Centrifuge Thickening and Dewatering: Efficient Solutions for Modern Biosolids Management Introduction

In wastewater treatment, centrifuge thickening and dewatering play a crucial role in reducing sludge volume, optimizing treatment efficiency, and minimizing costs for transport, storage, and disposal. These high-speed mechanical processes separate solids from liquids using centrifugal force—producing a dense “cake” that significantly lowers water content.

Centrifuges have been used since the 1930s, evolving into one of the most efficient and compact dewatering systems available. By removing water early in the process, wastewater plants can reduce digester and storage tank size, lower fuel use, and streamline downstream processing.

How Centrifugal Thickening Works

A centrifuge operates as a continuous-feed unit. Wastewater solids enter a rapidly rotating cylindrical bowl, where centrifugal force separates heavier solids from lighter liquids. Solids are moved by a scroll conveyor to discharge, while clarified liquid flows over the weir.

High-solids centrifuges feature conical bowls that promote drying along an inclined surface before discharge. Modern designs also use wear-resistant materials, high-torque drives, and automated controls for efficient and safe operation.

Advantages of Centrifugal Dewatering

Compared with traditional systems like belt filter presses or drying beds, centrifuge dewatering offers numerous advantages:

• High efficiency: Produces drier sludge (20–40% solids).
• Reduced costs: Cuts hauling, storage, and disposal expenses.
• Compact footprint: Requires minimal floor space.
• Automation-ready: Can run continuously with minimal operator supervision.
• Clean and safe: Low odor potential, minimal aerosol exposure.
• Durable: Major components can be easily replaced; suited for heavy-duty operation.

However, operators must consider power consumption, noise, and specialized maintenance due to high rotational speeds.

Applications in Wastewater Treatment

Centrifuge systems are adaptable across various scales and treatment stages:

• Thickening before digestion – Reduces the size of anaerobic digesters.
• Dewatering before disposal – Achieves solids levels that meet landfill or reuse criteria.
• Volume reduction for transport – Cuts biosolids volume by up to 50%.

For smaller facilities (<4 MGD), non-mechanical alternatives such as drying beds may still be cost-effective, but many modern plants find centrifuges worthwhile due to space, labor, and odor control benefits.

Design and Operational Considerations

To size and design an effective centrifuge system, engineers must evaluate:

• Daily volume of primary and waste-activated sludge
• Seasonal variation in solids generation
• Target solids concentration in the feed and cake
• Polymer system efficiency (mixing, aging, and blending)
• Automation potential and labor availability

Polymers play a key role in optimizing dewatering. Proper mixing, aging, and gentle blending enhance floc formation, improve centrate clarity, and increase cake dryness. Some facilities also use oxidizing agents like potassium permanganate to reduce odor and improve dewatering performance.

Performance Overview

Depending on sludge type and digestion method, Centrifuge Thickening and Dewatering systems can achieve the following solids concentrations:

Sludge Type	Feed Solids (%TS)	Cake Solids (%TS)
Primary (Undigested)	4–8	25–40
Waste Activated (Undigested)	1–4	16–25
Primary + WAS (Anaerobic)	2–4	22–32
Lime Stabilized	4–6	20–28

These results make centrifuges especially valuable in plants where space, odor control, and labor efficiency are critical design factors.

Operational Tips

For optimal performance of Centrifuge Thickening and Dewatering:

• Monitor feed rate, polymer dosage, and differential scroll speed.
• Conduct jar tests to check polymer conditioning.
• Keep accurate records of feed volume, cake solids, and centrate quality.
• Ensure grit removal to minimize wear.
• Allow for gradual start-up and shutdown to protect mechanical integrity.

Automation can extend operating hours without increasing staff time, making centrifuge systems ideal for both large and medium-sized facilities.

Cost Considerations

While centrifuges have higher upfront costs than belt presses, long-term operation and maintenance can be more economical.
Typical costs include:

• Polymer: $12–80 per dry ton of solids (DTS)
• O&M: $65–$209 per DTS
• Equipment installation: ~$650,000 for a medium-sized plant

When factoring in odor control, labor reduction, and footprint savings, centrifuges often deliver the lowest total lifecycle cost among dewatering options.

Conclusion

Centrifuge thickening and dewatering represent one of the most efficient, reliable, and compact solutions in modern wastewater management. With advancements in automation, materials, and polymer technology, these systems enable wastewater facilities to meet environmental compliance, reduce costs, and support sustainable biosolids reuse.

For additional technical resources and design guidelines, refer to the U.S. EPA Biosolids Technology Fact Sheets.