New technology at POET Biorefining – Bingham Lake, Minn. has eliminated wastewater discharge, a development with far-reaching effects on the environment and community resources.
The move to what is known as ‘zero liquid discharge’ (ZLD) –implemented the first week in January — is the first among Sioux Falls-based POET ethanol plants. It won’t be the last.
Two years ago, POET officials began work on improving the quality of water that leaves the plant. Once it was determined that discharged water could reach a high-quality level, Don Brock, Regional Vice President of Operations for POET, recalls the conversation shifting from discharging the water to reusing the water instead.
CHANGING THE STANDARD
The Bingham Lake plant is slashing water usage per gallon of ethanol produced from 3.4 gallons to an estimated 2.6, a 23 percent decrease that places POET well below the industry average.
In POET’s patent pending ZLD process, the plant will continually filter or treat recycled water to remove certain things and manage water qualities for use elsewhere in the plant. The only water leaving the plant will be in the form of vapor or in the leftover mash known as dried distillers grains with solubles — a valuable cattle feed.
“Zero liquid discharge is a technological breakthrough for POET. We’re either recycling all the water or it winds up becoming water vapor,” said Randy Dittmann, General Manager at POET Biorefining in Bingham Lake. “This is a very big step forward, demonstrating our proactive approach toward protecting the environment.”
The move to ZLD continues to accentuate the environmental benefits of ethanol production. The water previously discharged at Bingham Lake met the requirements of all industrial discharges into the environment regulated by the Minnesota Pollution Control Agency and the Minnesota Department of Natural Resources.
The move makes sense both environmentally and economically, says Nate Mosier, an agricultural engineer at Purdue University who studies the operation of ethanol plants. From a community standpoint, Mosier understands the initial concern small communities have about the environmental impacts of an ethanol plant.
“Being able to say that they have no water discharge is a good thing,” he said.
“There is a drive for POET to continually reduce any impact on the environment and help us reduce our costs as well,” Brock said.
The changes to the plant are relatively minor and can be accomplished company-wide at a reasonable cost. Brock estimates the changes will pay for themselves at a given plant within two years.
Retrofitting the plant began last summer and continued into the fall. Bingham Lake is the second oldest POET ethanol plant (1997), which bodes well for making the change within the rest of the group.
COMMUNITY GAIN
Not only has the move to zero liquid discharge helped POET cut costs, it is providing the town of Windom, in farm-rich south-central Minnesota, with an addition to their water supply.
The tiny community of Bingham Lake, as well as POET, purchases water from the Windom municipal system, says Steven Nasby, Windom’s City Administrator. POET, which operates the plant in partnership with Southwest Minnesota Agrifuels Co-op, used about 36 percent of Windom’s capacity.
ZLD will reduce what the company will have to buy by about 20 million gallons each year — more water the city now has at their disposal.
“It’s a huge benefit to the city,” says Nasby. “That’s another 20 million gallons in our back pocket for when there is a drought, but also for business and residential expansion.”
Windom can’t legally pump more than 420 million gallons per year, Nasby said. The past several years the city has used between 375 and 400 million gallons annually from their aquifer-fed wells.
INDUSTRY BENEFITS
The move is definitely a good one for the industry, says Dennis Keeney, a professor emeritus at Iowa State University and a former director of their Leopold Center for Sustainable Agriculture. “When you watch water leaving the plant as a discharge, it’s logical to think you would much rather re-use that water [than buy new].”
Keeney was a coauthor, in 2006, of the report: Water Use by Ethanol Plants, Potential Challenges, published by Institute for Agriculture and Trade Policy based in Minneapolis, Minn. At that time, water use by ethanol plants in Minnesota ranged from 3.5 to 6 gallons per gallon of ethanol produced. He says a plant might be able to reduce water usage to nearly 2 gallons for every gallon of ethanol produced, roughly the same amount of water used to produce a gallon of gasoline.
“I don’t know what that next barrier is,” says Brock. “But we’ll be looking at those processes to maximize even more. As for more water reduction, yes, I think it’s possible.”
