Carrousel® Oxidation Ditch

Carrousel® systems have offered a reliable way to treat wastewater since the late 1970s. With over 700 installations, in the US alone, the solution has low energy usage and great reliability. Many innovations have been introduced over the last decades and Ovivo's systems easily meet the most stringent effluent criteria, including low Total Nitrogen and Phosphorus.
EliminatIR™ Gate
The EliminatIR™ gate allows for simple control of nitrate recycle in a Carrousel system that incorporates a pre-anoxic zone (the denitIR® Carrousel® process).
Excell® Aerator
The Excell®aerator is the most efficient surface aerator on the market today. It imparts velocity to the channels and delivers oxygen to the mixed liquor.
Ovivo® Surface Aerators
Ovivo provides a variety of surface aerators. The Excell® aerator provides the latest and most efficient evolution surface aeration technology. Our upper and lower impeller design performs two functions simultaneously. The upper impeller for aeration and propulsion and the lower impeller for propulsion and for maintaining solids in suspension when dewatering a basin.
The Oculus™ System
The Oculus™ system reduces effluent ammonia, nitrate, total nitrogen and total phosphorus nutrients in Carrousel® systems using minimal amounts of energy.
Anaerobic 1st Anoxic Aerobic 2nd Anoxic Re-Aeration Effluent (mg/L)



AlternatIR™ SYSTEM




*May require trim doses of metal salts

Ovivo sells the Carrousel® system under a license agreement. For further information about the availability of this product, please contact our Customer Contact Center. Carrousel® is a registered trademark of DHV BV.

Ovivo offers competitive turnkey and traditional upgrade and retrofit pathways for your existing systems, even if you don’t already have a Carrousel system.

Upgrading your existing Carrousel System has never been easier or more worthwhile. Improve your efficiency, reduce your maintenance, or automate your process. Ovivo provides estimates for services and return on investment with a custom-made appraisal of your existing infrastructure.

You won’t be disappointed you called.

Ovivo sells the Carrousel® system under a license agreement. For further information about the availability of this product, please contact our Customer Contact Center. Carrousel® is a registered trademark of DHV BV.

How do Carrousel systems protect against storm flows?

Carrousel systems have a large amount of internal mixing. Each drop of water passes through the aeration zone 100 times before it leaves over the effluent weir. This allows for a dampening effect of the organic loading. The new EliminatIR™ gate can also be used to store solids during peak events.

How can Carrousel systems treat to such low nutrient limits?

Carrousel systems have been around since the advent of nutrient removal in the United States, the late 1970s. A combination of dedicated volumes (aerobic, anoxic, and anaerobic) with unlimited and free (no pumps required) internal recycle allows for a TN of less than 3 mg/L and a TP of less than 0.3 mg/L, or even lower. Recent research has suggested that the combination of repeated floc shear in the aeration zones and the reflocculation in the long channel zones significantly enhances simultaneous nitrification/denitrification as well.

Why do Carrousel systems meet low nutrient limits so consistently?

The power turndown of the Excell aerator can reach 90%, so DO (dissolved oxygen) control even at low flows is no problem. Preventing overation is the key to good, consistent biological nutrient removal, and lack of power turndown is a reason so many other systems fail or need large amounts of chemicals to make up for this deficiency. In addition, the free internal recycle (with no pumps) from the aeration zone to the anoxic zone can reach very high values (IR/Q can be >10), allowing for large denitrification rates.

Are Carrousel systems large in volume?

Carrousel systems are designed like any system that operates with CSTR (complete stirred tank reactor) kinetics using common activated sludge modeling software (although Ovivo does use a proprietary model for biological treatment and optimum hydraulics). The long SRT (solids retention time) systems are a thing of the past. Most Carrousel systems are designed at a 6 to 15 day SRT depending on climate and treatment objectives.

Are Carrousel systems large in footprint?

Carrousel systems can be much deeper in SWD (sidewater depth) than competing systems. With draft tube aerator technology and our unique Excell aerator, designs of 23-25 feet SWD are possible. We have three such systems operating in the United States.

Why are Carrousel systems so popular?

Quite simply, Carrousel systems are the most operator-friendly system on the market that can easily meet the most stringent permit limits in the United States.

Is there a license fee required?


What configuration is needed for my plant?

In general, refer to the flow sheets available. Ovivo process engineers will develop a proposal specific to your plant.

How many Carrousel system installations are out there?

Over 700 Carrousel systems have been installed in the United States alone!



The Ovivo Carrousel Process Team, which consists of decades of biological wastewater treatment plant design and innovation, has provided expertise and design assistance for wastewater treatment plants consisting of all shapes, sizes, and effluent permits.


  • Detail Design Support
  • Process Calculations
  • Equipment SizingProcess Guarantees
  • Extended Warranties
  • Retrofit Expertise
  • Process Training
  • Equipment Startup
  • Ovivo Connect (Asset Management)

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