Wastewater
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.
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.
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Treatment Plant and Adds Ground Storage Reservoir
Project Owner:
Osceola County Rural Water System
Key Experience:
- Maintaining the use of existing facilities during the construction of the new water treatment plant on the same site
- Surface resistivity aquifer testing to efficiently pinpoint high capacity wells
Key Features:
- 2,400 gpm water treatment plant for iron and manganese removal
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- 750 kW standby generator
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The existing South Phase WTP was constructed in the early 1980’s, with a self-contained aeration/detention/filtration system called an Aerelator®. The existing treatment equipment had reached the end of its useful life, and there was no way to rehab the existing equipment while maintaining treatment for the South Phase. Additionally, the existing WTP capacity was unable to meet OCRWS’s growing water demands, so OCRWS decided to construct a new South Phase WTP.
DGR Engineering (DGR) worked closely with OCRWS to design a new WTP to target iron and manganese removal from shallow groundwater source near the site. The new WTP was designed on the existing WTP site to minimize the project footprint and avoid additional land purchase. With the WTP location being highly visible just off IA Hwy. 10, OCRWS and DGR worked together to develop a design that not only met their water quality and capacity needs, but was also aesthetically pleasing. The new treatment process includes aeration, detention, and filtration using a gravity filter arrangement, and will increase OCRWS’s treatment capacity from 750 gpm to 2,400 gpm.
OCRWS also needed additional source water capacity to utilize the treatment capacity of the new WTP. DGR used a surface resistivity testing program to generate multiple snapshots of the aquifer depth and production capacity. Resistivity testing uses a line of electrical probes to quickly estimate soil characteristics, without the time and expense of test drilling. The testing provides a series of graphs like the one shown below. It allowed OCRWS to gather aquifer information on hundreds of acres of potential well sites with 3 days of field work and quickly identify the highest probability areas for high capacity wells. The results of the graphs were verified with test drilling, and two new well sites were identified in the thickest and most productive areas of the aquifer.
Increasing demands at the new WTP made additional on-site storage necessary. A 1 million-gallon glass-fused steel ground storage reservoir was constructed to accommodate these needs. The additional finished water storage on-site will also give OCRWS flexibility in how they choose to operate the facility.
The total construction cost of the new WTP project was $7.8 million, which was financed using a combination of Iowa State Revolving Fund (SRF) loan and private funding. The SRF funding package included a forgivable SRF loan for standby power generation. DGR also helped OCRWS navigate SRF’s American Iron and Steel requirements. The new improvements to South Phase water source will allow OCRWS to meet current and future water demands while providing their customers with reliable, high quality water.
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Project Owner:
City of Sheldon, IA
Key Experience:
- Maintaining the use of the existing facility during construction of the new one
- Cooperation with existing business and residences that would be affected by the location of the new facility
Key Features:
- New continuous flow sequencing
batch reactor (SBR) wastewater
treatment facility - Pretreatment including mechanical bar screen and non-mechanical grit removal
- UV disinfection
- 5.3 million gallons of waste treated daily
- 1,000 kW backup generator
- Automated systems
- New outfall and discharge location
Sheldon, Iowa is a community of 5,200 people located in the northwest corner of the state. The City’s existing wastewater treatment facility was nearing the end of its useful life and was undersized for the City’s current population. Additionally, a new National Pollution Discharge Elimination System (NPDES) permit required advancements in treatment which the old facility could not provide.
DGR Engineering (DGR) worked jointly with the City to evaluate multiple treatment alternatives which included updating the existing water treatment plant. Ultimately, the selection of sequencing batch reactor (SBR) was made, based on cost, operational flexibility and convenience. The option of modernizing the existing plant was rejected because the cost would have been nearly double that of a new facility.
The new plant, rated for 5.3 million gallons per day (MGD) peak day, doubles the capacity of its predecessor. It is adequate for future population growth as well as economical development with industrial growth potential.
Start up of the new plant took place in mid-July and old infrastructure is currently being demolished. The $9.5 million construction costs were funded with revenue bonding and tax incremental financing (TIF) and utilized City owned property adjacent to the existing facility. Cooperation with existing businesses and residences affected by the location of the new facility was essential to project success. The facility is expandable for future treatment requirements, and will serve the City’s needs for many years into the future.
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Project Owner:
Lincoln-Pipestone Rural Water System
Key Experience:
- Designed pump station for versatility with three initial discharge headers, one future discharge header, and two fill directions for the reservoirs
- Reconfigured distribution system including controls of existing facilities to accommodate replacement water source
Key Features:
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- Two 400,000-gallon glass-fused-to-steel ground storage reservoirs
- 1,620 gpm pump station
- New connection to serve the City of Edgerton
Lincoln-Pipestone Rural Water System (LPRW) serves approximately 4,500 customers, including 32 towns as bulk customers, in ten southwest Minnesota counties. Traditionally, LPRW treated water from their Holland water source using a reverse osmosis (RO) treatment process to remove nitrate in parallel with pressure filters for iron and manganese removal. When the Minnesota Pollution Control Agency notified LPRW that their RO discharge permit would be discontinued, LPRW needed to secure a replacement treatment process or replacement water source.
