The anaerobic digester that Steve Reinford installed on his Pennsylvania dairy farm three years ago cost a million dollars, but he can already count the ways it pays for itself.
Energy from the digester, which turns cow manure into methane, powers about 100 homes in the Central Pennsylvania valley where Reinford raises his 500 dairy cows. While the rest of us pay the power company, Reinford doesn't; they send him a check every year.
He's able to use his digester and its many byproducts to heat his home and milk house, make bedding for his cows, fertilize his fields, dry his corn and pasteurize the milk he feeds his calves - saving him money and making him feel like the environmental steward he had always hoped to be.
"Six years ago, people said, 'there's no way you're going to get electricity out of cow manure,'" Reinford said. "But we're doing it, and we're doing very well."
The digester technology is fairly straightforward: Billions of tiny bacteria consume the waste and turn it into methane, which then can be a source of power. In addition to the gas, the process leaves a farmer with liquid manure for his fields and a solid that can be used for cow bedding and landscaping. And digesters are hardly new; Pennsylvania alone has two dozen of them, the first of which was installed more than 30 years ago in response to the Arab oil embargo.
But now the humble digester - and similar technologies that extract energy from waste - are shaping up to be the star in what could be called the Manure-to-Energy Moment.
The moment is born out of a collision of priorities: the need to reduce the United States' dependence on foreign oil, the need to clean up the Chesapeake and in particular, the drive to find non-polluting ways to handle the region's massive amounts of animal waste. Manure accounts for about 15 percent of the nitrogen and 36 percent of the phosphorus that reaches the Chesapeake. The EPA's new pollution diet requires the six states and the District of Columbia to remove 60 million pounds of nitrogen and 4 million pounds of phosphorus by 2025. To meet that goal, the states have got to tackle their manure problem, and manure-to-energy technology offers hope.
Can it do for the watershed what it has done for Reinford?
While the technology has many pluses, it remains unclear whether it can be a significant player in the drive to reduce water pollution caused by runoff from fields fertilized with manure. The manure is digested and energy-rich gas is created. But nitrogen and phosphorus, the two polluting elements, remain in new, but still potent, forms.
"I've been around too long and I've heard too many grand statements. Biogas is not going to save the Bay," said Robert Graves, a professor in the Department of Agriculture and Biological Engineering at Penn State University. "Coming out of the digester, there are no less nutrients than there are coming in. If everyone would just understand that."
Nonetheless, the technologies have benefits.
Stephanie Lansing, a professor of agricultural engineering at University of Maryland who has focused her research on digesters, argues that looking at digesters as "nutrients in, nutrients out" only tells part of the story. The digester, she argues, does let a farmer apply less nitrogen and phosphorus to his fields by giving him more options.
Farmers, she said, can put the digested manure through a treatment wetland as a disposal solution, or do drip irrigation with it for a more precise application that results in less runoff. One farmer is using his solids to make "cowpots" - landscape pots that he sells to gardeners. Many farmers use the solid fibers as bedding. What they don't use, they sell to other farmers, getting the nutrients "off the farm."
Also, Lansing said, plants fed the liquid left after the digestion process can take up more of the nutrients than they can from straight manure, because its chemical composition makes it easier to absorb. That means farmers, including Reinford, do not have to buy commercial fertilizer, nor do they have to plow in the digested manure to control odors, because the digester removes the ammonia and therefore, the odor. Farmers can immediately follow a manure application with no-till seed planting. And, not plowing up the soil means less erosion and less nutrients arriving in waterways.
"I think it's a narrow approach to just look at water quality," Lansing said of the debate about digesters. "It's not a silver bullet, but if you look at all the benefits, I think it's a thing you really need to implement."
One of the biggest benefits is powering the planet. The Central Vermont Public Service Corp. began its "cow power" program to turn manure into energy seven years ago. It has 10 farms providing power to 3,300 households and 200 businesses. Eight more will come online in the next three or four months.
Residents pay about $7.50 a month extra for the "cow power," said David Dunn, the utility's manager of renewable projects. Like Pennsylvania, Vermont's dairy farms are mostly small, with the state's largest housing just 1,500 cows.
Pennsylvania requires power companies to purchase 18 percent of their energy from renewable sources by 2020; Maryland requires 20 percent by 2022, and is considering requiring power distribution companies to purchase a small amount from manure-to-energy sources, much like some states already do for solar. Vermont does not yet have a mandatory renewable energy standard. Nor has it aggressively marketed the program. But in a small state with a strong environmental protection ethos, Dunn's Rutland-based utility has about 3 percent of its customers on cow power.
