The city of Mankato, Minn., in partnership with Calpine Corporation and Black & Veatch, has earned the 2007 Project of the Year Award in the Environment category (for projects greater than $10 million) from the Minnesota chapter of the American Public Works Association (APWA) for an environmentally and economically beneficial water reclamation facility (WRF).
The facility produces high-quality water for reuse in the generation of electricity by Calpine. It is the first of its kind in Minnesota and one of the first in the United States.
Black & Veatch provided planning, design and construction-related services for the facility, which was constructed through a three-way public-private partnership among Mankato, California-based Calpine and the Minnesota Pollution Control Agency (MPCA).
The city owns and operates the award-winning facility at the Mankato Wastewater Treatment Plant. Calpine paid for design and construction of the facility, and the MPCA expedited the city’s National Pollutant Discharge Elimination System (NPDES) permit renewal and plan approval in implementing the reclamation and reuse project.
Treating effluent from the Mankato Wastewater Treatment Plant (WWTP) to meet specific water reuse criteria and conveying it by pipeline to the new, Calpine-owned Mankato Energy Center for use in cooling at the natural gas-fired turbine simultaneously reduces demands on the local surface and groundwater supplies and improves the quality of the reused water eventually returned to the river, according to retiring Mankato Public Works Director George Rosati.
“This is a great example of an innovative and sustainable infrastructure solution that is successful on many fronts,” said Rosati, who spearheaded the project for the city. “The project yielded multiple economic and environmental benefits for the partners and the people of Mankato, and earning the award was yet another win. Black & Veatch’s creative ideas, technology leadership and teamwork were important factors in this outstanding project.”
The WRF is a dual-purpose facility designed to provide two stages of tertiary treatment for the city’s treated effluent. The first stage provides phosphorus removal for all of the WWTP’s current and future needs. The second stage of the tertiary treatment system provides additional filtration and chlorination to meet reuse requirements established by MPCA based on California’s Title 22 Health Laws for recycled water.
The Mankato Energy Center produces electricity as demand dictates, operating approximately 60% of the time. At this operating rate, an estimated 679 million gallons of water will be saved each year through reuse.
The cost for the WRF was nearly $20 million. The city, which otherwise would have needed to build the stage-one facilities to comply with new phosphorus limits within a few years, saved approximately $10 million. Savings to Calpine include the operational and maintenance costs of the WRF, which are anticipated to be approximately $500,000 per year over the 20-year agreement. Potable water cost savings for Calpine will exceed $1.5 million annually.
The 11.25 million gpd WWTP serves Mankato and five other cities/districts. New Minnesota water quality requirements limit cities along the Minnesota River, including Mankato, to a stringent (1 mg/l) total phosphorus limit by 2015 to prevent algal blooms and subsequent pollution problems. Since the WRF began operation in April 2006, biochemical oxygen demand has dropped from 1.6 mg/l to undetectable levels, and total phosphorus levels have dropped to 0.35 mg/l.
Source: Black & Veatch
