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An effluent fit for the affluent

North Liberty’s advanced wastewater treatment plant
Return activated sludge pumps send a high flow of biologically treated mixed liquor (a mixture of raw or settled wastewater and activated sludge) past a filtration membrane for permeate water extraction. North Liberty’s wastewater treatment plant is a pioneer in the application of membrane bioreactor (MBR) technology in the State of Iowa, which negates the need for conventional clarifying tanks and water disinfectants. (photo by Cale Stelken)

NORTH LIBERTY– It’s safe to say North Liberty’s a special place. And while the growing community maintains its small town ambiance, it certainly doesn’t cut corners. Even the city’s approach to wastewater treatment is top-notch– just ask newly appointed Superintendent Drew Lammers.
“Everybody throughout the city, residents included, should be proud of what we have,” Lammers remarked.

Plant overview

Built in 1967, North Liberty’s wastewater treatment plant underwent major upgrades in 1998 when it was a sequential batch reactor (SBR) facility.
“SBR was still a small footprint plant, but it took a lot less flow,” Lammers explained. “The plant then was running at like 120 percent capacity, and that was previous administration, previous operations crew.”
After the plant faced some violations, the City of North Liberty took on new management staff and in late 2008 converted to a membrane bioreactor (MBR) plant, the first of its kind in Iowa.
“They really got ahead of everything, and they put in what I would say is probably the best technology that you could have for treatment,” Lammers said. “It’s costly, but it’s definitely the most advanced treatment.”
The technological advancements are a welcome feature, given the city’s steady growth.
“We’re taking on everything that the currently 19,000 population takes, which down here is, on average, about 1.5 million gallons a day,” Lammers said of the city’s current water use. “If you look at this plant as a whole, it’s a fairly small footprint for the amount of flow that it takes in.”
Should a mechanical failure occur, a pump-fed, gravity-return 5.5 million gallon equalization basin, located inside a large grassy hill on the facility premises, would provide about three days of storage.
“Redundancy is huge– having multiples of things, having spare parts. Just having good preventative maintenance on equipment is key, because this stuff never shuts down,” he stressed.
The operation is maintained on standard eight-hour shifts, five days a week with an on-call operator seven days a week.
“A lot of that’s based on the technology we have these days,” the superintendent said, citing the employment of iPads and cell phones to access facility equipment. “What you see out there for infrastructure, I’ve got at my fingertips with a click of a button.” 

An innovative process

Membrane bioreactor treatment consists of three basic treatment stages: pretreatment, secondary treatment and digestion.
As the city sewage lines bring waste in, it passes through a bar screen to filter out rocks, sticks and other debris before a second screen removes sand, rocks and inert material.
“That screen picks up anything human-size hair and up,” Lammers noted.
This keeps the organics in the wastewater and removes all heavy, foreign debris, which is then washed, dried and put into dumpsters.
Nutrient reduction, the elimination of nitrogen and phosphorous, is an important part of modern wastewater treatment, as the elements can travel from Iowa to the Gulf of Mexico hypoxia (an oxygen depleted area) and form toxic algae blooms.
To prevent this, microbes are used to degrade the pollutants. However, as opposed to the more conventional SBR method, which relies on clarifying tanks, the biologically-treated mixed liquor (a mixture of raw or settled wastewater and activated sludge) then passes through submerged membranes, filtering out water and a leaving a thicker solid behind. Air is introduced through integral diffusers to continually scour membrane surfaces during filtration, facilitate mixing and contributing oxygen.
This filtration transforms the water into fishable, swimmable effluent, which is then discharged into Muddy Creek and heads into the Iowa River.
“It produces a far, far superior effluent than any other wastewater treatment plant out there,” Lammers said, citing that, while the drinking water standards requires a content limit of .3 NTU (Turbidity Value) or less, “our water a lot of times is .03, so we’re 10 times than what the standard is for drinking water. That falls under ultrafiltration.”
The membranes feature small enough porous openings that North Liberty’s facility is not required to apply disinfectant or add any chemicals as a conventional plant would.
“It truly is an advanced technology for wastewater treatment,” Lammers remarked.
The separated solids enter the digestion process, to condition into biosolids. A contractor hauls the fertilizer, a Class B biosolid, to local farm fields, with the plant rotating fields on a five-year plan.
“We provide it as basically a benefit to the local farmers,” Lammers said. “We’ve had people as far south as Keokuk come up and they were interested in our product.”


North Liberty’s wastewater plant underwent ambitious expansion beginning in July 2015, with finalization anticipated in May or June.
“I’ve learned the plant from absolutely not knowing anything about this, to knowing all the details through as it was before this plant expansion,” Lammers recalled. “I was an operations supervisor when we started the design and planning of this plant expansion, which gave me the ability to be a part of that management team.”
A dewatering press was a major feature of the expansion. This removes water from the digested sludge and creates a dry fertilizer.
“That dewatering has been a great tool,” Lammers said, comparing the transportation costs of wet and dry byproduct. “It’s proved itself very cost efficient, and it’s gonna have a good return of investment.”
The fertilizer is placed in a dry storage building, while the expelled water returns to beginning of the plant to undergo treatment again.
“I think we’ve made some good steps to providing good public service,” he said of additional improvements. These include an activated carbon control unit for pretreatment odor control, as well as silencers on all blowers to reduce noise.
“It’s more beneficial long term for the whole community, especially with our location,” he added, noting the plant’s close proximity to North Central Junior High and Coralville residencies.
During expansion, the plant scaled down from three to two digesters, but introduced new screens, upgraded lift pumps to increase capacity and a new style of aeration membrane that’s 30 percent more efficient. The new membranes have the potential to take on seven million gallons of water a day. And while they have a 10-year life expectancy, with preventative maintenance, Lammers hopes to push them farther.
On a local level, North Liberty’s treatment facility has been a pioneer of MBR technology; the plant is part of a General Electric users group focused on membranes, to which it has contributed insight; North Liberty has also been approached by other local governments interested in transitioning to MBR.
While wastewater may not be the most popular municipal subject, the young, six-member staff at North Liberty’s treatment plant makes an effort to spread awareness on the function and necessity of efficient wastewater treatment. The team has given presentations at schools during science and engineering classes, and Lammers serves as regional director for the Iowa Water Environmental Association (IAWEA), where he helps organize annual meetings and trains operators.
“It’s not really a topic of discussion, wastewater, but we like to be educators down there and educate the residents and certainly all of you whenever questions come about,” Lammers said during his city council appointment to superintendent. “Even if it is the question of whether it’s legal or not to flush a fish.”