Energy Efficient | High Alpha Factor | Low Maintenance | No Icing Problems | Deep Tank Operation | Proven Performance | High Toxicity Removal | Independent Control | Low Effluent AOX Levels | Optional Backflush | Specialization
Jet aeration systems use less energy than other diffused aeration systems. In actual wastewater treatment plants, side-by-side comparisons have shown energy reductions of up to forty percent. Figures are similar when compared with pure oxygen or mechanical aeration systems.
Jet aerators have replaced low and high speed aerators at several installations. Lower operating power and lower maintenance costs have been the reason for all replacements.
Alpha factor is the ratio of the oxygen transfer rate in wastewater to the oxygen transfer rate in clean water. Alpha factor is dependent on the aeration device used and also on the presence of chemicals such as surfactants in the wastewater.
Jet aerators produce a high alpha factor in pulp and paper mill wastes. The high alpha factor is due to the presence of surfactants in pulp and paper wastewater.
Oxygen transfer is enhanced due to the high shear at the gas/liquid interface. Typical alpha factors achieved with various aeration devices are shown below.
| Alpha Factor for Various Devices | |
| Jet Aerators | 0.9 |
| Coarse Bubble Diffusers | 0.8 |
| Fine Bubble Diffusers (Membrane of ceramic) |
0.4 |
| Surface Aerators | 0.85 |
High shear aeration devices such as jet aerators yield a higher alpha factor due to surface renewal at the gas/liquid interface. Low shear aeration devices such as fine bubble diffusers (membrane or ceramic) yield a lower alpha factor because of insufficient renewal (oxygen saturation) at the gas/liquid interface.
All aeration systems are standardized for performance at standard conditions. Therefore, the process oxygen (AOR) is converted to standard oxygen (SOR) and is inversely proportional to the alpha factor. For this reason aeration systems with low alpha factors must be designed for a higher SOR.
| Relative Oxygen Required (SOR) | |
| Jet Aerators | 100% |
| Coarse Bubble Diffusers | 112% |
| Fine Bubble Diffusers (Membrane of ceramic) |
225% |
| Surface Aerators | 106% |
A jet aeration system by Mixing Systems, Inc. consists of quality components that have an established reputation for reliability.
- Materials of construction are durable and resistant to abrasion, corrosion, and ultraviolet light.
- The jet nozzles used by Mixing Systems, Inc. have no moving parts that can wear out and no small passages to clog.
- Pumps and blowers are normally placed outside the tanks where they can be easily serviced.
In addition, the system is designed and manufactured to minimize field installation labor. Jet assemblies and piping are typically fiberglass which is lightweight, adaptable and easily installed.
All aeration and mixing occur below the surface so there is no mist or spray problems. In addition, no icing problems occur because the aeration and mixing units eliminate thermal stratification, thus preventing freezing.
Jet aerators have been used in tanks with 13 to 65 ft (4 to 20 meters) liquid depth. In deep tanks, due to the hydrostatic pressure of the bubbles, the initial and average bubble size is smaller than in shallow tanks. Smaller bubbles result in high mass transfer due to the following reasons:
- Higher surface area in the tank volume.
- The bubble stays in the tank longer due to the lower velocity of the rise.
- Higher pressure in the bubbles produce a greater driving force for oxygen transfer.
Mixing in deep tanks is provided from the bottom of the tank to the top. For this reason, jet aerators are not limited to just shallow tanks. The jet aerators provide maximum mixing near the bottom of the tank.
Jet aerators have been used in over one hundred pulp and paper mills. Jet aeration is a prevailing, proven technology that achieves high oxygen transfer efficiencies with minimum maintenance and minimum operator attention.
Jet aeration systems are designed for a twenty year life. These systems are designed so there is no need to drain the tanks for maintenance purposes. The pumps and blowers, which are generally the only components that require maintenance, are placed outside the tanks.
Jet aerators have been used in over one hundred pulp and paper mills. Jet aeration is a prevailing, proven technology that achieves high oxygen transfer efficiencies with minimum maintenance and minimum operator attention.
Jet aeration systems are designed for a twenty year life. These systems are designed so there is no need to drain the tanks for maintenance purposes. The pumps and blowers, which are generally the only components that require maintenance, are placed outside the tanks.
With the jet aeration system, both mixing and oxygen transfer can be independently controlled. Mixing is regulated by the recirculation pump. The level of oxygen transfer is controlled by the amount of air the blower releases to the jet aeration system.
Efficient mixing and oxygen transfer will yield an effluent which is non-toxic. When the wastewater is properly treated, 100% fish survival will occur in 100% effluent.
