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Dawn VanDenTop

Wastewater Treatment Facility

July 25, 2022

Wastewater Treatment Facility


Schleswig Wastewater Treatment Facility Moves Out of Town

Schleswig had two major decisions to make:
what type of treatment technology to construct,
and where it should be constructed.

Project Owner:
City of Schleswig, IA

Key Experience:

  • Selecting a suitable site for a new treatment plant involved coordination with:
    - Local landowners willing to sell land for a reasonable cost
    - County engineers to provide improved site access on minimum maintenance roads
    - Electrical utilities to provide new electrical service to the site
  • Schleswig received funding through the WWDWTFAP in the first year it was signed into legislation; a total of $775,000 in grant was awarded to six projects in Iowa in the first year

Key Features:

  • New WWTF designed to treat:
    - Average wet weather (AWW) flow
    of 0.234 million gallons per day (MGD)
    - BOD load of 276 lbs/day
    - Total Kjeldahl Nitrogen (TKN) load
    of 58 lbs/day
  • Total construction cost of $3.5 million. The project was financed through:
    - SRF loan program including
    Planning & Design Loan
    - $300,000 CDBG grant
    - $100,000 Wastewater and Drinking Water Treatment Financial Assistance Program (WWDWTFAP) grant

The City of Schleswig, Iowa is a small, German-heritage town located just north of Denison on U.S. Highway 59. To treat its wastewater the City operated a 3-cell aerated lagoon facility located in the south part of town that was originally built in 1960, with upgrades made in 1975 and 1999. Since its construction, the community has continued to expand around the treatment facility, including a golf course directly to the west and a residential housing development immediately south. Each spring as the ice would melt, the lagoons would turn over and create an odor issue throughout town, while the floating aerators provided a constant humming sound as background noise to any activities taking place near the facility.

In 2017 the City was issued a new NPDES discharge permit which contained more stringent ammonia limits as well as new E. coli limits. Similar to many small communities in Iowa, Schleswig’s aging lagoon treatment facility could not meet these new limits. It was clear that innovation was needed; hence, the City retained DGR Engineering (DGR) and began planning a wastewater treatment facility (WWTF) improvements project.

In modifying their WWTF, the City had two major decisions to make: what type of treatment technology to construct, and where it should be constructed. With input and advice from DGR, the City decided that the best option would be to build a LemTec ™ treatment system, and to move it out of town.

The City was able to purchase 7.35 acres located 2.5 miles east of town to build its new treatment facility. The LemTec™ system was chosen based on its relatively small footprint, ease of operation, and low capital and operation and maintenance costs. Ultimately, the LemTec™ system allowed Schleswig to meet the more stringent permit limits utilizing a robust, easy-to-operate, affordable technology.

The project included a new inlet screening building with a vertical mechanical screw screen and compaction system intended to remove, wash, and compact solids in the wastewater stream larger than 0.25 inches. The screening system is followed by a duplex submersible pump lift station, both located at the existing treatment site. The lift station pumps the screened influent through 2.5 miles of 8” forcemain to the new treatment site.

Wastewater graphic

Many WWTFs that struggle to meet ammonia limits have more issues in the cold winter months than in the summer. This is because at a wastewater temperature of 60°F, the nitrification rate at which bacteria treat ammonia begins to decline, and at a wastewater temperature of 50°F the treatment efficiency is reduced by half.

The LemTec™ system helps combat this phenomenon in two ways: first, the insulated lagoon covers help retain heat in the system; second, the fixed media in the polishing reactors provides greater surface area to allow a larger population of nitrifying bacteria to grow and treat ammonia.

The LemTec™ system at the new treatment site consists of two aerated treatment lagoons which are covered with insulated, floating covers to retain heat and increase treatment efficiency.

The aerated lagoons are followed by small polishing reactors which contain fixed media to provide additional ammonia treatment. Effluent from the polishing reactors is disinfected through a UV disinfection system for treatment of E. coli prior to discharge to the receiving stream.

The system began initial start-up in mid-December 2021, and after a slow start-up process due to a cold winter and spring, is currently treating the wastewater to non-detectable ammonia concentrations (< 0.5 mg/L).

The City is currently working on filling in one of the old treatment lagoons, and the floating aerators and baffles were removed from the other treatment lagoon as a part of this project. A walking trail winds past the old treatment lagoon, and now instead of nuisance odors and loud humming from the floating aerators, residents can enjoy a serene view of a pleasant, quiet water feature while their wastewater is being effectively treated outside of town.