Inclined Plate Settlers

Inclined Plate Settlers enhance sedimentation by providing multiple shallow settling zones within existing clarifier basins, dramatically reducing required footprint for particle removal. Parallel plates installed at 45-60° angles create laminar flow conditions that allow particles to settle onto plate surfaces and slide down for collection, rather than requiring full basin depth settling. Municipal installations typically achieve 2-4x capacity increases in existing clarifiers, with surface loading rates reaching 1,200-2,000 gpd/ft² compared to 600-800 gpd/ft² for conventional settling. The primary limitation is susceptibility to fouling from biological growth and debris accumulation, requiring regular maintenance access and cleaning protocols that many older facilities struggle to accommodate.

• Primary Clarification Enhancement: Installed in existing circular clarifiers (30-100 ft diameter) to increase capacity 2-3x without basin expansion. Plates reduce surface overflow rates from 800-1000 gpd/sf to 400-500 gpd/sf. Connected upstream from RAS pumping, downstream to secondary treatment. Selected when plant capacity increases exceed clarifier hydraulic limits.
• Tertiary Filtration Pretreatment: Located between secondary clarifiers and multimedia filters in 5-25 MGD plants. Reduces TSS from 15-25 mg/L to 5-10 mg/L, extending filter runs from 24-36 hours to 48-72 hours. Downstream connects to filter influent channel. Selected to minimize filter backwash frequency and chemical usage.
• Phosphorus Removal Systems: Integrated with chemical precipitation (alum/ferric) in dedicated basins. Handles 2-15 MGD flows with detention times of 45-90 minutes. Upstream receives coagulated water, downstream connects to effluent weirs. Selected for reliable phosphorus removal to <1.0 mg/L without biological processes.

Daily Operations: Operators monitor effluent turbidity (target <5 NTU), check for uneven flow distribution across plates, and observe sludge blanket depth using clarity tubes. Flow adjustments maintain 0.5-1.5 gpm/sf loading rates. Visual inspection identifies plate fouling or damage requiring cleaning cycles.

​

Maintenance: Monthly high-pressure washing (1500-2000 psi) removes biofilm buildup on plates. Quarterly inspection of support structures and hardware torque. Annual plate module removal for detailed cleaning and replacement of damaged sections. Requires confined space entry permits and fall protection equipment. Maintenance staff need basic mechanical skills for module handling.

​

Troubleshooting: Uneven settling indicates hydraulic short-circuiting from damaged plates or improper flow distribution. Rising effluent turbidity signals excessive loading or sludge carryover. Plate modules typically last 15-20 years before replacement.

• Inclined Plate Modules: Corrugated PVC or polypropylene plates at 55-60° angles, 24-48 inches long. Spacing of 2-3 inches between plates creates settling channels. Standard modules are 4x8 or 6x8 feet for easy handling. Selection based on required surface area and maintenance access requirements.
• Support Structure: Hot-dip galvanized steel framework supporting plate modules above basin floor. Designed for 50-75 psf live loads including ice formation. Includes walkways and handrails meeting OSHA requirements. Sizing accommodates thermal expansion and seismic loads per local codes.
• Sludge Collection System: Chain-and-flight or traveling bridge mechanisms beneath plates. Operates continuously or intermittently (2-4 cycles/day). Scraper speeds of 2-6 ft/min prevent resuspension. Selection depends on basin geometry and sludge production rates of 200-800 lbs/day per MGD.
• Effluent Weirs: Adjustable weirs maintaining uniform flow distribution across plate width. V-notch or rectangular configurations with 6-12 inch adjustment range. Stainless steel construction for corrosion resistance. Sized for peak flows without drawdown exceeding 0.1 feet.

