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Will Energy From Manure Help or Harm Water Quality in Michigan?
Michigan Ag Connection - 12/08/2023

Gov. Gretchen Whitmer’s plan to generate all of Michigan’s energy from renewable sources by 2040 is meant to limit climate change gases. It also has consequences for improving or damaging the state’s waters.

Replacing polluting fossil fuel plants with cleaner energy sources would limit oil pipeline spills, curtail mercury contamination, and halt discharges from coal-fired power plants. But those benefits could be easily overwhelmed by the development of a new renewable energy sector to produce methane from one of the state’s largest causes of water contamination –liquid manure produced by large livestock feeding operations.

The conversion from animal wastes to methane occurs in industrial-scale manure biodigesters. The Red Arrow Dairy in Van Buren County, where two biodigesters rise like giant white mushrooms from fallow fields, displays an apt example of the new energy-generating equipment. Liquid manure, 200,000 gallons daily from nearly 6,000 cows, pours into the digesters, which slowly cook the urine and feces in a warm oxygen-deprived (anaerobic) broth. The result is a stream of methane that is collected and processed for vehicle fuel.

Prompted by changes in state regulations, and federal and state taxpayer incentives worth hundreds of millions of dollars, Michigan in the last two years has been the largest center of manure biodigester development outside California, according to state and federal figures. At a cost of $15 million to $20 million apiece, according to industry data, the new energy sector is attracting big players in Michigan.

The Red Arrow Dairy digesters and four others have been constructed on dairies in west and southeast Michigan by Brightmark, a joint venture of Chevron. The California oil giant promotes its investment as “finding inspiration in nature.” Four more biodigesters have opened near the Lake Huron shoreline by South Jersey Industries, a New Jersey natural gas supplier. Altogether the 10 new digesters in operation handle roughly a million tons of manure from 45,000 cows, 10 percent of the state’s dairy herd.

Consumers Energy has a digester under development at Swisslane Farms in Kent County. The farms gain new revenue from contracts to sell manure to Consumers, which was awarded a $5 million state development grant, and owns and operates the equipment. “There is a lot of good that can come out of it,” said Anna Link, one of the Swisslane principals. “It fits in with the core values of our farm and sustainability goals.”

Among the most credible advocates for farm-based biodigestion is Michigan State University’s Anaerobic Digestion Research and Education Center. “Done right, digesters work well,” said Wei Liao, an MSU professor and the center’s director. Liao oversees a decade-old biodigester and a state-of-the art demonstration program that converts 14,000 gallons daily of food waste and manure from 250 cows. Methane from the digester fuels a generator that feeds electricity into the university’s grid. Digestate solids are sold as compost. Nutrient-rich liquids are spread as fertilizer on campus farm fields. Water quality is monitored across the campus. And Liao’s center is developing technology to strip nitrogen and phosphorus from digestate for sale as commercial fertilizer.

But Liao also acknowledges that digestate can be ticklish. “If you don’t manage digestate land application, there are some consequences, negative consequences,” said Liao.

And that’s the principal cause of concern for critics. Digestate has different chemical properties than raw manure. The cooking process concentrates nitrogen and phosphorus, making both elements more readily available for plants and more mobile in the environment. The second concern is that disposing the millions of gallons of digestate is regulated by the state Department of Environment, Great Lakes and Energy under rules for livestock manure that are a decade old and plainly inadequate, say critics.

Big livestock operations can spread manure and digestate on cropland already saturated with phosphorus. They can apply manure and digestate on the slippery hard ground of winter, something that Ohio outlawed in 2015. Neither the state nor the federal government can issue penalties if a storm causes storage lagoons to overflow or manure to run off crop land.


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