Sedimentation Principle

Suspended particles heavier than water settle under gravity. Quiescent conditions in clarifier allow settling without turbulence. Clarified water overflows at periphery. Settled solids accumulate at bottom for removal.

Circular Clarifier Design

Cylindrical tank with center feed well distributing influent, radial flow pattern to periphery, launder collecting overflow, rotating rake mechanism moving settled sludge to center collection pit, sludge drawoff, clarified water outlet.

Rectangular Settling Tank

Rectangular basin with inlet at one end, length providing retention time, weir overflow at outlet end, chain or flight scrapers moving sludge to collection hopper, clarified effluent discharge.

Surface Loading

Design parameter gallons per day per square foot surface area. Typical 300-800 gpd/sf for municipal water, 500-1200 gpd/sf for industrial applications. Loading rate depends on particle settling velocity and required clarity.

Retention Time

Hydraulic detention time 2-4 hours for water treatment, 1-3 hours for industrial wastewater. Adequate time allows particles reaching bottom before overflow. Depth typically 10-15 feet balancing retention versus construction cost.

Material Construction

Concrete most common for large clarifiers. Steel tanks with coating for smaller units. FRP for corrosive applications. Mechanism components in corrosion-resistant materials.

Chemical Pretreatment

Coagulant like alum or ferric chloride destabilizes particles. Polymer flocculant forms larger flocs settling faster. Chemical addition with rapid mix then gentle flocculation before clarification.

Sludge Collection

Rotating rakes in circular clarifiers move settled solids to center pit. Scrapers in rectangular tanks push sludge to end hopper. Sludge concentration typically 1-4% solids. Pumps or gravity transfer to thickening or dewatering.

Overflow Rate

Clarified water flows over weir at periphery or end. Weir loading 10,000-20,000 gpd per linear foot. V-notch weirs provide uniform flow distribution. Baffles prevent short-circuiting.

Applications

Municipal water treatment raw water clarification, industrial process water treatment, wastewater primary settling, cooling tower blowdown clarification, mining process water, and any application requiring gravity solid-liquid separation.

Performance Monitoring

Turbidity measurement on influent and effluent. Sludge blanket level detectors prevent carryover. Flow measurement enables loading rate calculation. Adjustments optimize performance.

Automation

Sludge withdrawal frequency and duration automated based on blanket level. Overflow rate monitoring. Chemical feed paced to flow. Mechanism torque monitoring detects problems.

Performance Benefits

Simple proven gravity separation technology. Large capacity in single unit. Relatively low operating costs. Handles varying loads with proper design.

Construction Standards

Concrete design per ACI codes. Steel tanks per AWWA standards. Mechanism per manufacturer specifications. Complete documentation with hydraulic design and capacity calculations.

ERGIL clarifier and settling tanks provide reliable gravity separation removing suspended solids from water and wastewater in municipal and industrial applications.