To fill this need, LPRW and DGR Engineering (DGR) undertook the Edgerton Pump Station, Reservoirs, and Pipeline project. The improvements allowed LPRW to replace the source capacity lost at the Holland water source with their water allocation from Lewis & Clark Regional Water System. LPRW is one of the founding members of Lewis & Clark, and LPRW’s ability to adapt to an alternative water source is a credit to the organization’s foresight and resiliency.
DGR tackled the unique challenge of fundamentally changing operations for the south half of LPRW’s system. LPRW’s original Edgerton Pump Station received water from the Holland WTP and pumped it east to serve customers and to fill the Chandler Elevated Tank. A new Edgerton Pump Station was designed to handle all of the same demands as the original Edgerton Pump Station and to pump water back toward the Holland WTP to serve territory previously upstream of the original Edgerton Pump Station.
Lewis & Clark has a metering facility for Rock County Rural Water District at the City of Magnolia, MN and agreed to sell water to LPRW from that facility. DGR designed 21 miles of 14-inch diameter PVC pipeline to deliver water from Lewis & Clark’s meter station to the new Edgerton Pump Station. The pipeline design includes provisions for a future booster station, which will be needed if LPRW purchases more water from Lewis & Clark in the future.
During preliminary planning, the City of Edgerton requested a bulk water service connection from LPRW. The pipeline was intentionally routed to pass near the city’s well building for a service connection to the city. A related project for a meter/pump station for the city service is currently under construction.
The pipeline delivers water to two 400,000-gallon, glass-fused-to-steel ground storage reservoirs at the Edgerton Pump Station site. The reservoirs provide flow equalization and improve pump station operability and reliability. Two reservoirs allow for redundancy in case one reservoir is out of service for maintenance or repairs.
The new Edgerton pump station consists of seven vertical multistage pumps which serve three separate discharge headers, and the station includes provisions for increasing the capacity in the future. Special consideration was given to the pipe and valve configuration so pumps can be used for multiple headers for redundancy. The station also is able to fill the reservoirs from the Holland WTP in case of source interruption from Lewis & Clark.
DGR worked closely with LPRW to incorporate preferences for station layout, pump size selection, and station capability options. DGR designed the control system and worked with multiple SCADA providers to coordinate control integration for the new facility and for communications with other water systems.
Total construction cost of the pump station, reservoirs, and pipeline project was $5.1 million, which was financed using a combination of USDA Rural Development loan and Minnesota Public Facilities Authority Point Source Implementation Grant (PSIG) funding. DGR worked with LPRW to secure funding and administer state prevailing wage requirements dictated by the PSIG funding. The new Edgerton Pump Station will allow LPRW to meet current and future water demands and provide their customers with reliable, high quality water.
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Orange City Prepares for the Future
Addition of mechanical treatment facility meets capacity and compliance
Project Owner:
City of Orange City, IA
Key Features:
- New flow-through sequencing batch reactor (SBR) wastewater treatment facility
- Preliminary treatment includes spiral screening and grit removal
- UV disinfection
The City of Orange City, IA, population approximately 6,000, received an Administrative Consent Order from the Iowa Department of Natural Resources for effluent ammonia violations of their National Pollution Discharge Elimination (NPDES) permit in 2015. The City was required to make improvements to their wastewater treatment plant to bring them into compliance with effluent limits. In turn, the City evaluated treatment options to not only meet existing permit limits, but also to comply with anticipated future limits including provisions for the Iowa Nutrient Reduction Strategy.
DGR Engineering (DGR) worked with the City to evaluate alternatives, which included constructing a sequencing batch reactor (SBR), mixed bed biofilm reactor (MBBR), retention and land application, activated sludge, or submerged attached growth reactor (SAGR).
The evaluation considered capital costs, long-term operation and maintenance costs, operational flexibility and expandability. After consideration and numerous site visits, the City ultimately determined a flow-through style SBR system to be the preferred choice based on the selection criteria and the ability to meet anticipated permit limits.
Preliminary treatment includes a spiral screen and vortex grit removal system. An ultraviolet (UV) disinfection system was also included to meet effluent disinfection requirements. A full-plant supervisory control and data acquisition (SCADA) system was incorporated in the project for remote monitoring.
The existing facility consisted of a six cell aerated lagoon system which included an industrial pretreatment cell with surface aerators, three aerated cells with diffused air, along with two quiescent cells.
The new system will utilize two of the existing lagoon cells’ flow equalization and sludge storage prior to land application. During peak flow events, the facility can split flow to utilize the dedicated lagoon for equalization and then send back influent wastewater through the plant when flows subside.
The facility was designed to treat a total flow of 2.45 million gallons per day (MGD) to accommodate projected 20-year domestic and industrial growth.
The new facility was designed for an increased population of 6,500. The improvements made the facility easily expandable for future needs and was designed with impending nutrient limits in mind.
Due to the complexity of the new facility, the required operator certification increased from a Grade II to a Grade IV certification. DGR Engineering worked closely with the City and IDNR to determine a pathway for expedited training and certification of existing staff.
Total project cost was $9.9 Million. The City used local bonds for the project costs.
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