Chesapeake Bay Commission Executive Director Ann Swanson, who has talked extensively with Vermont officials about their manure-to-energy efforts, said she is becoming a believer in the technology's potential. She says it gives the farmer more options to turn manure into beneficial products and move it off the farm.
"The longer we look at it, the more it is going to make sense," she said. "When you look at the different types of energy, some of them, like wind, are non-
polluting. However, none of them, other than this one, reduces pollution. And that is pretty amazing."
The commission recently released a report, "Manure to Energy: Sustainable Solutions for the Chesapeake Bay," after a summit in Baltimore with farmers, entrepreneurs and policy makers to discuss the technologies' benefits and limitations.
Swanson said the report has been one of the commission's most popular - second only to one done a few years ago on the best bang-for-the-buck solutions to cleaning up the Bay.
The report notes that with advanced processes, the slurry left after manure is digested can be separated into forms that have a higher value than raw manure and are more readily transported. But the report said it is still not economical to transport the liquid manure or solids far. Many areas where animal production is the heaviest can't readily accept more manure because the soils are already saturated with phosphorus, so new applications must be found for the byproducts.
The report suggested that if phosphorus can be separated from the wastes, a market may emerge in regions that need this nutrient.
Digestion, the best developed of the processes, is suitable for cow and swine manures, which have a high moisture content, but digestion does not work well on poultry manure, which is drier. Other technologies - such as gasification, combustion and pyrolysis - need to be further developed to effectively convert poultry wastes to usable byproducts and energy.
The National Fish and Wildlife Foundation recently announced a Farm Manure to Energy Initiative that will make nearly $3 million available to examine how to remove phosphorus in the process. If the project succeeds, it could create a product that can be transported to areas in the country that have a phosphorus shortage.
In the case of digesters, the technology is as old as time. It is, Graves said, no more complicated than Mother Nature.
Pipes collect manure from the barns and send it into a large, cylindrical tank that is about 20 times as large as one day's worth of manure. The digester heats the manure and breaks it down to make it easily digestible for bacteria. The acid-eating bacteria turn the sugars and amino acids into carbon dioxide, hydrogen, ammonia and organic acids. Then, acetogenic bacteria further break down the organic acids into acetic acid and more ammonia, carbon dioxide, and hydrogen. Finally, the methanogens convert the carbon dioxide into methane.
In a typical digester, one third of that methane goes to the grid. The other two-thirds is waste heat. Half of that heat goes back into the digester to keep it warm; the rest a farmer can use.
What's left is a slurry. Most digesters have a mechanical separator that divides the slurry into a liquid and a solid.
It takes 20 days for one load of manure to convert. The farmer puts a new load in every day. Maintaining the digester takes about 20 minutes a day on most days.
For a digester to work for a farmer, Graves said, he has to be creative and a good manager. Graves said Reinford is maximizing his digester. He captures the hot water that would otherwise be wasted and uses it for his home, his barns, his milk house water and even the pasteurizer he built for the milk he feeds his calves.
The solids, or fibers, left after the digestion process make excellent cow bedding, saving him the cost of sawdust. He sells some of it to other farmers and landscapers. The new and thicker bedding makes his cows more comfortable so they lay down more. Proper ventilation keeps the digested bedding in the stalls dry, which reduces bacteria growth. Lower bacteria counts earn him a higher price at the Lancaster dairy that buys his products.
Like clockwork, a truck with rotting bananas and squash shows up from the area Wal-Mart, and Reinford turns the produce into energy, and cash. Between the check from the power company and fees from Wal-Mart, Reinford said the digester earned him $200,000 last year. In 2009, when the dairy business had its worst year in recent memory, that digester carried him through.
As for the manure itself, Reinford saves there, too. He doesn't have to plow the manure under to control odor because digested manure is a liquid. He can spread it and then plant no-till corn the next day. Those who live near the fields he farms in central Mifflintown like the new manure better, too; Reinford said he hasn't gotten one odor complaint since he switched over. His soil is more intact, meaning less erosion. A few years ago, he spent thousands of dollars on commercial fertilizer that he applied to his fields. He buys none now.
Reinford is not the first farmer to extol the digester's benefits. In 1979, Gettysburg farmer Richard Waybright installed Pennsylvania's first anaerobic digester at Mason-Dixon Farms. Since then, the farm, which has 2,300 cows, has installed two other digesters.
