The Twin Cities’ Metro Council looks everywhere for opportunities to save energy and deploy renewable energy sources.
In 2007, the Environmental Services Division of the Metropolitan Council in Minneapolis/St. Paul set a goal to reduce its fossil fuel purchases by 15 percent by 2010. After achieving that goal, the division aimed for a 25 percent reduction from the 2006 baseline by 2015.
The division came up just short, according to Sara Smith, sustainability in operations manager: “We came to a reduction of 23.6 percent, so we didn’t meet the goal, but we were very close. It was a good goal.”
It was close enough that the division has challenged itself with a new goal of a 10 percent reduction from 2015 levels by 2020. “The idea is that we’ll keep that goal rolling and reduce our purchases by at least 10 percent every five years,” Smith says.
The Metropolitan Council is a regional body serving the seven counties and 181 cities and towns in the Twin Cities area. The Environmental Services Division operates and maintains 600 miles of regional sewers and eight wastewater treatment plants that process on average 250 mgd. The council also coordinates mass transit, community development planning, water supply planning, lake and river monitoring, regional parks and trails, land use planning and affordable housing.
A cross-functional Energy Team meets quarterly to work on projects across Environmental Services. “We initiated the team in 2007 to bring together maintenance, operations, people looking at process efficiency, and technical services where capital projects are designed and implemented,” Smith says.
Aeration accounts for 30 to 60 percent of the treatment plants’ energy costs. “We’ve done a lot with optimizing our aeration systems and saved about 30 million kWh per year,” Smith says. “One of the biggest efficiencies was switching from coarse-bubble to fine-bubble diffusers. All the efficiency work was on the diffuser and setpoint side of the aeration process.
We did look at our blowers a few years ago and determined that they were efficient and a good match for our system.”
The division also switched to more efficient motors throughout the collections and treatment systems and added variable-frequency drives, saving 1.2 million kWh a year.
The Metropolitan plant, the agency’s largest wastewater facility, has two large fluidized-bed biosolids incinerators that create steam for heating and to produce about 20 percent of the plant’s electrical needs from 240 dry tons of solids per day. “In 2015, our steam turbine averaged more than 2 MW of generation that resulted in $1.2 million in savings for ratepayers,” Smith says.
Normally, the turbine generator had been used more in summer, but low natural gas prices changed that strategy. “There are times when we’ve decided that it was better to run the turbines for electricity and purchase natural gas for heating,” Smith says. “It’s not necessarily displacing energy usage, but it’s a financial savings.”
The division has also made several lighting upgrades, the largest being the replacement of old fluorescent, high-intensity discharge and incandescent lights with T8 and T5 fluorescents in 5 miles of tunnels at the Metropolitan plant. That was before LED lights became cost-effective, but it still saved significant energy. “Systemwide, we’ve seen about 3 million kWh of annual savings,” says Smith. LED lighting is planned for the next tunnel relighting project at the Seneca plant.
Buildings have also received updates to HVAC and other systems. “We save about 7 million kWh a year with all the work that we’ve done,” says Smith.
Those efforts are aided by Xcel Energy, the local electric utility, which has funded studies that identify conservation and rebate opportunities, especially in lighting and building systems. “Xcel pays about $25,000 to $30,000 for each study, and a number of energy projects are identified,” says Smith. “It helps them meet their energy conservation goals as we use less energy, and we’re one of their top users.”
Part of the process
Energy and emissions reductions have become a normal part of planning and designing all capital projects. “We look at as-is conditions — what if we just kept fixing what we have to make it work, versus the alternatives,” Smith says. “When we look at energy costs, it can tilt the scale from one alternative over another. We look at it from a financial standpoint, but also from an environmental standpoint.”
For projects driven by energy use, lifetime cost is a key driver: “If the project has net present value savings greater than zero over the life of the project, and we have funds available, we will implement the project.”
Renewable energy is part of the agenda. “We’ve looked at a number of options for installing solar on our property and participating in solar programs,” says Smith. A 5,000-panel, 1.57 MW photovoltaic system at the Blue Lake Wastewater Treatment Plant went into operation early this year, providing 10 percent of the plant’s energy. It is operated by Oak Leaf Energy Partners, which helped develop the project. All the power is sold to the plant through a power purchase agreement.
The agency also takes part in Xcel’s Solar Rewards Community program, buying a share of the electricity from solar gardens in exchange for monthly bill credits. Three solar garden installations totaling 3 MW were under construction in 2016 at the Blue Lake plant; five will be built at the Empire plant and one at the Seneca plant on a closed ash landfill.
Environmental Services and Metro Transit, also operated by the council, will each subscribe to 40 percent of the production, and the remaining capacity will be available to municipalities served by the council.
Also in the planning stage is a combined heat and power engine at the Empire plant. Biogas at Blue Lake replaces about 9 million Btu per hour of fossil fuels.
The Environmental Services Division spends about $17 million a year on energy, and the transit facilities spend another $3.6 million, excluding fuel. By focusing on sustainability, both significantly reduced the fossil energy they buy, saving money and helping the environment.
Large and small
The Metropolitan Council owns and operates eight wastewater treatment plants. These facilities and their design capacities are:
- Blue Lake – 32 mgd • Hastings – 2.34 mgd
- Eagles Point – 10 mgd • Metropolitan – 251 mgd
- East Bethel – 1.22 mgd • Seneca – 34 mgd
- Empire – 24 mgd • St. Croix Valley – 4.5 mgd