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Influent Screening
Considerations and Case
Histories
Brian Hannon P.E, Moore & Bruggink
Outline
• What is preliminary treatment? • Why is preliminary treatment important? ▫ Obvious Reasons
• Types of Screening Equipment ▫ General Screen Categories ▫ Screen Media ▫ Types of Fine Screens ▫ Process Considerations ▫ O&M Considerations
• Screening Case History ▫ Second and Third Order Effects
Preliminary Treatment – What?
• Critical component of wastewater treatment
• Removal of Inorganic and Unwanted Solids
▫ Hygiene Products (including WIPES!)
▫ Pavement debris/rocks
▫ Rags
▫ Sticks
▫ Plastics
▫ Grit
▫ Some grease/fat
▫ Hair (if needed)
▫ Volkswagens?
Images: CDC.gov
www.southernwater.co.uk
Preliminary Treatment – Types
• Screening
• Comminution
• Grit Removal
• Grease Removal
• Septic Acceptance
Images: CDC.gov www.southernwater.co.uk
Preliminary Treatment – Why?
• Prevents operational problems of downstream processes
▫ Blocked Flow
Pumps
Piping/Valves
Channels
Preliminary Treatment – Why?
• Prevents operational problems of downstream processes
▫ Sensitive Processes
Membrane Bioreactors
IFAS
MBBR
Trickling Filters
Preliminary Treatment – Why?
• Prevents operational problems of downstream processes
▫ Sensitive Processes
Membrane Bioreactors
IFAS
MBBR
Trickling Filters
Preliminary Treatment – Why?
• Prevents operational problems of downstream processes
▫ Decreased capacity in unit processes
Anaerobic Digesters
Aerobic Digesters
Sludge Storage Tanks
Wetwells
Preliminary Treatment – Why?
• Decreases maintenance of downstream equipment
▫ Impeller wear
▫ Pump Ragging
▫ Pump Seals
▫ Pump Bearings
▫ Clogged Pipelines
Preliminary Treatment – Why?
• Decreases maintenance of downstream equipment
▫ Impeller wear
▫ Pump Ragging
▫ Pump Seals
▫ Pump Bearings
▫ Clogged Pipelines
Preliminary Treatment – Why?
• Decreases maintenance of downstream equipment
▫ Impeller wear
▫ Pump Ragging
▫ Pump Seals
▫ Pump Bearings
▫ Clogged Pipelines
Prevention of Ragging
• Valves Stuck in Place
• Diffusers not Working
• Undue Stress on Equipment
• Money spent to clean
Screening Equipment - General
• Categories
▫ Trash Racks/Bypass Screens = >36mm openings
▫ Coarse Screens = 6mm to 36mm openings
▫ Fine Screens = 0.5mm to 6mm openings
▫ Microscreens = < 0.5mm openings
Screening Equipment - General
• Categories
▫ Trash Racks/Bypass Screens = >36mm openings
▫ Coarse Screens = 6mm to 36mm openings
▫ Fine Screens = 0.5mm to 6mm openings
▫ Microscreens = < 0.5mm openings
Screening Equipment - General
• Categories
▫ Trash Racks/Bypass Screens = >36mm openings
▫ Coarse Screens = 6mm to 36mm openings
▫ Fine Screens = 0.5mm to 6mm openings
▫ Microscreens = < 0.5mm openings
Consider BOD and TSS removal percentages and possible energy savings!
