Types of Circular Thickeners June 1, 2025 sazenviro Post in Uncategorized In any sludge treatment line—whether for municipal STPs or industrial ETPs—thickening plays a vital role in reducing sludge volume and preparing it for dewatering or digestion. The most widely used method for this is the circular gravity thickener, which uses sedimentation to concentrate solids in the sludge stream. This article explains the working principle of gravity thickeners, explores various types of circular thickeners, and provides practical guidelines for choosing the right sludge thickener manufacturer for your application. What Is a Gravity Thickener?Contents1 What Is a Gravity Thickener?2 Basic Working Principle of a Gravity Thickener2.1 Core Process Steps in a Gravity Thickener3 Key Components of a Circular Gravity Thickener3.1 Standard Equipment Supplied by a Sludge Thickener Manufacturer4 Design Parameters for Gravity Thickeners5 Types of Circular Gravity Thickeners5.1 Conventional Gravity Thickener5.2 High-Rate Gravity Thickener5.3 Lamella-Based Gravity Thickener6 Advantages of Gravity Thickeners6.1 Why Choose a “Gravity Thickener” Over Mechanical Options?7 Automation and Monitoring in Modern Thickeners8 Application Scenarios9 Top Global Sludge Thickener Manufacturers9.1 Selecting the Right Sludge Thickener Manufacturer10 Case Study: Circular Gravity Thickener for a Food Processing ETP (Kenya)11 Installation and Maintenance Tips11.1 Best Practices from a Sludge Thickener Manufacturer12 Common Design Mistakes to Avoid13 Conclusion A gravity thickener is a circular or rectangular tank that allows solids in sludge to settle under gravity. As solids settle, water is displaced and flows over a weir. The result is thickened sludge at the bottom, with clarified supernatant at the top. Gravity thickeners are energy-efficient and typically used before centrifuges, filter presses, or sludge digesters. Basic Working Principle of a Gravity Thickener Core Process Steps in a Gravity Thickener Influent DistributionSludge enters through a central feedwell that distributes it evenly and dissipates inlet velocity to maintain laminar flow. Settling ZoneSuspended solids settle downward by gravity as radial flow proceeds outward. Sludge ConsolidationSettled solids are slowly moved to the sludge hopper by rotating scraper arms. Supernatant CollectionClarified water overflows from a peripheral weir into a launder for return or disposal. Sludge RemovalThickened sludge (3–6% solids) is extracted from the hopper bottom via pumps or gravity drains. Key Components of a Circular Gravity Thickener Standard Equipment Supplied by a Sludge Thickener Manufacturer Component Description Feedwell Central inlet pipe with diffuser plate to reduce turbulence Rotating Bridge Carries the rake arm and scum skimmer mechanism Sludge Rake Arm Scrapes settled sludge to the central hopper Drive Unit Turns the rake arm; includes torque sensors Sludge Hopper Conical structure for sludge collection and discharge Overflow Weir Circular trough to collect clarified liquid Access Platform Bridge or deck for maintenance and motor access Design Parameters for Gravity Thickeners Proper gravity thickener performance depends on several sizing and operational factors: Parameter Typical Range Diameter 5 – 40 meters Side Water Depth (SWD) 2.5 – 4.5 meters Solids Loading Rate (SLR) 50 – 120 kg/m²/day Hydraulic Overflow Rate 0.1 – 0.3 m³/m²/hr Output Solids Concentration 3 – 6% dry solids Sludge Retention Time 4 – 12 hours (depends on sludge type) Designs must be tailored to influent sludge characteristics, including flow rate, TSS, temperature, and organic load. Types of Circular Gravity Thickeners Conventional Gravity Thickener Most common design Large diameter (10–30 m) with low overflow rate Mechanically rotated scraper with peripheral effluent weir Preferred for municipal STPs and general industrial sludge High-Rate Gravity Thickener Designed for higher solids loading Uses optimized feedwell hydraulics and shorter retention times Smaller footprint than conventional thickeners Often integrated with polymer dosing for rapid flocculation Suitable for paper, mining, and high-solids industrial sludge Lamella-Based Gravity Thickener Combines gravity thickening with inclined plate settlers Enhances settling by increasing effective surface area Ideal for compact ETPs with high TSS in a small footprint Offers rapid solids concentration with high efficiency Advantages of Gravity Thickeners Why Choose a “Gravity Thickener” Over Mechanical Options? Energy EfficiencyNo high-speed motors—just a low-power rake mechanism Simple OperationContinuous thickening without complex control systems Lower MaintenanceMinimal moving parts, no pressurized or high-speed systems Cost-EffectiveLow CAPEX and OPEX for plants with sufficient footprint Enhanced Dewatering PerformancePre-thickened sludge improves filter press or centrifuge efficiency Automation and Monitoring in Modern Thickeners Reputed sludge thickener manufacturers now offer integrated automation for improved efficiency: Sludge Blanket Level Sensor – Ultrasonic sensors monitor sludge depth Torque Monitoring System – Detects rake overload to prevent motor burnout SCADA/PLC Integration – Enables remote control, alerts, and data logging Polymer Dosing System – Enhances sludge flocculation and solids capture Application Scenarios Industry Typical Sludge Type Recommended Thickener Type Municipal STPs Waste Activated Sludge (WAS) Conventional gravity thickener Pulp and Paper Fibrous sludge High-rate or lamella thickener Textile Mixed biological and dye Lamella-based gravity thickener Metal Finishing Chemical hydroxide sludge Conventional thickener with cone hopper Mining Tailings, abrasive slurry High-rate gravity thickener with abrasion-resistant rake Top Global Sludge Thickener Manufacturers Selecting the Right Sludge Thickener Manufacturer Manufacturer Specialty WesTech (USA) High-rate and conventional thickeners for mining and water utilities EnviroChemie (Germany) Modular gravity thickening systems with compact layout Ovivo (Canada) Advanced rake drives and overflow collection SAZ ENVIRO (India) International supplier of circular gravity thickeners (up to 40m diameter) with automation-ready features for industrial ETPs and STPs across 20+ countries SAZ ENVIRO offers custom-designed units in FRP, MSRL, SS 304/316, or RCC, suitable for both export and domestic markets. Case Study: Circular Gravity Thickener for a Food Processing ETP (Kenya) Flow: 30 m³/day sludge stream Design: 6 m diameter × 3 m SWD circular tank Output: Thickened sludge from 1.2% → 5.5% DS Result: 40% reduction in centrifuge cycles 25% savings in polymer usage ROI in <14 months Installation and Maintenance Tips Best Practices from a Sludge Thickener Manufacturer Always include baffles around the feedwell to reduce turbulence Periodically inspect and calibrate torque limiters Drain sludge frequently to avoid “rafting” or rising sludge Clean overflow weirs regularly to avoid supernatant quality issues Maintain motor and gearbox as per OEM guidelines Common Design Mistakes to Avoid Mistake Consequence Oversized rake speed Resuspension of sludge, turbidity Inadequate hopper slope Sludge accumulation and clogging Missing torque sensor Potential for motor burnout No scum removal provision Floating solids over effluent weir Conclusion A well-designed gravity thickener is a cornerstone of effective sludge management. Whether your plant handles municipal or industrial effluent, selecting the right thickener type and manufacturer ensures reliability, regulatory compliance, and cost-efficiency. By understanding the working principle and different types—conventional, high-rate, and lamella—you can tailor the thickener system to your specific sludge profile and treatment goals. A trusted sludge thickener manufacturer can guide you through sizing, material selection, automation options, and long-term support to make your investment truly sustainable.