Floating Skimmer

Floating skimmers remove oils, greases, and other low-density materials from water surfaces in municipal treatment processes by continuously collecting floating contaminants through adjustable weirs or suction systems. These units automatically adjust to water level fluctuations while maintaining consistent skimming depth, typically removing 85-95% of visible surface oils in primary clarifiers and dissolved air flotation systems. The primary limitation is their dependence on sufficient surface area and relatively calm conditions - they become less effective in high-turbulence environments or when treating emulsified oils that don't readily separate and float.

• Primary Clarifiers (0.5-50 MGD): Floating skimmers remove grease, oils, and floating debris that rise during primary settling. Positioned at effluent end, they discharge collected material to scum pits or digesters. Selected for continuous operation and ability to handle variable scum thickness without manual intervention.
• Secondary Clarifiers: Remove biological foam and floating sludge in activated sludge systems. Critical in plants with filamentous bulking issues where sludge floats rather than settles. Connects to waste activated sludge lines or separate foam handling systems.
• Dissolved Air Flotation (DAF) Units: Essential component in DAF systems for removing floated solids. Operates continuously across water surface, collecting concentrated sludge blanket. Feeds directly to sludge thickening or dewatering processes.
• Equalization Basins: Removes oils and floating debris in industrial waste receiving facilities, preventing downstream process interference.

Daily Operations: Operators visually inspect skimmer rotation, blade contact with water surface, and scum discharge flow. Monitor drive motor amperage and adjust blade height for optimal collection. Check collection trough for proper drainage and clear any debris blocking discharge lines. Typical inspection time 5-10 minutes per unit.

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Maintenance: Monthly lubrication of drive gearbox and bearing assemblies. Quarterly blade inspection and adjustment. Annual drive motor service and torque limiter calibration. Requires basic mechanical skills and standard PPE (hard hat, safety glasses, non-slip footwear). Confined space entry procedures needed for some repairs.

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Troubleshooting: Common failures include blade wear causing poor surface contact, drive motor overload from debris accumulation, and bearing failure from inadequate lubrication. Warning signs include irregular rotation, increased motor amperage, and poor scum removal efficiency. Typical service life 15-20 years with proper maintenance.

• Rotating Skimmer Arm (6-150 ft diameter): Aluminum or stainless steel construction spans clarifier diameter. Rotates 0.1-2 RPM via central drive unit. Sizing based on clarifier diameter and expected scum loading rates.
• Collection Trough/Beach: Stainless steel trough collects skimmed material. Adjustable height mechanism accommodates varying water levels. Typical capacity 2-20 GPM depending on plant size.
• Drive Mechanism: Gear-reduced electric motor (0.25-2 HP) provides continuous rotation. Includes torque overload protection and variable speed capability for optimization.
• Skimmer Blade: Adjustable polyethylene or rubber blade maintains contact with water surface. Replaceable design with 2-5 year service life.
• Support Structure: Center pier or bridge-mounted system supports rotating assembly. Includes access platforms and safety features per OSHA requirements.

• Skimming Rate: 0.5-15 GPM per skimmer unit for municipal clarifiers
• Clarifier Diameter: 20-200 ft diameter (typical municipal range)
• Scum Blanket Thickness: Design for 0.25-2.0 inches typical depth
• Water Level Variation: ±6 inches standard, ±12 inches maximum operating range
• Skimmer Speed: 0.5-3.0 ft/min peripheral velocity (adjustable VFD control)
• Collection Efficiency: >90% surface removal at design loading rates
• Surface Loading Rate: 300-800 GPD/SF clarifier surface area
• Scum Production: 0.1-0.5 GPD/1000 gallons treated (varies by season/plant)
• Hydraulic Loading: Size pumps for 2-3x average scum production
• Temperature Range: 32-120°F operating (freeze protection required)
• Wind Loading: Design for 90 mph sustained winds (outdoor installations)
• Seismic: Follow local building codes for mechanical equipment

• Skimmer Configuration Selection - Should we specify tube-type, chain-and-flight, or rotating arm skimmers? Tube skimmers work best for <100 ft diameter clarifiers with minimal debris. Chain-and-flight systems handle larger clarifiers (>120 ft) and heavy scum loads. Rotating arms suit 60-150 ft clarifiers with moderate scum production. Wrong selection leads to poor collection efficiency and high maintenance.
• Drive System Sizing - What motor horsepower and gear ratio meets site conditions? Standard 0.5-2.0 HP motors with 50:1 to 200:1 reduction ratios. Undersizing causes stalling in heavy scum; oversizing wastes energy. Need scum production data, clarifier geometry, and seasonal loading variations.
• Scum Pump Integration - Should skimmer discharge to dedicated scum pumps or gravity collection? Pumped systems (5-25 GPM capacity) suit remote clarifiers; gravity works for adjacent scum wells. Consider elevation differences, pipe runs, and scum consistency. Wrong choice creates operational bottlenecks.
• Level Control Strategy - Fixed-depth or floating weir design? Floating weirs maintain 1-3 inch skimming depth automatically; fixed systems require level control. Floating designs cost 15-25% more but reduce operator intervention and improve efficiency in variable flow conditions.

• Primary: Division 46 23 61 - Clarification Equipment (Skimming Systems)
• Secondary: Division 40 20 00 - Process Water Treatment Equipment
• Note: Some specifications include under Division 46 21 00 (Sedimentation Equipment) when integrated with clarifier packages

• Material/Equipment Verification: Verify 316SS construction for all wetted parts, Confirm motor ratings match site electrical specifications, Check cable length against actual basin dimensions
• Installation Requirements: Crane access for initial placement and maintenance, Electrical connections require waterproof junction boxes, Anchor point installation often requires diving contractor
• Field Challenges: Basin dewatering typically required for anchor installation, Cable management systems prone to tangling during startup, Scum trough alignment critical for proper discharge
• Coordination Issues: Coordinate with clarifier manufacturer for mounting hardware, HVAC considerations for motor control panels in cold climates
• Lead Times: Standard units typically 12-16 weeks; custom configurations 20-24 weeks

• Lakeside Equipment - Raptor Complete Plant floating skimmers, widely used in 1-50 MGD plants with proven municipal track record
• WesTech Engineering - Floating Scum Skimmers with variable speed drives, common in western US facilities
• Evoqua (formerly Envirex) - E-series floating skimmers, established in many older municipal installations
• Schlumberger Water Services - CONTRA-SHEAR skimmers, popular in Canadian municipal markets

• Fixed Bridge Skimmers - Lower maintenance, preferred for smaller plants (<5 MGD), roughly 30% less expensive but limited flexibility
• Rotating Scum Scrapers - Integrated with sludge collection, common in package plants, similar cost but less effective for variable scum loads
• Manual Skimming - Still used in small facilities (<1 MGD), minimal capital cost but high labor requirements and inconsistent performance

Establish service relationships early - floating skimmers require more frequent maintenance than fixed equipment, and manufacturer support is critical for cable/drive issues. Many plants save 15-20% by purchasing spare drive components during initial procurement rather than emergency replacement. Consider redundant units for critical applications; single skimmer failures can compromise entire clarifier performance. Operator training on cable tensioning prevents 80% of mechanical failures.