Treating 250 million gallons of wastewater a day ensures clean water and public health, but it also uses a lot of energy.
With a goal of efficient operations and protecting the environment, Metropolitan Council Environmental Services (MCES) is laser-focused on reducing reliance on fossil fuels and promoting alternative energy.
It’s no small challenge. MCES, which serves the seven-county metro area, is among the biggest energy users in the state.
“We used to be in the top three of Xcel Energy customers,” said Sara Smith, MCES Sustainability Manager for Internal Operations. “Now we’re in the top 10, so we’re working our way down in usage and that’s a good thing.”
How are they doing it?
Smith says it’s the result of teamwork—bringing together staff from maintenance, operations, technical services, as well as those who examine processes and ways to create efficiencies.
Harnessing the sun to fuel Council operations
Solar energy is MCES’s most recent foray into the energy arena—installing solar arrays on Council property and participating in various solar programs.
A new 5,000-panel solar photovoltaic system at the Blue Lake Wastewater Treatment Plant in Shakopee provides the equivalent of 10% of the plant’s annual energy needs. Oak Leaf Energy Partners operates the solar facility, developed with SunEdison. All the power is sold to the plant through a power purchase agreement.
MCES participates in Xcel’s Solar* Rewards Community Program and subscribes to a share of the electricity from solar projects--in exchange for credits on its monthly bill. Three solar garden installations, totaling three megawatts, will be built this year at the Blue Lake plant. (The annual energy a 3MW system can produce is equivalent to the energy used by 500 homes.)
Also this year, five solar gardens will be built at the Empire Wastewater Treatment Plant near Farmington. One will be built at the Seneca Plant in Eagan. MCES and Metro Transit, also operated by the Council, will each subscribe to 40% of the energy production, while the remaining capacity will be made available to municipalities served by the Council.
But not all efficiencies are found in new technologies. Some are attributed to improving the efficiency of existing infrastructure.
Optimizing the wastewater treatment process
Smith says MCES staff targeted the wastewater aeration process, because it’s a large energy user in any treatment system. During this process, oxygen is infused into the effluent, creating a haven for the bacteria that eat the pollution.
“We’ve done a lot to create efficiencies in the aeration system, for a savings that’s equivalent to about $2 million a year, or the electrical use of 3,000 households,” Smith said.
She also credits two large biosolid fluidized bed incinerators for energy savings at the big Metro Plant in Saint Paul. Waste heat boilers on the incinerators produce steam that heats all the buildings on the 170-acre Metro Plant campus.
“In 2015, our steam turbine averaged more than two megawatts of generation that resulted in a $1.2 million savings for ratepayers,” said Smith.
The slate of projects that help to reduce fossil fuel consumption also includes replacing the lighting in the Metro Plant tunnels and updates to HVAC and other building systems.
A combined heat and power engine at the Empire Plant is in the planning stages. And, methane biogas recovered from the anaerobic digester at the Blue Lake plant is used to replace about nine million BTU/hour of fossil fuels, equivalent to heating 1,350 homes a year.
Setting new goals for the operations
MCES, and the Council overall, is always looking for ways to create efficiencies in its operations.
In 2007, MCES set a goal to reduce fossil fuel purchases 15% by 2010. After achieving the goal, MCES upped the ante and set a new goal to 2015—a 25% reduction from the 2006 baseline.
MCES came so close, achieving a reduction of 23.6% by the end of 2015, before setting a new goal of a 10% reduction by 2020.
‘We expect that to be a rolling goal—reducing energy purchases 10 percent every five years,” said Smith.
“It’s an exciting time to be involved in sustainability initiatives,” said Smith. “The Council spends about $17 million a year on energy. By focusing efforts on reducing our dependence on fossil fuels and promoting alternative energies we not only save money, but we help the environment. That’s what this industry is really all about.”