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Wastewater Treatment Plant
MEETING WASECA’S NEEDS NOW AND INTO THE FUTURE
Welcome to the City of Waseca Wastewater Treatment Plant.
The City of Waseca has a proven proactive environmental record to resolve wastewater system problems. In 1985 we constructed a new treatment facility to eliminate raw sewage pumping to the Minnesota River Basin; in 1995 we constructed a new municipal sludge treatment facility to comply with Federal rules; in the mid 1990’s we started an aggressive City program to reduce clean water entering the sanitary sewer system (called Inflow and Infiltration) and in 2002 the City Council adopted an ordinance to inspect all private properties in Waseca to eliminate private property storm sewer connections to the sanitary sewers.
Today, our City struggles with undersized trunk sewer mains that result in household basement flooding and occasional raw sewage entering Clear Lake, which requires Clear Lake public access closings. The Minnesota Pollution Control Agency (MPCA) has told us to resolve our wastewater system problems or sanitary sewer permits for City expansion may not be approved by the MPCA. Without such approval, our community could not grow, and this action would effectively halt economic growth. The City Council has determined that Waseca will continue to grow and be a vibrant community into the 21st century.
To this end, The City of Waseca, assisted by Bonestroo Engineering, has developed a Wastewater Facilities Plan that will improve the hydraulic capacity of the wastewater conveyance system and treatment plant, as well as implement phosphorous removal, expand capacity for additional growth within the community, enhance biosolids treatment and storage, and make general repairs and replacements of the existing facility. The engineer’s estimated cost of improvements to the City’s wastewater facilities is $ 17,180,432. We are hopeful that the project will be bid this spring, and once the contract has been accepted by the City Council the work can begin within 45 days.
Included in the $17,180,432 is the anticipated Total Daily Maximum Load (TMDL) Grant for phosphorus treatment in the amount of $736,225 from the Minnesota Public Facilities Authority. Our project is ranked number one (#1) on the State Project Priority List for wastewater construction projects. The final grant award would be based on the actual bids received and authorized by the Council, but can’t exceed the original request of $736,225.
We are submitting our application for a Public Financing Authority (PFA) bond for the remaining $16,444,207 of the construction project. Because we are number one on the project priority list we feel confident we will receive a loan, which is to be repaid for 20 years at 3% interest. The projected annual debt service payment is $1,105,309.
To meet the annual debt service payment, the City Council approved a staff recommendation to pay thirty percent (30%) of the debt service payment through a special tax levy and seventy (70%) of the debt service payment through an increase in wastewater fees. The result is a 9.54% increase in property taxes and a sixty (60%) percent increase in wastewater rates.
CURRENT SYSTEM
TREATMENT EXPECTATIONS
Treatment guidelines were established with the Clean Water Act of 1972. This federal law has required municipalities to treat sewage to a high quality in order to make all rivers and lakes fishable and swimmable.
STATE OF THE ART EQUIPMENT
The average Wasecan uses about 70 gallons of water a day. This wastewater flows through the City’s collection system for over two hours before it enters the activated sludge wastewater treatment plant.
The major structures and their functions listed in order of treatment are:
1. Pump (Lift) Station – A central collection point for all incoming wastewater (influent). Large pieces of unwanted debris are screened out here.
2. Grit Chamber – This is a settling tank for types of solids (grit), which cannot be biologically treated.
3. Blower Building – At the blower building, air is provided to the microorganisms in the basins. A standby generator is also in this building, which provides emergency electricity in case of power failure. The City contracts with Xcel Energy to shed kilowatt load during peak control periods. This allows the City to purchase power at reduced rates. This program has been in effect since 1988.
4. Activated Sludge Aeration Basins – These two basins (104 ft. wide by 14 ft. deep) are where billions of microorganisms convert the suspended wastewater solids into types of solids (sludge) that settle by gravity.
5. Final Clarifiers – These two tanks (65 ft. wide by 12 ft. deep) allow the mixed liquor from the aeration basins to separate. The top layer is effluent, which is 95% to 99% cleaner than the influent. The material that settles is sludge.
6. Static Aerator – The effluent passes over this man-made waterfall to increase the level of oxygen in the water.
7. Chlorination/Dechlorination Basins and Building – Viruses are killed by chlorine mixed into the water. Sulfur dioxide is mixed with excess chlorine and both are rendered inactive. The water is then discharged into the LeSueur River.
8. Sludge Thickening – Sludge is further concentrated by the addition of coagulants, which cause the solid particles to stick together while excess water is allowed to filter through a coarse screen.
9. First Stage ATAD – Sludge is transferred into the first of three ATAD (Autothermal Thermophilic Aerobic Digestion) reactors (18 ft. wide by 12 ft. high) and mixed by spiral aerators. Here, “heat loving” microorganisms begin to further stabilize solid particles. This process produces heat, which allows the reactor to reach approximately 50° C.
10. Second Stage ATAD – The final two ATAD reactors reach about 60° C and maximum sludge reduction takes place. This process transforms the sludge into a safe biosolid.
11. Land Application – Treated biosolids are then applied on state approved and regulated fields, located adjacent to the airport, for its crop nutrient value.
12. Laboratory/Administration Building – Water testing is done to satisfy the water quality permit and to control the activated sludge process.
13. Maintenance Building – This building houses sludge pumps and aeration equipment, which are used in sludge treatment. Equipment repairs are also performed here.
DESIGN PARAMETERS
Design Flow – 2.34 million gallons per day
Peak Flow – 5.58 million gallons per day