Waybright then helped the Oregon Dairy in Lancaster County install its digester, which came online in 1985. Soon after that, the Rocky Knoll Swine Farm, also in Lancaster County, installed its digester. But momentum began building in the last decade as farmers - and just about everyone else - began thinking of ways to reduce their carbon footprint and use less fossil fuel. Reinford's oldest son, Chad, is now putting in a digester on his 440-heifer operation.
It was Reinford's middle son, Brett, who persuaded Reinford to investigate digesters in the first place. After attending college in Colorado, Brett told his father he wanted to do something with renewable energy to help the planet.
Now, Reinford and his sons are talking about starting a green power cooperative.
"Digesting is the best thing I know of anything we can do to help the environment," Reinford said. "There's just so much we can do with technology to take agriculture to the next level."
Technologies that produce energy from manure fall into two general classes: those that use heat and those that use bacteria in the process.
In scientific terms, the use of heat to produce energy from manure is a thermochemical process. The four forms include combustion, gasification, pyrolysis and torrefaction. Each is well-suited for manure that is relatively dry, such as poultry litter, because the cost to reduce large amounts of moisture in the manure is avoided. Some heat-based systems are adaptable to different scales to suit various farm settings, but vary widely in their effectiveness and cost.
Heat-based processes produce a range of potentially valuable byproducts, including liquid bio-oils, diesel fuel and combustible gas. They also produce nutrient-dense products like ash and bio-charcoal commonly referred to as biochar.
Combustion, which operates in a high-oxygen environment, produces nitrogen oxides. Because one-third of the nitrogen pollution in the Bay comes from airborne deposition, these emissions are cause for concern. In contrast, heat-based processes that reduce or eliminate oxygen (gasification, pyrolysis, and torrefaction) minimize nitrogen oxide emissions, and much of the nitrogen is emitted as inert gas.
Nutrients in the byproducts are in a dry, concentrated form, making it easier and more cost-effective to transport them out of the region.
Most heat-based processes convert much of the nitrogen to a gas that has no environmental impact.
Some systems are scalable.
Heat-based processes are well-suited for the use of dry material such as poultry litter.
Heat and energy can be used in farming operations, replacing fossil fuels and providing energy independence.
Air emissions of nitrogen, especially from combustion, may require additional treatment at additional cost.
Systems must be designed to accommodate the unique properties and variable nature of manure.
Heat-based processes are not well-suited for high moisture dairy or swine manure slurries without pre-treatment at additional cost.
Anaerobic digestion occurs when bacteria convert organic carbon in manure to methane gas. This process occurs naturally in manure lagoons and storage structures, but can be managed in a "digester" - an airtight tank or covered lagoon.
Because anaerobic bacteria require wet environments, they are ideally suited for systems fed by moist manure from cows and swine. The methane that results from anaerobic digestion is lighter than air and can easily be captured for use as a fuel to produce heat, electricity or both.
Methane can also be cleaned and fed into existing natural gas distribution systems. The capture and use of methane has an added environmental benefit - methane is a greenhouse gas with global warming potential that is 20 times higher than carbon dioxide.
From a water-quality perspective, the greatest challenge in using anaerobic digestion to produce energy is that almost all of the nutrients associated with the manure remain in the byproducts. Therefore, the liquid and solids associated with digester effluent must be treated and managed to facilitate material handling, transportation, and proper nutrient control.
The process is well-known with a long history of producing methane that generates heat, electricity or both.
The process is well-suited for high-moisture, dairy and/or swine manure slurries.
If the methane is captured and converted to carbon dioxide, a less potent greenhouse gas, the technology reduces significant amounts of greenhouse gas emissions.
If advanced separation methods are applied to the byproducts, phosphorus can be concentrated and more cost-effectively transported to areas where it is needed.
Digestion reduces the odor associated with manure, potentially expanding the potential for local application to fields where raw manure might result in complaints from neighbors.
Systems are typically not cost- effective for smaller operations - fewer than 400 cows - because the process requires a relatively large area for manure containment and can be very expensive.
Although nutrients are concentrated, most are retained in a sludge byproduct that - unless an advanced separation method is used - is not cost-effective to transport long distances.
Without advanced separation, the nutrient-rich liquid byproduct must be stored and managed as a wet nutrient source to be used as crop fertilizer on nearby fields.
From: Chesapeake Bay Commission, "Manure To Energy: Sustainable Solutions for the Chesapeake Bay Region" January 2012