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Waste Makeover

Food processors in this central Minnesota town don’t want to eliminate their waste. They want to digest it.

Perham hopes to pool food-processing waste and send it to an anaerobic methane digester where it would be converted to renewable biofuel. AURI and Minnesota corn and soybean grower groups are helping evaluate the idea’s technical and economic feasibility.

Digesting organic waste could relieve Perham’s overburdened municipal wastewater treatment system, says Chuck Johnson, Perham economic development director. A community digester could also cut industries’ waste disposal costs and provide a new revenue source.

Anaerobic digestion is a microbial process that produces methane and carbon dioxide, or “biogas,” from organic materials. A natural-gas substitute, biogas can be burned in a furnace or purified to power a generator.

Anaerobic digestion has long been used in food processing and waste treatment plants, says Jill Mickelson, an engineer with St. Paul-based Short, Elliot, Hendrickson, which is doing the Perham feasibility study. But those digestion systems are designed mainly for wastewater cleanup rather than fuel production, she says.

Now there is growing interest in the renewable energy potential of anaerobic digestion, she says. Dairy farms, for example, have started digesting manure to generate electricity. Ethanol plants are looking at digesting distillery byproducts to power their dryers. Even sewage is getting a makeover. “Instead of thinking of it as waste,” Mickelson says, “think of it as fuel.”

Food processing town

Methane generation could be a very nice fit for Perham, says Michael Sparby, AURI project director.

The community of 2,800 boasts half a dozen food manufacturers including snack-maker Barrel O’ Fun, Kenny’s Candies, Nelson Confections and Tuffy’s Pet Foods. Primera Foods operates an egg products plant. Potato producer R. D. Offutt has a large warehouse at Perham, and Bongards Creameries, a 413-member dairy cooperative, processes 700 million pounds of milk at its Perham cheese and whey plant.

These industries generate lots of organic waste, which is expensive to dispose of and puts a heavy load on Perham’s sewage treatment system, now operating at nearly 100-percent capacity. As a result, some companies have built their own wastewater treatment systems or trucked food scraps to farms for livestock feed or fertilizer.

Barrel O’ Fun is one of Perham’s leading “homegrown” companies. The manufacturer makes salty snacks, including potato chips, corn and tortilla chips and gourmet popcorn. The plant generates about 36,000 gallons per day of corn and potato waste. The material is pre-treated to remove the water, which goes into the city sewer system. The remaining solids are sold as cattle feed. “We’ve looked at how to better use our waste stream,” says CFO Wayne Caughey. Methane digestion “is something that merits further study.”

Anaerobic digestion could have several advantages for the rapidly growing company, which added 100 workers last year and now employs 550, Caughey says. “It would be a local use. And we might be able to use the methane as a replacement for natural gas.”

Perham would benefit, too, he adds. “Anything we can do to reduce the amount of water going into the municipal system would be an advantage.”

Perham-area dairy and poultry farms are also interested in supplying manure and other organic waste to a community digester, Johnson says. “We’re excited about this,” says Doug Huebsch, owner of NewLife Farms and an Otter Tail County commissioner. NewLife produces 8 million hatching eggs a year for the Jennie-O Turkey Store.

The farm sends most of its turkey manure to Fibrominn, a 55-megawatt biomass electricity plant in

Benson. NewLife Farms also generates a ton a day of egg parts and dead turkeys. Many poultry producers send their mortalities to a rendering plant, Huebsch says, “but we don’t have a plant nearby.”

Instead, he composts the waste and spreads it oncropland, but “it’s a really labor-intensive job,” he says. He estimates that his turkey mortalities could be worth up to $200 a day as methane, “and it would be a better way to deal with our waste.”

Bench-scale tests last year looked at how much biogas might be generated from Perham’s organic waste. Rough estimates suggest that a community digester could produce 360,000 cubic feet of methane per day, worth more than a half-million dollars annually, Sparby says.

More biogas markets

In addition to abundant supplies of organic waste, Perham has several potential markets for biogas, Johnson says. The gas could be burned in the city’s garbage incinerator, which sells steam to Bongards and Tuffy’s Pet Foods. Methane would replace natural gas, which supplies about 30 percent of the incinerator’s British thermal units, Johnson says.

Another potential outlet is Perham’s municipal-gas utility. “We could clean up the biogas and inject it into the natural-gas pipeline,” Johnson says.
Methane could also generate renewable, baseload electricity for sale to the power grid. Or the biogas could go back to local food-processing plants to cut their natural gas consumption.

The solids remaining after anaerobic digestion “make a nice fertilizer,” Mickelson says. The nutrients “are passed through basically intact,” while the high heat of digestion destroys most pathogens and odors.

A technical challenge

Phase two of the feasibility study, now underway, will look at nuts-and-bolts questions, such as digester design and permitting, location, feedstock handling and storage, biogas markets, capital costs and economics. Preliminary estimates put the cost of a community digester at $2 to $4 million, Sparby says.

One big technical challenge, Mickelson says, is digesting a mixed waste stream of such diverse materials as liquid manure, corn-chip crumbs and turkey, chicken and beef parts. Still, she adds, methane-digestion engineering has advanced rapidly in the last five years, especially in Europe.

“There’s lots of enthusiasm for the project,” Johnson says. Although a similar effort fizzled in Perham several years ago, Sparby says this time, “there’s an unusual willingness to come together and collaborate.”

Says Huebsch, “We’re looking to be part of the renewable-energy revolution.”