Inline Baffled Grit Separator

Inline baffled grit separators remove sand, gravel, and other heavy inorganic particles from wastewater through velocity control and gravity settling within a channelized flow path. Strategically placed baffles create controlled turbulence and settling zones that allow particles larger than 0.2mm to settle while maintaining organic material in suspension. Typical removal efficiency ranges from 85-95% for particles above 0.2mm diameter at design flows of 2-4 fps through velocity. The primary trade-off is that effective grit removal requires consistent flow velocity control, making these units sensitive to significant flow variations and requiring careful hydraulic design to maintain performance across varying influent conditions.

• Primary Treatment Headworks (0.5-15 MGD): Installed downstream of bar screens and upstream of primary clarifiers. Selected for plants with limited space where separate grit chambers aren't feasible. Handles 2-8 fps velocities in 12"-48" pipelines, removing 65-75% of +100 mesh grit while maintaining hydraulic grade line.
• Pump Station Upgrades (1-25 MGD): Retrofitted into existing force mains before wet wells to protect downstream pumps. Chosen when centrifugal pumps experience excessive wear from sand infiltration. Typical installations use 18"-36" units handling 1,500-8,000 GPM.
• Secondary Treatment Protection (5-50 MGD): Positioned before biological treatment systems where primary clarifiers underperform. Protects fine bubble diffusers and RAS pumps from abrasive particles. Common in activated sludge plants with high I&I or combined sewer systems.
• Bypass/Emergency Lines: Installed in plant bypass configurations during wet weather events, providing basic grit removal when primary treatment is bypassed.

Daily Operations: Operators monitor differential pressure across unit (typically 2-6" WC) and observe grit discharge consistency. Flow velocity verification through portable meters ensures 2-3 fps settling zone maintenance. Visual inspection of outlet clarity indicates separation efficiency, with manual grit discharge 1-3 times per shift depending on influent loading.

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Maintenance: Weekly hopper cleanout prevents compaction, requiring confined space entry procedures and H2S monitoring. Monthly baffle adjustment and wear plate inspection. Quarterly bearing lubrication on adjustable components. Maintenance requires basic mechanical skills, standard PPE, and gas detection equipment for enclosed areas.

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Troubleshooting: Excessive head loss indicates baffle clogging or grit buildup, typically occurring after 2-4 weeks without cleaning. Reduced grit capture suggests velocity issues or worn baffles. Units typically require major component replacement after 8-12 years. Warning signs include unusual vibration, inconsistent grit discharge, and downstream pump wear increases.

• Inlet Baffle Assembly: Creates controlled turbulence and velocity reduction from 6-8 fps to 2-3 fps. Constructed from 304SS or fiberglass, sized at 1.5-2x pipe diameter. Selection based on expected grit loading and abrasion resistance requirements.
• Separation Chamber: Cylindrical or rectangular vessel providing 15-45 second detention time. Carbon steel with polymer lining or concrete construction for 24"-60" diameter units. Sized for 0.8-1.2 fps settling velocity.
• Grit Collection Hopper: Conical bottom section with 60° slopes for gravity discharge. Holds 2-8 cubic feet depending on plant size. Includes 4"-8" cleanout connections and level indicators.
• Outlet Baffle/Weir: Controls hydraulic profile and prevents grit re-entrainment. Adjustable height mechanism allows flow optimization. Stainless steel construction with 6"-24" adjustment range for varying flow conditions.

• Flow Velocity Control: Maintain 0.7-1.2 fps through grit chamber to ensure proper settling while preventing organic washout. Peak flow capacity typically 2.5-3x average daily flow.
• Detention Time: 45-90 seconds at peak hourly flow for effective grit removal. Shorter times reduce organics capture but may miss fine grit (>65 mesh).
• Surface Loading Rate: 500-1,200 gpm/ft² for horizontal flow-through design. Higher rates acceptable with proper baffle configuration but require validation testing.
• Grit Removal Efficiency: Target 95% removal of particles >65 mesh (0.21mm) at design flow. Specify removal rates for 100, 65, and 35 mesh sizes.
• Channel Dimensions: Width 4-20 feet, length 20-80 feet depending on flow. Length-to-width ratio typically 4:1 to 6:1 for optimal hydraulics.
• Baffle Spacing: Vertical baffles spaced 3-8 feet apart, extending 60-80% of water depth. Under-baffle clearance 12-24 inches.
• Grit Storage: Size for 3-7 day storage at 1-4 ft³/MG treated, depending on influent characteristics and cleaning frequency.
• Head Loss: Typically 2-6 inches through properly designed baffle system at peak flow.

• What peak flow capacity is required versus available footprint? Flows >15 MGD may require multiple parallel channels or alternative technology. Inadequate capacity causes grit carryover to downstream processes, increasing wear on pumps and blowers. Need 20-year flow projections and site constraints.
• Should design prioritize grit removal efficiency or organic rejection? Detention times >75 seconds improve fine grit capture but increase organic settling, creating septicity and odor issues. Plants with aggressive preliminary treatment may accept lower grit efficiency. Requires influent characterization and downstream process sensitivity analysis.
• What level of automation is justified for grit handling? Manual cleaning acceptable for <2 MGD plants with adequate staffing. Mechanical removal systems cost $150-400K but essential for larger plants or limited operations staff. Consider labor availability, safety requirements, and lifecycle costs.
• How will seasonal flow variations affect performance? Winter flows often 2-3x summer flows in northern climates. Adjustable weirs or variable baffle configurations maintain proper velocities. Requires local flow data and operational flexibility assessment.

• Division 40 - Process Integration
• Section 40 05 00 - Common Work Results for Process Integration
• Section 40 20 00 - Process Piping
• Primary: 40 05 00 covers inline process equipment integration. Secondary: 40 20 00 for associated piping and hydraulic connections within treatment train.

• Material/Equipment Verification:
• Verify 316SS construction for all wetted components
• Confirm screw conveyor torque ratings match design grit loads
• Review polymer feed system compatibility
• Installation Requirements:
• Level concrete pad ±1/4" over equipment footprint
• Overhead clearance for screw conveyor maintenance
• 480V/3-phase power with VFD provisions
• Field Challenges:
• Coordinating inlet/outlet piping elevations with existing structures
• Ensuring proper slope on grit discharge piping
• Coordination Issues:
• Lead times typically 16-20 weeks for standard units

• Lakeside Equipment - RAPTOR Complete Plant systems (0.5-50 MGD municipal references)
• Headworks International - HydroDynamic grit removal systems (extensive California installations)
• Smith & Loveless - GritKing packaged units (popular in Midwest municipalities)
• Evoqua Water Technologies - Grit-King inline systems (large municipal market presence)

• Vortex Grit Chambers - Better organics separation, higher capital cost (~40% premium)
• Aerated Grit Chambers - Superior for high organic loading, requires 60% more footprint
• Hydrocyclones - Compact retrofit option, limited to <5 MGD applications, similar capital costs but higher operating complexity

Establish manufacturer service agreements during procurement - grit systems require specialized knowledge for optimization. Budget 15-20% contingency for site-specific piping modifications; standard units rarely fit existing infrastructure perfectly. Consider oversizing screw conveyors by one size increment; grit loads often exceed design assumptions, and replacement costs far exceed initial upgrade investment.