Aeration for industrial and municipal wastewater treatment involves more than simply moving volumes of air through a treatment basin. It really comes down to creating and sustaining an optimal oxygenated environment for microorganisms to convert waste matter into CO2 and water. Here are some key considerations for making better retrofit decisions about upgrading existing basin capacity and efficiency with jet aeration.
Why Upgrade?
The reasons for retrofitting wastewater treatment basins can differ across a range of industrial and municipal applications. If the following issues are concerns, it could pay to investigate not only a retrofit in hardware, but a retrofit in the aeration technique itself:
- Aging or worn-out equipment, especially in harsh or caustic industrial environments, can require frequent cleaning and sometimes even complete replacement in as little as five years. Instead of simply replacing worn aeration headers with the same design, upgrading to jet aeration or slot aeration with wear-resistant nozzles can improve throughput efficiency and system longevity within the same space. Some jet aeration systems designed to last 20 years under water are still operating 30 years after installation.
- Demands for greater treatment capacity can come from expanding production capacity in industrial applications or from regional growth in municipal applications. In either case, the path of least resistance might be to satisfy the upgraded application requirements with minimal disruption to existing operations. Being able to boost capacity without requiring the time and investment of installing new treatment tanks or basins can be a powerful motivator.
- Challenging industrial wastewater composition is another potential driver for upgrading wastewater treatment. These upgrades can take place at in-house industrial plant facilities, or at municipal wastewater treatment plants (WWTPs) challenged by new industrial customer circumstances.
- Soaring energy costs can also be the motivation for exploring new, more efficient aeration technology. Jet aeration systems deliver better oxygen transfer rates than other aeration options, along with lower combined energy requirements for blowers and pumps (Figure 1). Slot Injector ™ systems offer a better turn-down ratio — 30 percent reduction in flow and 60 percent reduction in pump energy savings — to decrease energy consumption at periods of lower demand. With smaller pumps, piping, and valves, they also require less capital investment than traditional jet aeration.
Figure 1. Jet aeration uses a combination of low-pressure air and pumped liquid to generate a horizontal jet plume of air and liquid to mix and oxygenate wastewater in an aeration basin.
- Environmental concerns, such as mechanical aerators creating unhealthy aerosols in a wastewater environment, are yet another potential reason for upgrading. In refinery wastewater treatment environments, these aerosols are often seen as oily coatings on the ground or walkways.
Achieving More In Challenging Environments
With high mixed-liquor suspended solids (MLSS) loads — often 1,000 to 3,000 mg/L, and sometimes as high as 30,000 or 50,000 mg/L in food or beverage applications — industrial wastewater challenges are typically far more challenging than municipal wastewater’s MLSS of 100 to 200 mg/L. With a lower frequency of clogging and excellent oxygen transfer efficiency, jet aeration is well suited to applications with heavy biochemical oxygen demand (BOD) — e.g., dairy, distillery, pork, poultry, etc. It even retains excellent oxygen transfer performance in the presence of surfactants and anti-foaming and cleaning agents found in pharmaceutical, textile, and papermaking facilities.
Achieving More In An Existing Footprint
Whether an aeration process upgrade is being planned due to the age of the current treatment facility or a need for changes in the biological treatment processes, jet aeration — with or without slot injectors — is an attractive space-saving alternative. It enables users to increase wastewater treatment capacity within an existing basin footprint and avoid the costs of a new, larger aeration basin or new blower equipment. Skid-mounted systems even make it easier to install a new jet aeration system in an existing basin without having to drain it.
- Using Physics To Greater Advantage. How oxygen is introduced into the aeration basin, the impact of a liquid jet stream on mixing, and the resulting exposure time/efficiency at which oxygen transfers to the mixed liquor are important factors for aeration performance (Figure 2). The overall mass transfer coefficient discussion in this guide provides a good understanding of how that process works and the impacts of varying wastewater characteristics on it.
Figure 2. The plume of liquid and bubble emerging from a jet aeration nozzle creates a longer path and a longer time of oxygen exposure to wastewater than conventional fine-bubble or coarse-bubble diffusers.
- Benefitting From The Experience Of Others. Jet aeration and slot injector systems, which are frequently used to rescue failed aeration systems, offer hope for industries facing new challenges in capacity or chemistry. One food processor who was forced to change diffuser systems in a sequencing batch reactor (SBR) twice in a 10-year period was able to double the oxygen transfer capacity from its existing blowers by retrofitting its aeration basin with a slot injector system that was less prone to clogging.
Grooming A Path To Acceptance And Efficiency
An important consideration for success in any aeration retrofit installation is getting staff buy-in and acceptance of new technology or work procedures.
When upgrading from mechanical “splash” aeration, which is basically an on/off system, promoting staff understanding of new jet-aeration technology or work procedures is critical. This is where the operational flexibility and ease of operation for a jet aeration system can be an important benefit. Showing operators how a new jet aeration system can help them turn down or ramp up quickly and with little effort in response to changing conditions goes a long way toward achieving the desired acceptance and results.
The more extreme the wastewater applications, such as refineries, food processing, or pulp and paper production, the greater the appreciation for low-maintenance features. Pump and blower equipment that minimizes the need for oil changes or mechanical seal replacement is popular with understaffed utilities and overworked operators. Jet-aeration nozzles that use wear-resistant composite materials to tolerate high temperatures or challenging chemical environments and minimize cleaning effort and frequency can pay dividends in the long run.
Finally, leveraging the experience of suppliers with specific industry-application expertise and references makes it easier to communicate insight into problems and opportunities associated with unique wastewater aeration challenges. Ask those suppliers for examples of previously constructed retrofit systems that have solved wastewater treatment challenges like the ones faced in the targeted application.
