Thickening Screw Press

Thickening screw presses dewater biosolids by mechanically compressing sludge through a perforated cylinder using an internal screw conveyor, separating water from solids without chemical conditioning. The rotating screw creates increasing pressure as material moves toward the discharge end, forcing water through screen openings while conveying thickened solids forward. Typical installations achieve 4-8% total solids concentration from 1-3% feed sludge, with polymer consumption ranging 8-15 lbs/dry ton. Primary limitations include moderate dewatering performance compared to belt filter presses and sensitivity to fluctuating feed characteristics, requiring consistent upstream processes for optimal performance.

• Primary Sludge Thickening: TSPs process primary clarifier underflow from 0.5-3% solids to 4-6% solids at 2-15 GPM per unit. Selected over gravity thickeners for space-constrained sites and consistent performance regardless of temperature. Thickened sludge feeds digesters or dewatering equipment.
• WAS Thickening: Handles waste activated sludge from secondary clarifiers, typically processing 0.3-1.2% solids to 3-4% solids. Polymer addition (2-8 lb/dry ton) essential for biological solids. Preferred over dissolved air flotation in plants under 10 MGD due to lower power requirements and simpler operation.
• Combined Sludge Processing: Many 5-25 MGD plants blend primary and WAS upstream of TSPs, achieving 4-5% outlet solids. Provides operational flexibility and reduces downstream digester volume requirements by 40-60% compared to unthickened sludge.

Daily Operations: Operators monitor inlet flow rates, polymer feed rates, and outlet solids consistency through visual inspection. Typical adjustments include polymer dosage (2-6 lb/dry ton) based on capture efficiency and screw speed (1-8 RPM) for optimal thickening. Flow distribution between multiple units requires attention during peak loading periods.

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Maintenance: Weekly bearing lubrication and screen cleaning prevent performance degradation. Monthly polymer system calibration and quarterly drive alignment checks standard. Confined space entry procedures required for internal inspections. Basic mechanical skills sufficient for routine maintenance, with manufacturer service recommended for major repairs.

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Troubleshooting: High filtrate turbidity indicates insufficient polymer or excessive loading. Unusual vibration suggests bearing wear or material buildup. Screen blinding from grease or debris reduces capacity 20-40%. Typical service life 15-20 years with proper maintenance, though screens may require replacement every 8-12 years in high-grit applications.

• Screw Conveyor: Helical flights on central shaft compress sludge along 8-12 foot length. Stainless steel 304/316 construction with variable pitch (decreasing from inlet to outlet). Shaft diameter ranges 9-24 inches for municipal applications, with 0.75-5 HP drive motors.
• Perforated Screen: Wedge-wire or perforated plate cylinder surrounds screw with 0.5-2mm openings. 316SS construction standard. Screen length determines retention time and thickening performance.
• Polymer Feed System: Dilution and metering equipment delivers 0.1-0.5% active polymer solution. Typically includes day tank, dilution water controls, and positive displacement pump sized for 2-10 GPM.
• Outlet Weir/Valve: Adjustable discharge mechanism controls back-pressure and residence time. Pneumatic or manual operation maintains consistent solids capture and cake dryness.

• Hydraulic Loading Rate: 2-8 gpm/ft² (typical 4-6 gpm/ft²) based on screen surface area. Higher rates risk solids carryover and reduced capture efficiency.
• Solids Loading Rate: 15-40 lbs/hr/ft² dry solids, with 20-25 lbs/hr/ft² optimal for primary sludge applications. Secondary sludge typically operates at lower end of range.
• Feed Solids Concentration: 0.5-4.0% TS input, with 1.5-2.5% typical for primary sludge. Lower concentrations require larger units and higher polymer dosing.
• Thickened Solids Concentration: 4-8% TS output for primary sludge, 3-6% TS for secondary sludge. Performance varies significantly with sludge characteristics and polymer optimization.
• Polymer Dosage: 2-8 lbs active polymer per dry ton of solids, with 4-6 lbs/ton typical. Dosage directly impacts operating costs and cake dryness.
• Screen Opening Size: 0.5-1.5mm wedge wire spacing, with 0.75mm standard for municipal applications. Smaller openings improve capture but increase maintenance.
• Differential Speed: 1-15 rpm between inner and outer screws, typically 3-8 rpm for optimal thickening without excessive wear.

• What feed solids concentration and variability will the unit handle? Units sized for <1.5% TS require 50-75% larger capacity than those handling 2.5-3% TS. Consequence: Undersizing leads to poor capture rates and hydraulic overloading. Need: 12-month solids data including diurnal and seasonal variations.
• Should the system include integral polymer preparation or rely on existing systems? Integral systems cost $15,000-30,000 more but provide optimized mixing and dosing control. Consequence: Poor polymer mixing reduces efficiency by 10-20% and increases chemical costs. Need: Existing polymer system capacity and reliability assessment.
• What level of automation and remote monitoring is required? Basic manual control versus PLC with SCADA integration differs by $25,000-50,000. Consequence: Manual operation increases labor costs and risks process upsets during operator absence. Need: Staffing levels, existing control system compatibility, and operational philosophy.
• How will the unit handle peak flow conditions? Sizing for average versus peak flows affects capital cost by 30-50%. Consequence: Undersizing causes solids washout during peaks; oversizing reduces efficiency at normal flows. Need: Detailed flow data and storage/equalization capacity upstream.

• Primary: Division 46 23 61 - Sludge Thickening Equipment
• Secondary: Division 40 44 00 - Water Treatment Equipment (if part of integrated treatment system)

• Material/Equipment Verification: Verify 316SS construction for all wetted parts, Confirm polymer feed system compatibility, Check motor sizing for peak torque conditions
• Installation Requirements: Requires 8-12 week lead times for custom sizing, Foundation must accommodate vibration isolation, Electrical classification per plant hazardous area requirements
• Field Challenges: Polymer feed line routing critical for performance, Access platforms often require field modification
• Coordination Issues: Interface with existing SCADA systems, Coordinate polymer storage expansion

• ANDRITZ - SEPCOM screw thickener series (0.5-15 MGD capacity)
• Huber Technology - ROTAMAT Ro9 thickening screw (municipal installations at 2-50 MGD)
• Parkson Corporation - AquaKlear screw thickener (proven in 1-25 MGD plants)
• SUEZ - Densadeg screw thickener systems (integrated clarifier-thickener combinations)

• Belt Filter Press - Better for higher solids capture (95%+ vs 85-90%), but requires more operator attention and higher maintenance. Typically 20-30% higher capital cost.
• Centrifuge - Handles variable feed conditions better, higher throughput in smaller footprint. Operating costs 30-50% higher due to energy consumption.
• Gravity Thickener - Lower operating costs for larger plants (>10 MGD), but requires significantly more space and longer detention times.

Work directly with manufacturer applications engineers during design - they often identify site-specific optimization opportunities that reduce polymer consumption 15-25%. Request factory acceptance testing for critical installations over 5 MGD. Negotiate service agreements including annual calibration and wear part replacement schedules. Consider standardizing on single manufacturer across multiple plants to leverage bulk purchasing and simplified spare parts inventory.