STATIC TUBULAR AERATORS

Description

A static tubular aerator is constructed of a vertically mounted tube of 200-450 mm diameter, secured about 200 mm above the floor of an aeration tank. Air is introduced from a large diameter orifice in a horizontal air delivery pipe attached to the floor of the tank.

The static tubular aerator may be divided into two by a helical baffle pitched at a carefully calculated angle. When air is blown through the aerator, a mixture of wastewater and air spirals upwards. The flow is highly turbulent; oxygen transfer takes place within the aerator, and also beyond the unit.

Alternatively, counter-rotating turbines may be located within the tube so that the air is divided into smaller bubbles within the rising column of water. In a third type a central vertical pipe delivers air down to a ring diffuser located near the base of the vertical tubular unit.

Application

Static tubular aerators are typically used for the aeration and mixing of high strength wastewater. Static tubular aerators have application in aerated lagoons for industrial wastewaters, for secondary and tertiary treatment, pre-aeration, sludge mixing, destratification and pH balancing. They have been successfully installed for the treatment of food industry wastewaters including milk and dairy products manufacture, and in sugar refining, particularly where long process retention times are employed to handle extreme load fluctuations. Static tubular aerators are able to mix and treat wastewaters with high suspended solids.

Sizing

Static tubular aerators may be installed at depths of 3-10 m. The airflow may be varied over a range of about 3:1 and this allows the process to respond to variations in pollutant loads and save energy. Typical helical aerators have a design airflow between 20-80 m3/hour per aerator. Models with air diffusers can be made in a range of sizes passing up to 3000 m3/hour. Static tube aerators would typically transfer 10-25 % of the oxygen into solution at an electrical efficiency of 1-2 kg O2/kWh depending upon the oxygen requirement of the wastewater to be treated, and the size, number and immersion depth of the aerators. The aerators themselves are not powered, but installed air blower power may range from 05 kW to 75 kW per aerator.

An installation of 100 helical aerators providing an oxygen transfer rate of 200 kg/hour in a 5 m deep tank of wastewater would require a total air flow of about 5000 m3/hour. The electrical rating of such a system would be about 120 kW, and the electrical efficiency would be about 17 kg O2/kWh.