Sludge Dewatering with Decanter Centrifuge (DDE): Working Principle, Selection & Operation

The decanter centrifuge operates on centrifugal force (G-force) to separate phases by density. The conical-cylindrical bowl rotates at high speed, generating a force field many times that of gravity. This forces the heavier solid phase outward against the bowl wall, while the lighter liquid phase remains on the inside.

Inside the bowl, a scroll (conveyor screw) rotates in the same direction but at a differential speed relative to the bowl. This speed differential enables the scroll to continuously scrape the solid sludge layer along the bowl wall toward the conical end and discharge it, while the clarified liquid (effluent) overflows at the cylindrical end on the other side. This allows solid-liquid separation to occur continuously, without stopping the machine to discharge solids.

In wastewater treatment, sludge typically has low solids content and fine particles, so flocculant polymer must be dosed before the sludge enters the decanter to aggregate fine particles into larger flocs, improving separation efficiency and producing a drier sludge cake.

Each sludge dewatering technology has its own strengths. The decanter centrifuge is typically selected when the plant needs to handle high sludge flow rates, continuous operation, and a closed system with minimal odor emission. The table below provides a qualitative comparison to help select the right technology for each requirement.

The decanter is suitable for municipal wastewater treatment plants, food and beverage factories, textile dyeing, paper, chemical, and many other industries with stable or highly variable sludge flow rates. When fine-phase separation (liquid-liquid) is required rather than solid-liquid separation, a disk-stack separator is used — this is a different equipment category within the HAUS product range.

Sludge cake dryness is not determined by a single parameter but results from the interplay of multiple factors. Understanding these variables helps optimize operation and avoid polymer waste.

With the bowl range of 200-800 mm and flow rates of 1-180 m³/h, the DDE series covers a wide range of treatment plant scales, from small stations to high-capacity plants. Selecting the correct machine size should be based on actual sludge characteristics and design flow rate.

Wetted-parts components on the DDE series are manufactured from AISI 304 or 316 stainless steel. AISI 304 meets the requirements of most standard wastewater applications, while AISI 316 offers better corrosion resistance in environments with chlorides or high corrosivity. Material selection should be based on the sludge composition of each specific plant.

Operation is controlled via PLC: the system monitors bowl speed, scroll differential speed, and torque for stable running, and automatically adjusts when the sludge load changes. With closed and automated operation, the decanter significantly reduces manual labor and limits odor emission compared to open sludge pressing methods.

To maintain consistent performance, periodic maintenance schedules are required for the scroll, bearings, and polymer dosing system. Scroll wear caused by abrasive sludge is a factor to monitor, especially with industrial sludge containing sand or hard particles.