AOX (adsorbable organic halogens) are formed by a chemical reaction from the pulp bleaching processes which use chlorine or chlorine dioxide as bleaching agents. Jet aeration systems produce acceptable AOX levels in the effluent. Efficient mixing results in low AOX effluent.
A pneumatic backflush system can virtually eliminate all in-basin maintenance and manual cleaning, thereby maintaining high oxygen transfer rates and efficiencies.
By simply shutting off the pump, opening the backflush valve and continuing to supply air to the system, the unit’s aerodynamic design converts the submerged aeration system into a pneumatic air lift pump.
In the backflush mode, air flow blows backward through the system, displacing the liquid in the liquid distribution line and pumping the surrounding liquid in the reverse direction through the jets and liquid lines. This cleans the jet nozzles and the submerged aeration system of fouling material and debris. Most plants backflush their aeration tank once each month to maintain maximum efficiency.
Effluent treatment is one of the chief concerns of pulp and paper mills. Pulp mills need to efficiently produce pulp as well as treat the effluent at a reasonable cost. Typical BOD5 (biochemical oxygen demand) concentrations from pulp mills range from 100 to 5,000 ppm BOD5. In addition, this wastewater is toxic to fish, low in dissolved oxygen levels, and usually hot. Prior to discharge, wastewater needs to be neutralized, oxygenated and cooled to properly control the organics in the wastewater.
Jet aeration systems use a combination of pumps and blowers to provide efficient oxygen transfer and mixing. Jet aeration systems efficiently treat pulp and paper mill wastewater while requiring little maintenance. For these reasons, jet aerators are often considered the best method of treating wastewater for pulp and paper mills.
Jet aerators use the ejector method of contacting gases and liquids. The jet consists of a double nozzle arrangement. Each jet has a primary nozzle, an intermediate high shear mixing chamber, and an outer secondary nozzle.
Mixed liquor, recirculated from the tank, moves through the primary inner nozzle where it becomes a high velocity, low pressure stream.
Low pressure gas enters the mixing chamber perpendicularly to the high velocity liquid stream. Intense contacting and mixing of the two streams occurs in the high shear mixing chamber. The intimate contact between gas and liquid streams results in the formation of micron-size bubbles.
The fine bubble gas/liquid mist jets out through the secondary nozzle into the main tank volume. The high velocity plume from the secondary nozzle travels horizontally, spreading throughout the tank volume before riding to the surface.
The horizontal travel of the plume maintains high pressure conditions for a longer time than conventional diffused air systems. This high pressure condition gives the gas bubbles a greater opportunity to dissolve in the liquid, increasing the oxygen transfer efficiency.
Injection of the plume into the tank volume provides all the necessary mixing energy. The expanding plume’s powerful movement creates fine eddy currents in the surrounding liquid, thoroughly mixing the tank and keeping the MLSS solids in suspension.
High velocity gradients form within the tank volume and enhance mixing and solids suspension. The gradients are of a random nature, insuring the uniformity of the aerated liquid and the thorough suspension of solids.
When the initial horizontal momentum of the plume dissipates, it rises to the top of the liquid surface. This produces an air lift effect that further mixes the tank contents.
The jet plume also creates good molecular dispersion, sending oxygen molecules to microorganisms much faster. Such intimate mixing of reactants assures effective process operation.
MECHANICAL BENEFITS
Mixing Systems' submerged jet aeration and jet mixing systems are easier and less expensive to install than comparable diffused aeration systems. All equipment is supplied in prefabricated sections that are easily assembled using field joints or flanged connections. In addition, the jet aeration system contains no in-basin moving parts. All mechanical assemblies such as pumps and blowers are placed outside the tanks where they are easy to service. Combined with an optional pneumatic backflush designed to eliminate clogging, the systems are virtually maintenance free.
PROCESS BENEFITS
Aeration is often considered to be the heart of the effluent treatment system at most wastewater treatment plants. The correct selection of an aeration system is crucial because the operation of the aeration system requires about 80% of the total operating power cost of a waste water treatment plant.
Mixing Systems, Inc. jet aeration systems provide both environmentally conscious and cost effective operation. Built of quality components with an established reputation for reliability, Mixing Systems' jet aeration systems have shown energy reductions of up to forty percent over other aeration methods. In addition, during periods of low service demand, air flow rates can be reduced by controlling and varying the blower output. By regulating the air flow to the aeration system, oxygen transfer rates can be controlled without affecting the mixing efficiency or solids suspension and additional energy savings are achieved.