control Boards can prescribe stricter standards if necessary
Primary Water Quality Criteria
- CPCB has developed a concept of "designated best use" for water bodies
- 5 designated best uses have been identified
Hindered Settling
- Hindered settling velocity (uH) = us
- Methods to calculate uH: Stoke's law region (very small particles), Newton's law region (large particles)
Ideal Sedimentation Basin
- Assumptions: discrete particle settling, four zones in the basin (inlet, outlet, sludge, and settling), even distribution of flow and particles
- Particles that enter the sludge zone are captured and remain in the sludge zone
Sedimentation Zones
- Horizontal flow clarifier
- Upflow clarifier
- Settling in an upflow clarifier: particles having settling velocity ut ≥ vo will be completely removed
Scour Velocity
- Maximum horizontal velocity through the tank that does not allow resuspension (scouring) of settled particles
- Formula: VH = (8k ρp - ρf) gDp / (f ρf)
Design of a Municipal Wastewater Plant
- Flow rate: 60000 m3/d
- Target particle characteristics: DP = 200×10-6 m, k = 0.05, f = 0.025, ρP = 1.25×103 kg/m3
- Design considerations: rectangular classifier, overflow rate, horizontal velocity, scour velocity, diffuser wall
Inlet Zone
- Velocity must be reduced and flow spread evenly over the cross section of the settling tank
- Diffuser wall is used to accomplish this
- Port velocities: 0.20 to 0.30 m/s, hole diameter: 0.10 to 0.20 m, spacing: 0.25 to 0.60 m apart
Learn about environmental degradation, education, and pollution control measures, including standards for discharge of environmental pollutants.
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