Grit Washer (Washer Compactor)

Grit washers, also called washer compactors, remove organic matter and debris from captured grit through mechanical washing and classification processes. The equipment typically uses an inclined screw conveyor with wash water sprays to separate inorganic grit (sand, gravel) from organic materials, achieving 95% or higher organic removal efficiency. Clean, washed grit can then be beneficially reused or disposed of at lower cost, while separated organics return to the treatment process. The primary trade-off is increased system complexity and maintenance requirements compared to simple grit disposal, though operational savings from reduced disposal volumes typically justify the investment.

• Headworks Grit Removal Systems (2-50 MGD): Grit washers are integrated downstream of vortex grit chambers or aerated grit basins to clean captured grit. The washer receives grit slurry at 10-20% solids, washing away organics and fines while compacting clean grit to 65-75% solids. This reduces disposal costs by 60-70% compared to unwashed grit.

• Combined Sewer Overflow (CSO) Facilities: During wet weather events, grit washers handle high-volume, contaminated grit from CSO screening operations. They're selected for ability to process variable loads (2-20 tons/day) and produce clean grit meeting landfill acceptance criteria.

• Lagoon Cleanout Projects: Mobile or temporary grit washing systems process accumulated solids during lagoon dredging operations. Washers separate reusable sand from organic waste, allowing beneficial reuse as construction material while minimizing disposal volumes by 40-50%.

Daily Operations: Operators monitor wash water clarity, grit moisture content (target 25-35%), and throughput rates via control panel indicators. Adjustments include wash water flow rates, screw speed (10-30 RPM), and discharge gate timing. Visual inspection of washed grit quality ensures organics removal meets disposal specifications.

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Maintenance: Weekly bearing lubrication and monthly drive chain/coupling inspection. Quarterly wear plate and screw flight replacement on high-volume units. Safety requires lockout/tagout procedures, confined space protocols for tank entry, and standard PPE plus cut-resistant gloves. Maintenance requires basic mechanical skills and overhead crane operation certification.

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Troubleshooting: High torque alarms indicate screw binding from oversized debris or bearing failure. Poor wash efficiency suggests worn spray nozzles or inadequate water pressure. Excessive fines carryover indicates improper overflow weir adjustment. Typical service life: 8-12 years for mechanical components, 15-20 years for vessels with proper maintenance.

• Washing Chamber: Stainless steel 316 vessel with internal spray manifolds delivering 40-60 PSI wash water. Sizing ranges from 4-12 cubic feet for municipal applications. Selection based on peak grit loading (typically 0.5-5 cubic feet per ton/day).

• Screw Conveyor/Compactor: Carbon steel or stainless steel helical screw (6-24 inch diameter) with variable pitch for washing and dewatering zones. Includes integrated drive system (2-10 HP) with torque monitoring for overload protection.

• Wash Water System: Recirculation pumps (5-25 HP), clarifier tank, and filtration to maintain wash water quality. Typical flow rates of 50-200 GPM with automated backwash cycles.

• Discharge Controls: Pneumatic or hydraulic gates controlling grit discharge consistency. Includes level sensors and automated cycling based on throughput requirements.

• Primary Sizing Parameters:

• Grit feed rate: 0.5-15 cubic feet per hour (typical municipal range)
• Wash water flow: 10-50 GPM at 40-60 PSI operating pressure
• Organic removal efficiency: 95-99% by weight (target specification)
• Grit particle size range: 0.2-2.0 mm diameter retention
• Throughput capacity: 50-500 pounds grit per hour (dry weight basis)

• Performance Requirements:

• Final grit moisture content: 8-15% by weight after washing/compacting
• Wash water turbidity reduction: >90% from inlet to overflow
• Power consumption: 2-10 HP depending on capacity and compaction requirements
• Availability factor: >95% with proper maintenance scheduling

• Physical Constraints:

• Footprint: 4x6 to 8x12 feet for standard municipal units
• Height clearance: 12-16 feet including discharge chute and maintenance access
• Foundation loading: 150-300 PSF depending on unit size and concrete pad requirements

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Critical for sizing: actual measured grit production rates from existing grit removal systems, not theoretical calculations, as field rates typically run 30-50% below design estimates.

• What is the actual grit production rate and characteristics? Requires 30-day sampling of existing grit removal systems. Undersizing by >20% leads to frequent overflow bypassing and reduced wash efficiency. Need specific gravity, particle size distribution, and organic content data from representative samples during peak loading periods.

• Should the system include integral grit dewatering or separate handling? Threshold: >2 cubic yards grit per day typically justifies integral dewatering/compacting. Wrong decision results in either over-investment in unnecessary features or inadequate moisture reduction requiring additional downstream processing and higher disposal costs.

• What wash water source and quality requirements apply? Plant effluent (turbidity <10 NTU) versus potable water affects sizing and performance. Poor quality wash water reduces organic removal efficiency below 90%, defeating the primary purpose. Need analysis of available water sources and any pretreatment requirements.

• How will washed grit be conveyed and disposed? Conveyor discharge versus truck loading affects equipment configuration and building requirements. Distance >50 feet to disposal point typically requires belt conveyor systems, impacting total project costs by 15-25%.

• MasterFormat Section 46 13 16 - Grit Removal Equipment (primary)

• Secondary reference: 46 13 13 - Screening Equipment (for integrated screening features)

• Material/Equipment Verification:

• Verify 316SS construction for all wetted parts
• Confirm polymer feed system compatibility with plant chemicals
• Check motor ratings for continuous duty cycle

• Installation Requirements:

• Concrete pad designed for dynamic loading
• Overhead crane access for maintenance
• Electrical classification per NEC 501 requirements

• Field Challenges:

• Achieving proper slope on grit discharge conveyor
• Polymer feed line freeze protection in cold climates

• Coordination Issues:

• Interface with upstream grit removal equipment
• Washwater return piping to headworks

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Lead times: 16-20 weeks typical.

• Headworks International - HeadCell HCU series (municipal standard, 0.5-50 MGD capacity)

• Smith & Loveless - PISTA Grit Washer models 6-72 (proven track record in smaller municipalities)

• Lakeside Equipment - RAPTOR Complete Plant systems with integrated washers

• Huber Technology - RoSF4 Grit Washer (European design, growing US presence in larger facilities)

• Grit Classifiers - Lower cost ($75K vs $150K), suitable when organic content <20%, no washing capability

• Hydrocyclones - Compact footprint, good for retrofits, higher maintenance requirements, similar cost range

• Dewatering Screw Conveyors - Basic dewatering only, 40% lower cost, acceptable when organics removal not critical

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Grit washers preferred when strict organics removal required or disposal costs high (>$50/ton).

Establish clear performance guarantees for organic removal (typically 95% reduction) and moisture content (<15%) in submittals. Many operators report better results when polymer feed systems are oversized by 25% beyond manufacturer recommendations. Build relationships with local manufacturer reps early - they often provide free startup assistance and troubleshooting support. Consider packaged systems to reduce field coordination issues and achieve better warranty coverage.