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Jet aeration – submerged wastewater aeration
Jet Aeration history
Jet aerators or educators have been utilized for gas/liquid contacting and mixing for over hundred years. This technique can be classified under the subsurface aeration systems. Over the past decades, jet aeration has become widely accepted, and increasingly popular in waste water treatment technology. Since 2006 the KLa Systems aerators we are implementing, are provided with a Slot Injector™ aeration system. This unique, innovative, high efficiency jet aeration system has been used wordwide in various industrial areas such as food and beverage, pulp and paper, chemical processing, and landfill treatment operations.
Operating Principals of traditional jet aerators
Submerged jet aeration intermixes air with a motive liquid and injects the stream into the waste water. The aerator itself consists of two jet nozzles. The motive liquid – recirculated mixed liquor – is discharged from an inner nozzle into an outer mixing nozzle, within wich compressed atmospheric air is introduced and sheared into tiny bubbles wich are entrained in the motive liquid stream.
As the stream is discharged into the surrounding mixed liquor, it forms a highly turbulent jet plume. The plume entrains the surrounding mixed liquor and brings it into contact with the tiny air bubbles. The resultant oxygen transfer rate is extremely high. This efficiency is due to the high air/waste interface area created by the minuscule bubbles, the turbulence within the jet plume, and the extended bubble residence time.
Slot Injector Aeration Technology
Introduced in 1979 by Bayer AG, the Slot Injector aerator is similar to a modern jet aerator, but uses a slot-shaped configuration to achieve higher efficiencies. The slot-shaped nozzle and mixing chamber provide a greater shear surface for mass transfer than a circular jet opening of identical area.
The unique shape of the Slot Injector results in a high percentage of gas dissolution and superior mass transfer rates.
Complete System Solutions
A typical Slot Injector™ system consists of the Slot Injector aerators, in-basin piping system, back-flush system, liquid recirculation pumps, and air blowers. The pumps are either end suction centrifugal, submersible, or self-priming. Low pressure air is delivered by positive displacement blowers, screw compressors, multi-stage centrifugal blowers, or high speed turbo blowers. Other available components of the Slot Injector™ system included with the out-of-basin air and liquid piping system consists of stainless steel pipe, isolation valves, expansion bellows, supports, and pressure gauges. Additional scope of supply is available upon request.
Water Environment Research Foundation studies show that fine-pore diffusers have reduced oxygen transfer performance and increased pressure requirements over time due to clogging, and the biggest drop-off is in the first 24 months of operation. It is not uncommon for these types of aeration systems to require frequent cleaning and replacement within the first 5 years of operation. This is not the case with Slot Injector™ systems due to much larger openings and self-cleaning capabilities, which allows for cleaning out the injectors without the need to drain or enter the basin. Back-flushing the Slot Injector system is conducted essentially with an airlift pump that reverses the flow through the inner injector nozzle resulting in a powerful air-liquid stream that clears trash and debris from the system. Slot Injector aeration systems are known for longterm, reliable operation.
Typical Jet Aeration configuration.
We can assist industries to meet the challenges of production expansion and/or optimizing energy usage in their wastewater treatment facility. Our Slot Injector™ system can easily retrofit all types of diffuser systems, including conventional jet aeration systems, within existing tanks/basins. Higher (15-60%) oxygen transfer rates can be achieved using the existing compressed air delivery components or the same oxygen demand can be met with less air flow. Slot Injector aeration also provides a more diverse operating range at peak efficiency for seasonal loads without sacrificing process mixing. We encourage you to let us take a look at your existing aeration system details and propose an economical retrofit solution using our Slot Injector™ system.
Features and Benefits of the jet aeration with slot injector
The Slot Injector™ system is a superior jet aeration system that is specifically applied to industrial biological treatment processes where fine screening is a standard pretreatment operation in both conventional and advanced air activated sludge applications. Industries that can benefit from using Slot Injector technology include : Food and Beverage Processing, Pulp and Paper, Chemical Processing, Pharmaceutical, Refinery, Textile, and Leachate Treatment.
Capital and Energy Savings
The propulsion jet of the Slot Injector aerator creates a zone of extreme negative pressure which enhances gas entrainment. Its mixing chamber incorporates a pressure recovery zone that distinguishes it from a conventional jet aerator. The result is a device that can dissolve large quantities of gas with significantly less motive liquid pumping. Like a conventional jet aerator, the hydrodynamic conditions within the Slot Injector aerator and the high energy discharge plume produce continuous surface renewal at the gas/liquid interface resulting in higher alpha factors than conventional diffusers. Compared to conventional jet aeration technology, the Slot Injector system offers some unique benefits :
Up to 60% reduction in liquid flow results in smaller and/or fewer pumps, as well as a significant reduction in the size of the liquid piping system both inside and outside the aeration basin.
The improved gas dissolution results in a 15% reduction in the volume of air required, leading to smaller blowers, motors, and/or piping systems.
The higher velocity jet plume allows for raising the Slot Injectors off the aeration basin floor resulting in energy savings due to lower blower pressure.
The higher pressure pumping system often results in a 15% improvement in hydraulic efficiency.
KLa’s Slot Injector design database along with the higher pressure pumping system allows for optimizing aeration efficiency by varying both the air and liquid flow, concurrently meeting all the basic mixing requirements of the process.
Computational Fluid Dynamic analysis of Slot Injector system aerator flow patterns in Tower Biology.
Comparative diagram Slot Injector system aerator versus conventional jet aerator system performance.
KLA jet aeration technology is applicable across a wide range of wastewater and biosolids treatment applications including: Air Activated Sludge, SBR (Sequencing Batch Reactor), MBR (Membrane Bioreactor Systems), CLR (Closed Loop Reactor), MBBR (Moving Bed Biofilm Reactor), Oxidation Ditch, Aerated Stabilization Basins, Equalization Tanks, Aerobic Digesters and Autothermal thermophilic aerobic digestion (ATAD).
Jet Aeration in wastewater treatment
Submerged jet aeration systems have traditionally been designed with their nozzles discharged horizontally, usually no more than 30 cm/one foot off the reactor basin floor. Consequently, air blowers are required to operate against static pressure nearly equal to the basin’s total depth.
The actual Jet Aeration Sytems are designed to be mounted higher, usually 75 cm to 120 cm /2 1/2 to 4 feet above the basin floor. By mounting the nozzles at this higher level, significant savings in blower horsepower can be realized, thus cutting power costs.
The jet nozzles do not discharge horizontally, like traditional systems, but at a downward angle of 15 to 30 degrees, depending on the basin’s geometry. In most applications, this system is superior in performance, compared to horizontal systems mounted 60 cm/two feet deeper in the reactor basin.
Submerged aeration system for wastewater treatment applications with Jet aeration systems : overal advantages
- Low Installed Cost
- Low Energy Cost
- Low Maintenance Cost
- High oxygen transfer efficiency
- Longterm and stable efficiency – Proven 20+ Years Design Life
- Superior mixing capacities, without extra mixing and without extra oxygen supply (anoxic periods)
- No aerosols
- No pre-cooling of the aerated liquid
- Frost unsensitive
- Low foam formation sensitivity
- No moving parts in the aeration basins
- Very suitable for use in deep aeration basins
- Obstruction unsensitive
- Reduced Off-gas Volume
- Superior Process Performance
- Superior Corrosion and Abrasion Resistance (corrosion resistant material use in the aeration basins – FRP/SS)
Other aerators :
- fixed slow turning surface aerators
- flotating slow turning surface aerators
Task has ample experience in this matter in several industrial projects.