Lagoon upgrades achieve long-term cold water ammonia compliance

Project Background & Challenges

Kingsley, population of 1,411 residents in 2020, is located 193 miles northwest of Iowa’s capital city, Des Moines, and is best known as the hometown of Herbert Hoover, the 31st President of the United States.

Between 2000 and 2010, Kingsley saw its population grow 13.3%, compared to the state-wide population growth rate of 4.1% in the same period. At that time, the wastewater generated by the town was treated in a lagoon-based treatment plant consisting of two aerated cells and a UV disinfection system. Preparing for future growth, Kingsley realized the existing wastewater treatment facility would not meet its upcoming Iowa Department of Natural Resources (DNR) permits with stringent discharge limits, especially during the winter.


The Nexom Solution

Kingsley sought Nexom’s expertise for retrofitting the existing plant with its SAGR® submerged attached-growth reactor, a successful technology for meeting stringent ammonia limits (<1mg/L), especially during extended periods of cold weather. Nexom’s SAGR also provides polishing for cBOD5, TSS, and effluent disinfection.

Prior to the start of Kingsley’s wastewater facility upgrades in 2012, Nexom’s SAGR was not yet listed in the Iowa Wastewater Facilities Design Standards. As a result, an extensive evaluation of SAGR performance was carried out by the Iowa DNR, the town of Kingsley and their consultant, based on data presented by Nexom (still named Nelson Environmental Inc at the time). Due to the proven SAGR results, Kingsley was authorized by the IDNR to move forward with the upgrades on its wastewater treatment facility.

Upgrading the existing lagoons with optAER®

Under the new plant configuration, the two aerated lagoons preceding the SAGR were not required to meet Iowa chapter 13C guidelines for lagoon design. However, they needed to meet minimum levels of TSS and cBOD5 removal for the SAGR influent. Thus, the existing lagoons were upgraded with Nexom’s optAER® fine-bubble lagoon aeration, a technology that helps lagoon-based systems improve TSS and cBOD5 removal with minimal energy requirements, without constructing additional lagoons. In comparison with coarse bubbles, fine bubbles provide the lagoons with higher oxygen transfer efficiency because the bubbles both rise more slowly and by providing significantly higher surface area (through which oxygen can dissolve into the water) per volume of air.

The existing aerated lagoons were converted into two partial mix optAER aerated cells, with the second cell divided into a partial mix aerated zone, and an unaerated settling zone (isolated by a baffle curtain).

Implementing SAGR® post-lagoon cold water nitrification

Nexom’s innovative SAGR technology offers lagoon-based systems the exclusive opportunity to operate during long and severe cold weather, while consistently meeting the most stringent limits for ammonia in North America. In the SAGR, the water flows horizontally through a clean stone bed fully aerated that serves as media for biomass attachment. Although water may reach temperatures lower than 0.5°C (<32.9°F) in the winter, a layer of insulating wood chips or mulch at the surface prevents ice formation in the bed, which is key for successful cold water nitrification. The SAGR’s proven success is also due to Nexom’s exclusive and patented step-feed, an operation strategy that allows nitrifying biomass to overcome competition with heterotrophs (which remove BOD) by growing additional autotrophs (which nitrifies ammonia) when the water is still warm (during autumn). It is well-known that nitrification rates decrease in winter, but the additional nitrifying biomass grown in fall allows the SAGR to perform full nitrification throughout the winter.

Project Information

Location: Kingsley, Iowa

Project Type: Municipal Wastewater treatment – ammonia removal

Completion Date: July 2013

Treatment Objectives

Design Flow:0.3 MGD annually (1400 m3/day)

Effulent ObjectivesTAN: 4.5-11.9 mg/L
cBOD5: <25 mg/L
TSS: <30 mg/L
DO: 5 mg/L



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In August of 2021, the U.S. Environmental Protection Agency (EPA) released a report from authors Faycal (Phil) Zahreddine, MSEnvEng, and Smiti Nepal, P.E, titled “Innovative Nutrient Removal Technologies: Case Studies of Intensified or Enhanced Treatment” that featured Kingsley, Iowa and its SAGR as the only lagoon-based site among five other case studies.

Zahreddine and Nepal spoke with Steve Jantz, the facility’s operator, and report that “According to the KWTF facility operator, the SAGR process is simple to operate and maintain, with minimal moving parts in the system.”

Perhaps most notably, however, is the detail they provide on how “the facility produced low effluent ammonia concentrations even during cold weather months with plant effluent daily ammonia concentrations consistently below the detection limit of 0.2 mg/l except for six days during the entire 3-year period… The daily median ammonia value was below detection limit.” Later in the report, the authors provide additional context: “This is significant given the susceptibility of nitrification to extreme cold temperatures and other factors such as the potential presence of inhibiting constituents in the facility influent. 

The report was subsequently featured in a Water Environment Federation (WEF) Webcast by the same name, with Zahreddine and Jim Horne, both of the U.S. EPA’s Office of Wastewater Management, presenting the Kingsley case study. As of July 2022, the Webcast is archived on the WEF website. 

Upgraded System Performance

Eight years later, Kingsley’s SAGR maintains compliance for ammonia, cBOD5, and TSS despite new and stricter Iowa DNR permit limits. In 2019, the Iowa DNR updated the limit for ammonia in January, lowering it from 11.9 to 9.4 mg/L, however ammonia concentration in the SAGR effluent has generally averaged well below 1 mg/L.

Kingsley observed a sharp increase in SAGR influent ammonia during the step feed period in Fall 2020. The sharp rise resulted in a brief increase in effluent ammonia compared to other years. As Nexom values client support and actively collaborates with data monitoring, our engineers advised the operator to end the step-feed process, and the success of the strategy was observed in the next samples, with effluent ammonia levels returning to <1 mg/L even as influent levels continued to rise.

In total, the SAGR has performed as expected, with >95% of samples since early 2014 showing ammonia levels below the tests’ detection levels. Even assuming ammonia levels for those samples were right at the minimum detection level, the SAGR has produced an average effluent ammonia of <0.5 mg/L.