Launch Slideshow

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From Trash to Treasure

From Trash to Treasure

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    Feed points within the chlorine contact tank reduce chemical consumption; this photo shows the initial pass of the chlorine contact basin. Photos: City of Mankato

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    Mankato's water reclamation facility includes a treated-effluent transfer station, phosphorus-removal equipment, a filtration tank and chlorine contact basin, a final pump station and pipeline to supply a local electricity plant with high-quality cooling water, and a return pipeline.

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    Phosphorus is removed using a ballasted flocculation process. From there, effluent weir and collection flumes convey the water to filtration and disinfection.

Resource swap

Each party in the 20-year cooperative agreement between Mankato, Minn., and Calpine Corp. benefits from the other's contribution to meeting an overall goal.

Contributions

Calpine Corp.: $20 million to design and build a water reclamation facility at Mankato's existing wastewater treatment plant

Mankato: Operations & maintenance for 20 years at $500,000/year for a total of $20 million. (Costs will be calculated each year; when the total amounts equal $10 million the city will consider its portion paid and begin charging Calpine for water. If the city's portion is outstanding after 20 years, the bill will be considered paid and the city will begin charging Calpine.)

Minnesota Pollution Control Agency: Expedited Mankato's NPDES discharge elimination permit

Rewards

Calpine Corp.: An estimated $1.5 million/year savings on cooling water

Mankato: Elimination of $10 million in capital improvements to meet a 1 mg/l total phosphorus limit by the year 2015. Biochemical oxygen demand has dropped from 4.9 mg/l to below detection levels and total phosphorus levels have dropped to 0.35 mg/l.

Minnesota Pollution Control Agency: A framework for permitting other water reclamation facilities; phosphorus reduction of 52,000 pounds over four years.