Vertical Flocculators

Vertical flocculators promote particle aggregation through controlled vertical mixing in tall, narrow basins, typically achieving 10-30 minutes detention time. Water flows upward through multiple compartments with decreasing energy input from bottom to top, allowing coagulated particles to collide and form settleable flocs. These units typically achieve 85-95% turbidity removal when properly operated with optimal coagulant dosing. The primary trade-off is higher construction costs and deeper excavation requirements compared to horizontal alternatives, making them less suitable for sites with high groundwater or rock constraints.

• Water Treatment Plant Clarification: Vertical flocculators are integrated into conventional treatment trains between rapid mix and sedimentation basins in 2-25 MGD plants. They provide 15-30 minute detention times with gentle mixing (20-70 sec⁻¹ G-values) to grow settleable floc particles. Selected for compact footprint when site constraints limit horizontal basin construction.
• Package Plant Systems: Pre-engineered vertical flocculators serve 0.5-5 MGD facilities as combined flocculation/clarification units. These systems integrate mixing chambers with upflow clarifiers, reducing overall plant footprint by 40-60% compared to conventional horizontal designs. Ideal for smaller municipalities with limited capital budgets and operational staff.
• Retrofit Applications: Existing plants upgrade aging horizontal flocculators with vertical units to increase capacity within existing structures. Vertical designs can boost treatment capacity 25-40% while maintaining required detention times, making them cost-effective alternatives to complete plant expansions for 5-15 MGD facilities.

Daily Operations: Operators monitor impeller speeds via SCADA systems, adjusting G-values based on raw water turbidity and jar test results. Visual inspection of floc formation occurs through observation ports every 2-4 hours. Chemical feed rates require adjustment when floc characteristics change, with typical polymer doses ranging 0.5-2.0 mg/L.

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Maintenance: Monthly impeller inspections check for blade damage or buildup requiring 2-person confined space entry with gas monitoring. Quarterly gearbox oil changes and annual bearing replacements prevent costly failures. Drive belt tensioning occurs weekly, requiring basic mechanical skills and standard PPE including hard hats and safety harnesses.

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Troubleshooting: Poor floc formation indicates incorrect G-values or chemical dosing, while excessive energy consumption suggests impeller fouling or mechanical wear. Hydraulic short-circuiting appears as uneven floc distribution, requiring baffle adjustment. Equipment typically operates 15-20 years before major component replacement, with drive systems failing most frequently after 8-12 years of continuous operation.

• Mixing Impellers: Variable-speed drives control 4-8 foot diameter impellers generating 20-70 sec⁻¹ G-values. Fiberglass or stainless steel construction with 5-25 HP motors. Selection based on basin geometry and required energy dissipation rates.
• Tapered Basin Geometry: Circular or square basins with decreasing cross-sectional area create declining velocity gradients from 70 sec⁻¹ (inlet) to 20 sec⁻¹ (outlet). Concrete construction with 12-25 foot depths for 15-30 minute detention times.
• Baffle Systems: Vertical baffles create serpentine flow patterns preventing short-circuiting. Removable fiberglass or concrete baffles spaced 3-6 feet apart with 1-2 foot gaps at alternating ends.
• Inlet/Outlet Structures: Rapid mix discharge enters through submerged ports with energy dissipation. Outlet weirs or submerged orifices maintain proper hydraulic gradients. Stainless steel construction with adjustable elevation controls.

• Flow-Related Parameters:
• Design flow rate: 0.5-50 MGD (0.35-34.7 cfs)
• Peak flow capacity: 1.5-2.5x average daily flow
• Hydraulic loading rate: 0.5-2.0 gpm/ft² (typical 1.0-1.5 gpm/ft²)
• Detention time: 15-45 minutes (typical 20-30 minutes)
• Velocity gradient (G): 20-75 sec⁻¹ (typical 30-50 sec⁻¹)
• Physical Dimensions:
• Tank depth: 12-20 feet (typical 14-16 feet)
• Length-to-width ratio: 3:1 to 5:1
• Baffle spacing: 18-36 inches
• Baffle depth: 80-85% of water depth
• Around-the-end velocity: 0.5-1.5 fps
• Performance Criteria:
• Floc formation efficiency: >90% particle aggregation
• Head loss through baffles: 0.1-0.3 feet
• Power dissipation: 0.5-2.0 hp/MG
• Temperature range: 32-85°F operational
• Turndown ratio: 25-100% of design flow
• Water Quality:
• Turbidity reduction: 50-80% through flocculation
• pH range: 6.5-8.5
• Coagulant dose compatibility: 5-50 mg/L alum equivalent

• What is the required velocity gradient range for your raw water characteristics? High turbidity (>50 NTU) requires G-values of 50-75 sec⁻¹, while low turbidity (<10 NTU) needs 20-40 sec⁻¹. Wrong selection results in poor floc formation or floc breakup. Need: historical turbidity data, seasonal variations, coagulant type.
• Should you design for constant or variable velocity gradients through the basin? Tapered flocculation (decreasing from 60 to 20 sec⁻¹) improves performance but increases complexity and cost by 15-25%. Constant G-value simplifies operation but may reduce efficiency by 5-10%. Need: budget constraints, operator skill level, performance requirements.
• What detention time provides optimal floc development for your application? Cold water (<40°F) requires 30-45 minutes, warm water needs 15-25 minutes. Insufficient time produces weak flocs; excessive time wastes basin volume and may cause floc deterioration. Need: seasonal temperature data, downstream clarifier requirements.
• How will you handle flow variations while maintaining effective flocculation? Fixed baffles work for flows within ±25% of design; adjustable baffles or multiple trains needed for wider variations. Poor turndown capability reduces treatment efficiency during low-flow periods. Need: flow variation analysis, operational flexibility requirements.

• Primary: 40 05

• Material/Equipment Verification
• Verify 316SS shafts and bronze bearings for corrosion resistance
• Confirm motor IP ratings and explosion-proof classifications
• Installation Requirements
• Crane access for shaft installation (typically 12-20 ft lengths)
• Precise basin dimensions for proper paddle clearances
• Electrical coordination for VFD integration
• Field Challenges
• Shaft alignment critical - misalignment causes premature bearing failure
• Concrete tolerances affect paddle clearances
• Coordination Issues
• Lead times: 16-20 weeks for custom configurations
• Early motor specifications needed for electrical design

• WesTech Engineering - VersaFloc vertical paddle flocculators, widely used in 1-50 MGD plants
• Evoqua Water Technologies - Vertical shaft flocculators with variable speed drives
• Xylem/Leopold - Vertical turbine mixers for flocculation basins
• Tonka Equipment - Custom vertical paddle systems for smaller municipal applications (0.5-5 MGD)

• Horizontal Paddle Flocculators - Better for rectangular basins, 10-15% lower cost, easier maintenance access
• Hydraulic Flocculation - No moving parts, lowest O&M, requires more head loss (2-4 ft typical)
• Air Mixing Systems - Good for retrofit applications, moderate energy costs, less effective in cold weather

Establish relationships with local manufacturer reps early - they provide valuable sizing verification and can expedite delivery for emergency replacements. Consider standardizing on one manufacturer across multiple basins to reduce spare parts inventory. Specify removable paddle assemblies for easier maintenance. Many operators prefer mechanical drives over VFDs for reliability, despite energy savings potential.