Screening Equipment – Screen Media
• Types of Media
▫ Perforated Plate
▫ Bars
▫ Wedge Wire
▫ “Teardrop”
▫ Mesh
▫ Other
Screening Equipment – Screen Media
• Types of Media
▫ Perforated Plate
▫ Bars
▫ Wedge Wire
▫ “Teardrop”
▫ Mesh
▫ Other
Screening Equipment – Screen Media
• Types of Media
▫ Perforated Plate
▫ Bars
▫ Wedge Wire
▫ “Teardrop”
▫ Mesh
▫ Other
Screening Equipment – Screen Media
• Types of Media
▫ Perforated Plate
▫ Bars
▫ Wedge Wire
▫ “Teardrop”
▫ Mesh
▫ Other
Screening Equipment – Screen Media
• Types of Media
▫ Perforated Plate
▫ Bars
▫ Wedge Wire
▫ “Teardrop”
▫ Mesh
▫ Other
Screening Equipment – Screen Media
• Types of Media
▫ Perforated Plate
▫ Bars
▫ Wedge Wire
▫ “Teardrop”
▫ Mesh
▫ Other
Fine Screening Equipment
• Types of Fine Screens
▫ Multi-rake driven screens
▫ Continuous Element
▫ Stair Screens
▫ Band Screens
▫ Drum Screens
▫ Inclined Cylindrical Screens
Fine Screening Equipment
• Types of Fine Screens
▫ Multi-rake driven screens
▫ Continuous Element
▫ Stair Screens
▫ Band Screens
▫ Drum Screens
▫ Inclined Cylindrical Screens
Fine Screening Equipment
• Types of Fine Screens
▫ Multi-rake driven screens
▫ Continuous Element
▫ Stair Screens
▫ Band Screens
▫ Drum Screens
▫ Inclined Cylindrical Screens
Fine Screening Equipment
• Types of Fine Screens
▫ Multi-rake driven screens
▫ Continuous Element
▫ Stair Screens
▫ Band Screens
▫ Drum Screens
▫ Inclined Cylindrical Screens
Fine Screening Equipment
• Types of Fine Screens
▫ Multi-rake driven screens
▫ Continuous Element
▫ Stair Screens
▫ Band Screens
▫ Drum Screens
▫ Inclined Cylindrical Screens
Fine Screening Equipment
• Types of Fine Screens
▫ Multi-rake driven screens
▫ Continuous Element
▫ Stair Screens
▫ Band Screens
▫ Drum Screens
▫ Inclined Cylindrical Screens
Fine Screening Equipment
• Types of Fine Screens
▫ Multi-rake driven screens
▫ Continuous Element
▫ Stair Screens
▫ Band Screens
▫ Drum Screens
▫ Inclined Cylindrical Screens
Screening Equipment
• Process Considerations
▫ Screen Size
▫ Screen Location
▫ Vertical Distance/Incline
▫ Headloss/Hydraulics
▫ Quantity of Screenings
▫ Washing/Compacting
▫ NPW
▫ Downstream Processes
▫ Bypassing Provisions
Screening Equipment
• Maintenance Considerations
▫ Materials of construction
Stainless
UHMWPE
▫ XP
▫ Underwater components
▫ Teeth/Bar Connection
▫ “Stapling”
▫ Bypassing Provisions
▫ Brush/Spray Bars
Case History
• Second and Third Order Effects
WHERE DO ALL THOSE RAGS GO?
Case History
• Previous screen
Case History
• Previous comminution and grit removal
Case History
• First Order Effect
▫ Influent Pumps Rag up
Case History
• Second Order Effect
▫ Ragging in aerobic digester tanks
Case History
• Third Order Effects ▫ Ragging in Sludge Thickener ▫ Ragging in Sludge Storage Tank
Case History
• Second Order Effect ▫ Rags from Primary Tanks into Anaerobic
Digester ▫ Positive Displacement Pumps ▫ Pumps rag up
• Third Order Effect ▫ Rags Build Up ▫ Outlet piping plugged ▫ Overflow piping plugged ▫ Pressure Relief Valve plugged
Case History
• Popped Cover, Overflow solids
Case History
• Popped Cover
Case History
• Rag mat buildup in digester after removing cover
Case History
• New Screens
Case History
• Lesson Learned
▫ Side Shields!
Case History
• New Raw Sewage Pumps
Case History
• New Grit Chamber
Benefits
• Decreased operations and maintenance costs
▫ Pump Ragging
▫ Plugged lines
▫ Less cleaning
▫ Less inorganics (more room for effective treatment)
▫ Better Safety for operators
