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How to get the good stuff out of chicken manure

Environmental engineers look for sustainable ways to deal with the waste in Maryland

by Michael Torrice
April 18, 2016 | A version of this story appeared in Volume 94, Issue 16

A farmer uses a loader to move chicken manure on farm.
Credit: Edwin Remsberg/VWPics/Newscom
Moving manure in a Maryland chicken house.

Lee Blaney tells people he has the best-smelling lab on the campus of the University of Maryland, Baltimore County (UMBC).

He’s joking. The environmental engineer and his team operate reactors bubbling with slurries of chicken manure that give off a stinky ammonia odor.

“Once you get used to it, it’s really not that bad,” Blaney says. “But probably only people who deal with a lot of crap get used to it.”

Blaney and his students willingly live with this stench because they see a resource trapped in the smelly waste.

At last month’s American Chemical Society national meeting in San Diego, Blaney’s graduate student Utsav Shashvatt reported on the group’s process to extract phosphorus from chicken litter, the dry, dirtlike mixture of manure and other debris farmers scrape from the bottom of their chicken houses.

By pulling phosphorus out of the manure, the researchers hope to provide a sustainable source for the agriculturally vital nutrient. The technology is one of several approaches environmental engineers are working on to help Maryland chicken farmers turn their manure into valuable products while also responding to regulations designed to improve the water quality in the nearby Chesapeake Bay.

For decades, the Chesapeake has suffered from low-oxygen, or hypoxic, dead zones, which are uninhabitable for crabs, fish, and other native species. These dead zones are largely caused by nutrient pollution—nitrogen and phosphorus—that washes off the land and into waterways that feed into the Chesapeake, says Bill Ball, the executive director of the Chesapeake Research Consortium, which coordinates and communicates research on the bay. A large portion of this pollution comes from agricultural lands. Just as these nutrients help crops grow on farms, the compounds fuel the growth of algal blooms in the bay. When these algae die, bacteria consume them, using up the water’s dissolved oxygen and creating the dead zones.

Chicken manure contributes to the bay’s nutrient pollution. Farms on the Delmarva Peninsula—which forms the bay’s Eastern Shore and consists of most of Delaware and parts of Maryland and Virginia—raise more than half a billion chickens per year and produce millions of tons of manure, Blaney says. “The easiest thing to do—and what has been historically successful—is to use that litter as fertilizer,” he says. In fact, many farmers see the manure as a valuable resource that they can apply to their own fields or sell to others.

But when chicken litter is used as fertilizer, it’s easy to add more phosphorus to soils than crops need, Ball says. Compared with other manures, such as those from cows and pigs, poultry litter contains a relatively high ratio of phosphorus to nitrogen. “Because the manure is cheap and farmers have to get rid of it, they often end up overapplying phosphorus,” Ball says. When oversaturated with phosphorus, soils can start to leach the nutrient into nearby waterways.

Last year, Maryland instituted regulations that could significantly restrict farmers’ use of chicken litter. The regulations, called the Phosphorus Management Tool, are part of the state’s plans to curtail nutrient pollution flowing into the Chesapeake. Maryland, along with the District of Columbia and the other five states—New York, Pennsylvania, West Virginia, Delaware, and Virginia—with waterways that drain into the bay, must develop plans to meet nitrogen and phosphorus limits set by the Environmental Protection Agency under the Clean Water Act.

When the new regulations are fully implemented in 2022, the amount of phosphorus farmers can apply to their fields will be restricted, in part, by how much of the element is already in the soil.

This could create manure problems for farmers such as Lee Richardson. On his farm in Wicomico County, Md., Richardson raises chickens—about 175,000 broilers at a time in six houses—and grows corn and soybeans on 2,000 acres of land.

More than half of the farms in the lower part of Maryland’s Eastern Shore, where Wicomico is located, have soil phosphorus levels that would trigger the new regulations. And about 10% are already prohibited from applying phosphorus because of excessively high soil levels.

Based on the new regulations and his farm’s soil levels, Richardson says by 2018 he might not be able to add more phosphorus to his fields.

So farmers like him will have to find a way to get rid of their chicken litter. One solution is to truck it out of the Eastern Shore to farmers with land that can still take phosphorus. Although the state runs a program that helps with manure transportation costs, Richardson says it can get expensive.

Blaney thinks his team’s solution could be another option for farmers. Nitrogen and phosphorus make up just a tiny fraction of the mass of chicken litter. So most of what is shipped by farmers—and what contributes most to transportation costs—lacks the nutrients that farmers want.

