On large dairy farms with lots of cattle, manure management is no minor task. Farmers have to be deliberate about how they store it, and mindful of the environmental impact of mountains of manure.
And then there's the odor. Some of the traditional ways that farmers have stored manure — in holding pits called lagoons, for example — are understandably unpopular with neighbors.
Odor control is one reason that Noblehurst Farms — a dairy farm in York, Livingston County — installed an anaerobic digester in 2001, says Chris Noble, the farm's vice president. The system functions like a big stomach, and uses an oxygen-deprived environment to break down manure and other organic matter into a considerably less pungent material called digestate.
But the digester has another big benefit: it produces a combustible mix of methane and carbon dioxide that the farm uses to fuel a combined heat-and-power system. Noblehurst upgraded its digester last year, and the farm is now able to generate more electricity than it can use, Noble says.
The system is connected to the power grid, and the local utility, National Grid, credits the farm for excess electricity.
The farm should fully recoup its $3.5 million investment, Noble says, which was partially offset by state and federal grants.
"We can reduce the cost of producing milk by essentially producing our own electricity with our own manure," he says.
Anaerobic digestion is an old technology for breaking down and managing organic waste, and has traditionally been the domain of large farms like Noblehurst and municipal waste water treatment plants. But the idea that the digesters can also be a source of renewable energy is newer, and it's starting to catch on beyond the farm.
In 2012, the F.X. Matt Brewery in Utica, which is probably best known for its Saranac beer, built an anaerobic digester system at its facilities. The system breaks down brewing residue and uses the resulting biogas to generate electricity for the brewery.
And Genesee Biogas has proposed an anaerobic digester and generator system for the Genesee Valley Agri-Business Park in Batavia. The system would run on yogurt production waste water from the Alpina and Müller Quaker Dairy yogurt plants — both companies currently pay to have the waste treated off-site.
But farms have also identified larger opportunities for the digester systems. Some of them, including Noblehurst, have started taking in organic waste from nearby food processors and grocery stores, as well as other farms. They've found that food scraps in particular can boost the production of biogas in the digesters, which means more low-cost energy for the farms.
Government agencies, including the US Department of Agriculture and the New York State Energy and Research Development Authority, encourage the use of digesters and offer financial incentives to support them. Some environmental groups also view them favorably and place anaerobic digesters right alongside composting as a preferred way to deal with inedible food wastes.
Other environmentalists are skeptical, however, and question whether large-scale community composting projects might do more to reduce emissions from food waste, and at a lower cost.
Each year, America collectively tosses approximately 40 million tons of food waste into the trash. Much of that organic matter ends up in landfills, where it decomposes and generates methane.
Methane pollution is a serious issue because of the gas's contribution to human-influenced climate change. And domestically, landfills are the third-largest source of methane emissions, ranking behind the gas and oil industry and farm animals.[image1-1]
Enter Wegmans. The company has a hierarchy for edible food, which stresses selling it, using it in prepared foods, or donating it. It's the inedible food scraps from its growing prepared-food operations — rinds, stalks, and other trimmings — that have posed the greatest challenge.
But for the last 18 months, 11 stores in the Rochester region and one Buffalo store have been piloting a program to divert inedible food scraps from landfills. Employees fill up designated bins with inedible food waste and wheel them outside of the store. The contents are picked up several times a week and taken to digesters at either Noblehurst or Lawnhurst Farms in Stanley, east of Canandaigua.
"On the lower side, it's two-and-a-half to three tons a week — that'd be a smaller- volume store," says Jason Wadsworth, Wegmans' sustainability manager. "The largest volume store is upward of seven tons a week."
By the end of next year, Wegmans expects to add another 20 stores in the Rochester, Buffalo, and Syracuse areas to the diversion program, Wadsworth says. The stores will send their scraps to either digesters or composting facilities, he says.
Wegmans pays a company, Natural Upcycling, to haul away the food waste (Noblehurst is a partner in the hauling company), and it pays Noblehurst and Lawnhurst to digest the waste. But it doesn't cost the grocer any more than it would to send the discards to a landfill, Wadsworth says.
"It's really a philosophical issue," he says. "We don't believe in sending things that have a second benefit to a landfill."
And given the growing potential to turn food waste into energy and other useful byproducts, the financial dynamic will probably shift, Wadsworth says. He likens it to cardboard: companies used to pay recyclers to take the stuff, but as the market for recycled cardboard grew, the recyclers started taking it for free. Now, recyclers buy cardboard.
When Noblehurst upgraded its digester, farm officials intentionally built in capacity for outside food waste.
"We felt there's a growing need on behalf of supermarkets and food manufacturers to find alternative ways to dispose of their food waste, rather than burying it into a landfill," Noble says.
Noblehurst's digester takes in approximately 40,000 gallons of cow manure each day, which makes up about half of the system's input. The farm's permits allow it to take in food waste for the other half. In addition to the Wegmans scraps, the farm brings in waste water from a neighboring milk-processing plant and some other nearby processors, Noble says.
It's important to note that digesters don't entirely eliminate carbon emissions from farm and food waste — but neither does composting. They can, however, be effective at reducing those emissions, especially when there are large amounts of organic material, says Tom Trabold, an associate professor at RIT's Golisano Institute for Sustainability. Trabold has assisted with emissions analyses of farm-based digesters and advises a graduate student who has studied the issue.
The how and why of those emissions reductions become complicated quickly. The benefits come from capturing the biogas, which is three-quarters methane, and converting it into electricity and heat, Trabold says.
That energy can displace electricity and heat from fossil fuel natural gas, Trabold says. The newer systems also operate as closed loops, and recirculate heat and emissions from the generator back into the digester, which uses them in its process.
Some digesters have had problems with nitrous oxides and other nitrogen gases, but the systems are better now at minimizing and capturing those emissions, says Darby Hoover, a senior resource specialist for the Natural Resources Defense Council. Nitrogen gases can contribute to elevated ground-level ozone in urban areas and they have a greenhouse effect in the atmosphere.
The idea of producing energy from cow poop and food scraps is attention-grabbing. But the process also creates another product: a nutrient-rich goop known as digestate. Hoover says that the material improves soil health.
The digestate allows farmers to return nutrients to the soil, and when combined with bulky compost, it can be especially restorative, she says. It also gives farmers the opportunity to replace synthetic fertilizers, which are often petroleum-derived, with fertilizers made from organic materials, she says.
The nutrient-rich liquid is also easier to store and transport than manure, she says. And farmers can better control how they apply it to their fields, which means a reduction in the amount of nutrients — including problematic phosphorous and nitrogen — running off into waterways during heavy rains.
Noblehurst uses the liquid from its digester as fertilizer for its 2,600 acres of its corn, hay, wheat, and straw crops, Noble says. It also plans to use the solid, bulky part of the digestate for cow bedding, which would save the farm $150,000 a year, he says.
It's encouraging, Hoover says, that farmers and food companies have found a viable way to keep organic wastes out of landfills. That they're using the digesters' byproducts to restore soil, and are looking beyond the energy benefits, is also positive, she says.
"Waste inherently represents some kind of inefficiency, so if you can eliminate waste by redefining it as a value-added product, then absolutely you achieve something that's economically and ecologically preferable," Hoover says.