How can yogurt make electricity?
The boom in Greek yogurt has also led to a dramatic increase in waste. But our facility in Murfreesboro, Tennessee, may be the only Greek yogurt plant anywhere to produce electricity from that waste.
Since August of 2015, the plant has been processing its leftover whey from Yoplait Greek lines and using it to produce 10 percent (1.6 megawatts) of the plant’s electrical needs.
In addition, excess heat from its biogas generator has reduced the plant’s natural gas needs by an additional 10 percent.
“This is a win-win for everyone involved – from the community to General Mills,” says David Tincher, plant manager. “Not only are we reducing our greenhouse gas footprint by about 9,000 metric tons per year, but we’re also saving roughly $2.4 million annually.”
How does it work?
Greek yogurt is made from milk which has had its cream and whey separated to achieve the right protein and density. While it takes a gallon of milk to make a gallon of traditional yogurt, it takes three gallons of milk to make one gallon of Greek yogurt.
That creates the problem of significant leftover Greek whey. And the Greek whey contains too many organic solids to send directly to the municipal wastewater treatment plant.
In the past, this waste was trucked and spread onto a farm field – more than 15 tanker truckloads a day.
In 2014, the plant constructed a six million gallon covered holding tank, known as an anaerobic digester, at the plant’s waste water pre-treatment facility. The Greek whey is now sent down the floor drains to combine with the rest of the plant’s process wastewater.
The whey serves as a food for the self-renewing bacteria in the digester. The bacteria breaks down the whey, purifies BOD (biochemical oxygen demand) from the water, and generates methane biogas as its byproduct.
“This sustainable energy project could be a model for other entities to follow in the future,” said Mimi Keisling, environmental education coordinator for Rutherford County, Tennessee, in the Murfreesboro Daily News-Journal.
In 2015, another system was installed to collect the methane and use it to fuel a biogas engine that generates electricity.
“The system has been online since August and has been working very well,” said Daren Kaiser, the plant’s technical manager. “We’re not aware of any other Greek yogurt plants that are using whey to make electricity on-site.”
But we have been putting leftover whey to good use at other locations. At our Yoplait Liberte’ yogurt facility in Saint-Hyacinthe in Quebec, Canada, leftover whey is being used to produce natural gas.
And since 2008, our Häagen-Dazs ice cream facility in Arras, France, has been generating electricity from its wastewater.
Since 2010, our oat-milling facility in Fridley, Minnesota – which supplies the oat flour to make Cheerios and other products – has been burning leftover oat hulls to generate electricity.
The efforts at the plant are part of our ongoing efforts to trim our energy use and our greenhouse gas emissions. In August of 2015, General Mills pledged to reduce its absolute greenhouse gas emissions by 28 percent across our full value chain – from farm to fork to landfill – over the next 10 years from our 2010 baseline.
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