Screening in Wastewater Treatment
- What is screening in wastewater treatment ?
- Types of screens (Based upon openings)
- Design information related to Manual and Mechanical Bar screen
- Important formulas used in design of screen chamber
- How to calculate number of bars in screen chamber?
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What is screening in wastewater treatment ?
Screening is a generally done to remove coarse materials from the flow stream to avoid
- Damage to subsequent parts, processes and equipment’s of wastewater treatment plants.
- Reduction in the overall treatment efficiencies.
- Reduces the chance of contamination in further treatment processes.
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Types of screens (Based upon openings)
- Coarse screen (6-150 mm)
- Fine screen (<6 mm)
- Micro screen (<0.5 µm)
Types of screening methods
- Manual Cleaning
- Machine based/mechanical Cleaning
- Chain Driven type
- Reciprocating type
- Catenary type
- Continuous belt type
- Static wedge wire type
- Drum type
- Step type
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Design information related to Manual and Mechanical Bar screen are as follows
| Description | Manual | Mechanical |
|---|---|---|
| Width of Bar | 5-15 mm | 5-15 mm |
| Depth of Bar | 25-38 mm | 25-38 mm |
| Clear spacing b/w bars | 25-50 mm | 15-75 mm |
| Provide slope (Degree) | 30-45 ° | 30 ° |
| Approach Velocity | 0.3-0.6 m/s |
Max. – 0.6-1.0 m/s Min. – 0.3-0.5 m/s |
| Max Head loss | 150 mm | 150-600 mm |
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Important formulas used in design of screen chamber
Coarse Bar Screen
Head loss through coarse bar screen
H = Head loss in meters
C = Discharge coefficient (0.7 for clean screen, 0.6 for clogged screen)
V = Velocity of flow through bar openings (m/s)
v = Approach velocity in upstream channel (m/s)
g = Acceleration due to gravity (9.81 m/s²)
H = Head loss in meters
C = Discharge coefficient (0.7 for clean screen, 0.6 for clogged screen)
V = Velocity of flow through bar openings (m/s)
v = Approach velocity in upstream channel (m/s)
g = Acceleration due to gravity (9.81 m/s²)
Fine Bar Screen
Head loss through fine bar screen
H = Head loss in meters
C = Discharge coefficient (0.7 for clean screen, 0.6 for clogged screen)
Q = Wastewater flow rate (m³/d)
A = Effective open area of submerged screen (m²)
g = Acceleration due to gravity (9.81 m/s²)
H = Head loss in meters
C = Discharge coefficient (0.7 for clean screen, 0.6 for clogged screen)
Q = Wastewater flow rate (m³/d)
A = Effective open area of submerged screen (m²)
g = Acceleration due to gravity (9.81 m/s²)
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How to calculate number of bars in screen chamber
Number of Bars (N) =
Channel Width − Bar Spacing
Bar Width + Bar Spacing
Number of bars spacing = Number of bars + 1
Area of screen opening = (number of bar spaces) × (bar spacing) × (water depth)
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Screen Channel Diagram
Ready for the Test?
[screeningbasics_quiz]