As industries expand, they typically need to increase the capacity of their wastewater treatment facilities. Increasingly stringent regulatory requirements, such as lower nitrogen limits, may also signal the need to boost treatment capacity. Installing additional tanks and larger equipment not only adds capital costs but increases operating costs as well.
With the evolution of the use of dissolved air and membrane solids separation systems, in many cases treatment capacity at industrial wastewater plants can be increased without adding tank volume. Aeration basins are the heart of a wastewater plant, where the biological removal of pollutants occurs. Aeration provides oxygen to the microorganisms that remove targeted pollutants from the water as well as provides the mixing required for the biological process to succeed.
Jet aeration systems transfer oxygen by simultaneously introducing large volumes of high-kinetic energy liquid and air through a series of injectors or jet nozzles. This creates intense mixing action as the gas/liquid plume flows along the floor, then vertically to the top of the basin. This provides excellent mass transfer of oxygen. Retrofitting aeration basins with jet aeration technology provides extremely efficient biological treatment. This allows the existing plant to treat additional organic loading, while meeting required effluent limits.
Retrofitting Systems With Jet Aeration
Industrial treatment plants typically have mechanical surface aerators, diffusers, or older jet aeration systems. When increasing capacity, options include removing the existing equipment and adding volume or keeping the same volume but improving treatment effectiveness. In most cases, the jet aeration system provides much better oxygen transfer and can boost treatment capacity by 60 to 100 percent in the same plant footprint.
Jet aeration systems have other advantages as well. They are much less likely to be affected by biofouling or chemical scaling. Maintenance is minimal. And there are no membranes to foul or fail.
Mechanical Aerators
Some industries can benefit by replacing mechanical surface aerators with jet aeration, especially when lower nitrogen limits are enacted. Surface aerators work by drawing water from below and flinging it into the air where oxygen is absorbed. In some plants, the evaporative cooling that occurs with this aeration method significantly lowers bulk volume temperature and negatively affects nitrification. This can result in violating nitrogen limits. Certain industries have also replaced surface aerators to avoid exposing employees to harmful aerosols.
Retrofitting aeration basins that have surface aerators requires installation of a pump and blower and installation of air piping and jets. Capacity can be greatly increased without adding tankage.
Diffused Air Systems
Diffused air systems pump compressed air through membrane-covered diffusers located on the bottom of the aeration basin. Typically, numerous diffusers cover the full floor of the tank. Oxygen transfer occurs as tiny air bubbles rise from the bottom to the top of the tank. Retrofitting these systems is very cost-effective, as existing blowers can typically be reused. Pumps need to be installed, but the air piping does not need to be reconfigured. The jet aeration design features less floor coverage. By retrofitting diffused air systems to jet aeration, a higher mixed liquor suspended solids (MLSS) can be maintained, and the oxygen transfer capacity will increase of 60 to 100 percent in the same volume without adding additional blower capacity.
If gravity clarifiers are used for solids separation, the MLSS still cannot get too high, so capacity increase is limited without adding more aeration volume. For systems using dissolved air flotation or tertiary membrane filtration, a much higher MLSS can be accommodated in the aeration basin. These systems could increase treatment capacity by up to 2 to 4 times without adding tankage.
Increased Energy Efficiency
In addition to gaining capacity, it’s possible to increase energy efficiency by retrofitting aeration basins with jet aeration. In some cases the jet aeration design can double the oxygen transfer rate. The only equipment addition is the pump, which increases power use by about 40 to 50 percent. Therefore, oxygen transfer and treatment capacity are increased by as much as 100 percent, with a power increase of only 40 to 50 percent.
An example of this occurred at an industrial facility in Indiana that retrofitted its older coarse bubble diffuser system to jet aeration. Due to the difference in alpha factor and clean water oxygen dissolution efficiency, the jet aeration system delivered 1,500 pounds of standard oxygen per hour versus the previous 800 pounds per hour using the same blower system with only 40 percent more pump power being used.
Conventional Versus Slot Injector™ Systems
Slot Injector™ systems are superior jet aeration systems that use a slot-shaped configuration to achieve even higher efficiencies. The slot injector is a lower liquid flow, high-pressure jet aerator. Slot injectors provide more than twice the liquid flow to transfer the same amount of oxygen. This lowers capital costs, as associated piping and pumps are smaller.
Slot injectors are also about 10 to 15 percent more energy efficient than conventional jet aeration systems and are now replacing many 20+-year-old conventional jet aeration systems around the world.
Failed System Rescues
Jet aeration and Slot Injector ™ systems have been used many times to rescue failed aeration systems. One example involves a food processor with a sequencing batch reactor (SBR) process that had to completely change out its diffuser systems twice in a 10-year period. When the third retrofit was required, it evaluated options and decided to retrofit the aeration basin to a Slot Injector ™ system. It now has double the oxygen transfer capacity using the same blowers.
In addition, these retrofits can be done rapidly, and sometimes without taking the tanks out of service.
Engage The Help Of A Technical Partner
Aeration systems are the most important part of a biological treatment plant. Designing a retrofit is a complex process. Jet aeration suppliers have the depth of knowledge and experience to provide a cost-saving, efficient system that can boost plant capacity without adding new tanks.
