Kansas WRRF Aeration Blower Upgrades Save 40% in Energy Costs

For Scott Millholland, Superintendent of Kill Creek Water Resource Recovery Facility, Gardner, Kansas, ongoing plant improvements ensure the best possible service.

Municipal wastewater treatment is highly technical and complicated, yet the operating strategy at Kill Creek Water Resource Recovery Facility (WRRF) in Gardner, Kansas, isn’t. That’s because the focus is to save money without sacrificing quality, all while operating safely at all times.  

To that end, the plant recorded another win in its long list of accomplishments when it replaced aging multistage blowers with high-speed integrally geared blowers in 2020. The new blowers with Variable Frequency Drive (VFD) control are credited with a 40% reduction in energy consumption for aeration. This results in an annual savings of $35,000. The blower upgrade, which also helps protect the safety of employees, is expected to deliver a payback of less than five years.

Kill Creek WRRF Superintendent Scott Millholland said it’s all about ongoing improvements and the use of advanced technology to deliver the best possible service.

“Safety is always No. 1 on our list and second is making sure the plant is performing at its best as we meet our permit limits,” said Millholland, noting energy savings plays a key role in performance. “The more energy we save, the more it increases our revenue long-term so it’s saving citizens money. That’s money we can use on future infrastructure projects.”

Energy Gains Importance

The Kill Creek facility is a Kruger Bio-denitro oxidation ditch plant. It opened in 2002 and is designed to treat an average of 2.5 Million Gallons per Day (MGD) and a peak capacity of 7.5 MGD. It serves nearly 25,000 residents.

The plant uses phased isolation ditch technology for Biological Oxygen Demand (BOD) reduction and biological nutrient removal. Major components include an influent lift station with submersible pumps; a headworks operation with a channel grinder, step-screens, and biological odor control; two rapid-sludge removal sedimentation basins; a gravity thickener basin; a Pre-Thickened Aerobic Digester (PAD) system with two digester basins; a non-contact UV disinfection system; and screw press for sludge dewatering.

Since its inception the plant has continuously implemented cost-savings measures and upgraded technology as part of its capital improvement plans. A prime example is the plant’s ability to reduce biosolids production through efficient processes and the replacement of a belt press with a screw press for dewatering. Those measures alone save the plant upwards of $60,000 per year in operating expenses. 

In 2016, the plant began evaluating ways to reduce energy consumption whether that meant changing out incandescent lightbulbs for LED lights, better insulation throughout the facility or any number of technological upgrades. 

“We went through a big change,” Millholland said. “We’re one of the biggest energy users in the entire city and we wanted to do more to conserve energy.”

Powering Airlift Pumps and Diffusers

Sludge at the plant is treated in two aeration digester basins, each measuring 51 feet by 62 feet with a depth of 21 feet. As an extension of the activated sludge process, each basin is aerated via two air diffuser headers that span the length of the digester and are equally spaced to provide even distribution of air. 

Blowers supply air to the diffusers, as well as five airlift pumps used to transfer Return Activated Sludge (RAS) to the head of the plant and Waste Activated Sludge (WAS) to the digesters. A higher focus on energy conservation drove Millholland to consider the replacement of three, 125-horsepower (hp) seven-stage blowers installed when the plant began operation.

Energy efficiency is a priority for the Kill Creek treatment plant’s aeration digesters.  

“Our blowers run 24 hours a day, seven days a week because you have to have the air for the airlift pumps,” Millholland said. “We never had any problems with our original blowers as far as maintenance, but they were on our list of equipment to be replaced and we knew they used a lot of power.”

To validate potential energy savings, the plant measured energy consumption of the multistage blowers. The assessment suggested newer technology could dramatically reduce blower energy consumption. An upgrade would also allow the plant to address noise and heat issues with the blowers, housed in an enclosed room next to the digesters. 

“Those blowers created a noise level inside that building that was up over 110 dBA. You had to wear earplugs at all times, and it made it very difficult to communicate with each other. It was loud,” Millholland said. The blowers also generated heat that would cause blower room temperatures to reach 140°F (60°C) during summer months. 

New Blowers a Perfect Fit

The Kill Creek WRRF team chose to partner with Inovair (www.inovair.com) to install new blowers in late 2019 after reviewing numerous bids. Based in Lenexa, Kansas, Inovair is a short distance from the plant.

Together, the team at the plant and Inovair opted to replace the original three blowers with three VFD, integrally geared IM-20 blowers. As with the original blowers, the IM-20 units are each designed to deliver up to 1,905 scfm at 7.5 psig – yet the new 75-hp blowers do so with much less horsepower than the original 125-hp machines.

Integrally geared Inovair IM-20 blowers help the plant save energy, while also solving heat and noise issues. 

In addition to efficiently providing air, the low-profile IM-20 blowers are well suited for applications where space is limited. The blowers, which fit through a standard 36-inch man-door, were installed in the same footprint used for the multistage blowers. Additionally, piping for the installation only needed to be slightly modified to accommodate the original inlet filters and the main discharge line.

Plant Saves $35,000 in Annual Energy Cost

Soon after the new blowers were installed, the plant measured the blowers’ electrical consumption. Millholland said he couldn’t be more pleased with efficiencies realized. 

“Each new blower pulls 45 amps, which compares with the older blowers that were each running 100 amps,” he said.  Efficient blower operation, aided by VFD capability, has allowed the plant to reduce electrical consumption for aeration by 40% for a $35,000 annual savings. Since the installation of the blowers, the plant has gone from being the No. 1 consumer of energy in the city to the third largest energy user.

Equally important as energy savings is the ability of the new blowers to deliver air to the airlift pumps and diffusers at a constant pressure of 7.2 psig, which is vital to the operation. Doing so was a challenge in the past given swings in ambient temperatures that can range from 35°F (1.6°C) to 65°F (18.3°C) in a single day. 

“When we would get big swings like that, we had to manually adjust the old blowers to maintain needed pressure,” Millholland said. 

Manual adjustments are no longer needed given VFD control on the new blowers, said Nate Neufeld, Sales Manager, Inovair. 

“When ambient temperatures are low, the speed of the blower is automatically reduced so the blower uses less power to deliver air,” Neufeld said. “Efficiencies gained translate to energy savings.”

Today, a single blower will handle the bulk of the plant load while a second automatically kicks on if and when needed to maintain pressure at 7.2 psig without fail. The third unit serves as a backup unit with all three rotated into operation on a seven-day cycle. 

The blower upgrade has eliminated other challenges related to heat, as well as noise. Now the temperature in the blower room is usually closer to ambient during summer months, which adds to the comfort level. With the noise level now below 80 dBa the blower room is also more conducive to the plant’s goals for a safe work environment. 

Existing intake filters and piping were reused, reducing installation costs for the new blowers. 

Millholland said the blower project is another example of how a focused approach with clear goals continues to benefit the Kill Creek WRRF and taxpayers. And aeration blowers, said Millholland, is something the plant won’t need to think about for a long time.

“We’re sitting in a pretty good spot,” he said. 

All photos courtesy of Inovair.

For more information on Inovair visit https://inovair.com, email: sales@inovair.com, tel: 1-855-INOVAIR

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