Excell® Aerator

The Excell® aerator with the high efficiency surface impeller and the floor-scouring lower turbine efficiently provides aeration at full speed and at 80-90% turndown (drawing 10-20% nameplate power), while still maintaining sufficient mixing in the basin. The Excell®aerator offers the best energy savings, mixing efficiency and dissolved oxygen control on the market.

The Excell®aerator is the most efficient surface aerator on the market today. It has been approved by Royal Hasking DHV, the singular independent worldwide authority on vertical shaft oxidation ditches, for use in Carrousel® Systems. Standard oxygen transfer efficiency is 3.85 lb O2/HP-hr. Power turndown can be as high as 90%, meaning the aerator speed may be slowed down to 10% nameplate power without mixing limitations.

The Excell® aerator is placed at the head of channel as it turns in a Carrousel® system and imparts velocity to the channels and delivers oxygen to the mixed liquor.

The Excell aerator with the high efficiency surface impeller and the floor-scouring lower turbine efficiently provides aeration at full speed and at 80-90% turndown (drawing 10-20% nameplate power), while still maintaining sufficient mixing in the basin. The Excell aerator offers the best energy savings, mixing efficiency and dissolved oxygen control on the market. For a first-hand account of the advantages Ovivo’s dual impeller Excell aerator, watch the attached video – http://youtu.be/oUzaFDXCVFs

The surface impeller is a rim blade design using a stabilizing star plate to reduce forces transmitted to the gear reducer. The lower impeller is a four bladed radial pumping design that maintains floor scouring velocity. The two impellers are connected on a common shaft with no bearings located below the water. The impeller assembly is coupled to a high service factor gear reducer and premium efficiency motor, both of which are fixed on a clean concrete deck.  Maintenance consists of greasing bearings every few weeks and yearly oil changes, all performed above the tank on the clean concrete deck.

Service life for the Excell aerator is over 20 years. Ovivo has many sites with similar equipment operating for 30 years.

Low speed surface Excell® aerators accomplish two functions –

As the name implies it aerates, or adds necessary oxygen to the mixed liquor.  The mixed liquor is a broad spectrum biological culture that metabolizes (oxidizes) pollutants in the wastewater.  The rotating inverted cone impeller achieves aeration of the mixed liquor.  The impeller literally throws the mixed liquor into the air where atmospheric oxygen diffuses into the water.  Microorganisms in the mixed liquor form pollutant oxidation, then utilizes this newly dissolved oxygen.

The second function of the Excell® aerator is to agitate the mixed liquor in order to keep the microorganisms in suspension and to provide a nominal 1-foot per second channel velocity throughout the basin.  Suspension of the active biomass is required so that adequate contact is made between the microorganisms and the wastewater, thus ensuring proper treatment and pollutant removal.

How is power and oxygen input controlled?

There are two methods of controlling power and therefore oxygen input—impeller submergence and impeller speed. The water level can be lowered relative to the impeller by an effluent weir to reduce the “bite” on the impeller blades. The difference between the high water level (submergence) and low water level (submergence) is generally less than one foot (30 cm). In general, lowering impeller submergence reduces power input and proportionally oxygen input by 40-50%.

Due to the inconvenience of raising and lowering effluent weir position (submergence) variable frequency drives are commonly used today to adjust the impeller rotation speed. Reducing the rotational speed by half (e.g., 40 rpm to 20 rpm) reduces power input and proportionally oxygen input by 70-80%.

Thus the combination of impeller submergence and speed adjustment can reduce power and oxygen input by 90%. Due to the lower turbine, the Excell® aerator can maintain mixing at these extreme power turndown conditions.

What is the oxygen transfer efficiency of the Excell® aerator?
Oxygen transfer efficiency of the surface impeller is 3.85 lb O2/HP-hr.
Your competitors says you don’t need the lower turbine. Is this true?
The lower turbine is recommended anytime you want the flexibility to adjust power to the incoming demand while still maintaining mixing and high oxygen transfer efficiency. This is generally desired to prevent over-oxygenation in nutrient removal plants and to save on energy bills. Operators also like the ability to maintain mixing during basin draining operations (after the water level falls below the surface impeller) to save on basin cleanout. Well over 100 facilities enjoy the benefits of the lower turbine.  Our competitors don’t offer the lower turbine, presumably to save cost on their equipment at the expense of operational flexibility.
Is the Excell® aerator available for retrofits?
Yes. Any Carrousel system or oxidation ditch provided by a competitor may be retrofitted. See the following video to see a successful retrofit.

How many installations are there?
Ovivo has over 2,000 low speed surface aerators installed in the United States, over 400 dual impeller aerators installed, and over 100 aerators with the Excell aerator design installed since it was developed in 2006.

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Carrousel® is a trademark of Royal Hasking DHV, B.V., The Netherlands.