Settling Tanks
Gravity clarification systems for primary and secondary treatment providing reliable solids-liquid separation
Overview
What is Settling Tanks?
Settling tanks, also known as clarifiers or sedimentation basins, utilize gravity to separate suspended solids from wastewater. These fundamental treatment units serve critical roles in both primary treatment (removing raw solids before biological treatment) and secondary treatment (separating biomass from treated effluent). Proper clarifier design ensures effective settling while maintaining continuous flow through the treatment plant.
Primary clarifiers remove 50-70% of suspended solids and 25-40% of BOD through gravity settling, protecting downstream biological processes and reducing organic loading. Secondary clarifiers following biological treatment separate activated sludge or biofilm solids from treated water, producing clear effluent for discharge or tertiary treatment while returning settled biomass to maintain biological reactor populations.
Spans Envirotech provides comprehensive settling tank solutions including circular center-feed clarifiers, rectangular longitudinal flow tanks, and high-rate lamella settlers. Our designs incorporate optimized hydraulics, efficient sludge collection mechanisms, and scum removal systems to ensure consistent performance across varying loads and environmental conditions.
Process
Clarification Process
Inlet & Flow Distribution
Wastewater enters through center wells (circular) or inlet zones (rectangular) designed to distribute flow evenly and dissipate inlet energy, creating quiescent settling conditions.
Settling Zone
Particles heavier than water settle toward the tank floor at velocities determined by particle size, density, and upflow rate. Proper sizing ensures adequate detention time (1.5-2.5 hours).
Sludge Collection
Settled solids accumulate on the tank floor. Rotating scrapers (circular) or chain-driven flights (rectangular) continuously move sludge to collection hoppers for removal.
Clarified Water Overflow
Clarified water flows over peripheral weirs (circular) or end weirs (rectangular) designed for uniform overflow rates. Adjustable weirs maintain optimal hydraulic loading.
Scum Removal
Floating materials are swept by surface skimmers to scum troughs for removal. Effective scum removal prevents carryover and maintains effluent quality.
Benefits
Key Advantages
- Simple gravity-based operation requires minimal energy input
- Handles high flow rates with large surface areas
- Removes 50-70% of influent suspended solids in primary treatment
- Secondary clarifiers enable activated sludge biomass separation and return
- Robust design with long service life and minimal maintenance
- Scalable from small package plants to large municipal facilities
- Can be retrofitted with lamella plates to increase capacity 2-3x
Applications
Industries & Use Cases
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