• Surface Loading Rate (SLR): 600-1,200 gpd/ft² for primary clarification; 400-800 gpd/ft² for secondary clarification. Higher rates acceptable with upstream coagulation/flocculation.
• Plate Angle: 55-60° from horizontal optimizes settling efficiency while preventing solids accumulation. Steeper angles (>60°) increase short-circuiting risk.
• Plate Spacing: 2-3 inches typical for municipal applications. Closer spacing improves efficiency but increases maintenance and head loss (0.5-2.0 feet typical).
• Length-to-Spacing Ratio (L/S): 12:1 minimum, 20:1 optimal for Reynolds numbers 200-500. Shorter ratios reduce removal efficiency significantly.
• Upflow Velocity: Maximum 15 ft/hr in plate zone to prevent resuspension. Design for 8-12 ft/hr under peak flow conditions.
• Detention Time: 15-30 minutes total basin residence time, with 60-80% occurring in settling zone upstream of plates.
• Plate Materials: Polypropylene or PVC modules rated for continuous 140°F operation. Fiberglass acceptable but requires UV stabilization for outdoor installations.
• Removal Efficiency: 80-90% TSS removal typical for primary applications; 85-95% for secondary with proper upstream treatment.

• What surface loading rate should I design for given my upstream processes? Plants with effective coagulation/flocculation can operate at 1,000+ gpd/ft²; those without should stay below 800 gpd/ft². Wrong decision results in poor effluent quality and potential permit violations. Need influent TSS data, particle size distribution, and upstream chemical addition capabilities.
• Should I retrofit existing clarifiers or build new settler tanks? Retrofit viable when existing tank depth >8 feet and adequate sludge removal exists. New construction better for plants lacking proper inlet/outlet hydraulics. Wrong choice wastes 30-50% of potential capacity improvement. Requires detailed hydraulic modeling and structural analysis.
• What plate configuration optimizes my specific application? Cross-flow designs handle higher solids loading (>200 mg/L TSS) but require more maintenance. Counter-current flow maximizes efficiency for lower solids applications. Incorrect selection reduces performance 20-40% and increases operating costs. Need accurate influent characterization and maintenance capabilities assessment.
• How do I size for peak flow while maintaining efficiency? Design plates for 1.5-2.0x average flow with variable speed drives on sludge removal equipment. Undersizing causes washout during peaks; oversizing wastes capital. Requires 5-year flow projection and diurnal variation analysis.

• Division 40 - Process Integration
• Section 40 05 23 - Water Treatment Clarification Equipment
• Secondary: Section 46 05 33 - Potable Water Clarifiers (drinking water plants)

• Material/Equipment Verification: Verify plate material (PVC, polypropylene, fiberglass) meets project specs; Confirm plate spacing and angle per design drawings; Check support structure materials and coatings
• Installation Requirements: Level foundation critical - 1/8" tolerance typical; Crane access needed for large plate modules; Temporary dewatering often required
• Field Challenges: Plate alignment during installation; Access for future maintenance; Integration with existing piping
• Coordination Issues: 12-16 week lead times for custom configurations; Early electrical coordination for sludge removal systems

• Parkson Corporation - AquaDaf clarifier systems, widely used in municipal applications with proven track records at facilities like Aurora, CO and Tigard, OR
• WesTech Engineering - Superpulsator and conventional settler designs serving plants from 1-50 MGD
• Evoqua Water Technologies - Accelator package units popular for smaller municipalities
• Aqua-Aerobic Systems - AquaDAF systems with integrated dissolved air flotation capabilities

• Conventional Settling - 30-40% lower capital cost, larger footprint, better for variable loads
• Dissolved Air Flotation (DAF) - Superior for low-density floc, 20-30% higher cost but faster startup
• Ballasted Flocculation (Actiflo) - Highest rate loading, 50-100% premium cost, excellent for peak flow management
• Membrane Bioreactors - Eliminates settling entirely, 3-4x cost but produces higher quality effluent

Establish strong manufacturer relationships early - field support during startup is invaluable for optimizing performance. Consider standardizing on one manufacturer's plate design across multiple basins to simplify spare parts inventory. Specify removable plates even if initially more expensive; the maintenance access pays dividends. Many successful installations include plate washing systems from day one rather than retrofitting later.