New developments make Surface Aerators to an economic solution and offer in addition advantages that hardly any other system can realize. Surface aerators are manufactured in two variants, vertical shaft and horizontal shaft, the so called brush aerators.
Surface aerators are very often applied in the Carousel® systems. Thie principle of this design is the recirculation of the sludge in a continuous manner, so that it periodically passes through an aerobic and an anoxic area in alternating mode. The necessary propulsion of the sewage is created by the surface aerator as well, which makes this kind of device, particularly popular for such application.
Surface aeration advantages
While oxygen transfer efficiency is considered generally lower than that of fine bubble aeration systems, the new generation of vertical shaft surface aerators demonstrates a high aeration efficiency quite close to that of bubble aerations systems.
Vertical shaft aerators O2Max series
High efficiency aerator
Spaans Babcock developed the third generation aerator: After a long period of testing, the ideal design was developed. A complete new design which ensures a high efficiency, a huge mixing effect and a very smooth running with less vibration to the bridge and drive unit. The new O2Max is designed on the basis of the latest know-how (knowledge) on surface aeration and beats the old problems with this kind of aerators.
The O2Max is approved for the Carrousel® system by DHV.
The O2Max consists of:
The aerator impeller is a low speed, non-clogging and open type. The aerator is a heavy steel construction to withstand stresses created by mixed liquor motion and will be adequately anchored and supported to the bridge of the aeration tanks.The impeller consist of a flat plate with curved blades beneath the plate in order to obtain maximum efficiency and to suffer minimum friction losses between blades and water.
The O2Max is especially suitable for Carousel® systems. Due to its high oxygen input and propulsion properties, it is often the most economical solution for this system. Extra propellers are often not necessary, however, this will be examined on a case-by-case basis.
In cases where no bridge or platform construction are possible due to large water level changements, the installation with floaters is a possibility. Three floaters on a heavy load construction will allow the aerator to float itself.The aerator will be kept in its position by heavy steel cables. Installation is possible in all kind of square and round tanks.
The circulator is a construction of a floating aerator, connected in the middle of the tank and is moving self propelled on a circular path system through the tank. The system can be used for low load systems in all kinds of tanks. Installation is possible in relative large tanks.
The O2Max design will comply to the following:
O2Max aerator selection
O2max aerators cover the following range:
Motor power: 4 to 160kW
Standard O2 transfer rate: 11 to 300kgO2/h
Rotor diameter: 1100 to 3400mm
Tank volume: 80 to 8,000m3
Tank depth: 2 to 8m
Tank dimension: 7 to 32m (square tank, one aerator)
The selection is based on the Standard oxygen transfer rate under standard conditions (SOTR) of the O2Max® aerator, that depends on the aerator, the speed, the submergence of the aerator and the geometry of the aeration tank.
The load on a sewage treatment plant is varying almost continuously. Therefore the oxygen transfer capacity required is not constant as well. To optimize energy consumption the oxygen input of the aerator should be adjusted accordingly. There are two possibilities to adjust the power input and oxygen transfer of the aerator: by changing submergence or by changing speed.
The submergence range of a surface aerator is limited to a certain maximum and minimum value. Exceeding these values will cause reduction of efficiency. The variation of submergence can be created by changing the height of the aeration unit or by changing the water level. The last possibility is the cheapest but also the most time consuming.
At present the most popular way of regulating the power input of a surface aerator is by changing the speed. The speed of a surface aerator is limited to a certain maximum and minimum value. Exceeding these values will cause reduction of efficiency. The maximum and minimum speed for the O2Max® aerator is related to the diameter of the aerator and the peripherical speed. The peripherical speed is limited to about 6.5 m/s.
There are two methods of changing speed: application of a two speed motor or application of frequency control. With aid of a two speed motor the power input can be changed in steps from 100% at high speed to about 50% at low speed to zero when switched off. Applying a frequency control enables every power input in between 0% and 100%.
Although the low speed vertical shaft aerators are more often used for oxidation ditches / carrousel systems, the brush aerator is still alive. After 40 years, a design review was undertaken in 1998 by Spaans Babcock resulting in the O2Rotor.
In the past, brush aerators were introduced for use in oxidation ditches to bring oxygen and propulsion in to the water. While slowly rotating through the water and by splashing around, oxygen transfer will take place.
The O2Rotor is a robust, low speed aerator, with a high level of corrosion resistance due to the stainless steel blades and the coating system. By using quality steel for all the parts of the aerator instead of plastic the failures of broken and bent flights and tubes will be eliminated.
The O2Rotor consists of a tube/shaft with typically designed flights, to give maximum performance, clamped and bolted around the tube. Adjacent assemblies are staggered to ensure that adjacent blades do not contact the water surface at the same time. This staggering ensures the forces generated are reduced resulting in less vibration and increased bearing and gear life.
Together with a drive unit and some heavy load bearings the brush aerator can be easily installed in the oxidation ditch. Depending on the requirements of our clients, several possibilities of drive unit formats are possible.
The brush aerator can be installed standing on the side walls of the ditch or hanging under a bridge which also directly gives protection against splashing.
In some cases it will be necessary to improve the performance of the flow and oxygen transfer, for example because of the depth of the ditch. By the use of flow baffles we can overcome this.
The use of splash covers will give extra protection for the surrounding area, reduce noise and aerosols and protect the rotor from ice when the temperature drops below zero degrees Celcius.
O2Rotor aerators cover the following range:
Motor power: up to 55kW
Standard O2 transfer rate up to 90kgO2/h
Rotor diameter: 700 or 1000mm
Tank(oxid. ditch) width: up to 9m
Tank depth: 3 to 5m
Accessories which can be added to the brush aerator
O2Rotor in bridge construction