Pulling out the good stuff
A schematic depicting a process to extract phosphorus from chicken litter.
Credit: Adapted from Lee Blaney (schematic); Lee Blaney (photos)
To extract phosphorus from chicken litter, engineers add a slurry of the manure to a reactor and bubble in CO2 to drop the pH to about 5. This releases ammonium and phosphates into the water, which is then pumped into a second reactor. There, the engineers add sodium hydroxide and air to increase the pH to 9 to precipitate out struvite and other phosphate minerals. The remaining liquid can then be recycled into the first reactor to make the slurry for the next batch of manure.

By extracting the phosphorus from the manure, “we’re not pulling out much of the actual mass of the poultry litter—no more than 5%,” Blaney says. “But we’re pulling out the good stuff.” Those nutrients would be valuable for other farmers needing phosphorus for their crops, and would be in an easier and less expensive form to ship.

The extraction process takes place in two separate reactors and starts with a slurry of the poultry litter. In the first reactor, the engineers bring the slurry’s pH down to about 5, which releases ammonium and phosphates from the manure and into the water. The liquid is separated from the remaining solid and pumped into the second reactor. There, the team increases the liquid’s pH to about 9, which causes the end product, phosphorus-rich minerals, to precipitate out.

In their lab-scale tests, the engineers can recover between 80 and 90% of the phosphorus in a litter sample. Mostly, the team produces an ammonium phosphate mineral called struvite (MgNH4PO4•6H2O), which can serve as a slow-release fertilizer for crops. But they also precipitate out a calcium phosphate mineral (CaHPO4) that could be used as a nutrient supplement in animal feeds.

And the solid leftover in the first reactor isn’t just waste. It is still rich in organic matter, making it useful as a fertilizer that farmers could apply to fields without worrying about adding to their phosphorus levels. Blaney says the material could also be used in anaerobic digestion, a process that uses microbes to break down organic matter to produce biogas, a mixture of methane and carbon dioxide that can be burned as fuel.

Other phosphorus extraction methods already exist, including ones to pull out the nutrient from wastes such as biosolids leftover after wastewater treatment. But, Blaney says, those processes are often energy-intensive and require the addition of magnesium and ammonium to produce minerals.

To make this process sustainable, Blaney and his team want to minimize the amount of water and chemicals required. When the engineers analyzed the composition of chicken litter, they realized that it had all the elements they needed to form struvite. So the only additions they make are in the steps to acidify the slurry and precipitate the minerals. “What we really wanted to do was to find how to best utilize the full chemistry of the raw poultry litter,” Blaney says.

For the acidification step, the team decided to skip strong acids, which Blaney says would add to the cost of the process. Instead, the researchers bubble carbon dioxide into the manure slurry. To increase the pH in the second reactor, the engineers add sodium hydroxide and bubble in air to push out any residual CO2.

To reduce the water they use, the researchers pump out the liquid remaining in the second reactor at the end of the process and use it to form the slurry for the next manure batch. They can recycle the liquid through 10 cycles and still recover greater than 80% of the litter’s phosphorus.

Stephanie A. Lansing, an ecological engineer at the University of Maryland, College Park, says the extraction method is one way to increase the sustainability of chicken farming. Farmers import feed onto the Eastern Shore for their chickens, she says. “A portion of that comes out in the manure. But those nutrients stay on the shore and don’t necessarily go back to where the feed is grown.” Extracting the phosphorus and shipping it back to the feed growers could help close that loop.

Lansing is also working on other uses for chicken litter. She’s developing two technologies that turn the manure into energy. The first uses anaerobic digestion to produce biogas, and the other gasifies the manure into syngas, a fuel consisting mostly of hydrogen and carbon monoxide. Her group has demonstrated the technologies at multiple scales—from lab to farm scales.

Blaney is working with Triea Technologies, a small Maryland agricultural technology company, to translate his team’s extraction process into an on-farm system. He hopes to have such a system running on Richardson’s farm in Wicomico within the next year.

Richardson sees the extraction technology as a win-win situation for farmers. “If they can make it economical and I can get the by-products back—the organics and minor elements—it solves two problems: Me not losing my manure, and making the state happy with no phosphorus going on the field.”

For Ball, whether it’s converting chicken litter into an easy-to-transport fertilizer or a gaseous fuel to be burned, finding other uses for the manure will certainly help the water quality in the Chesapeake watershed. “A good solution,” he says, “would be one that is economically beneficial and is better than applying it to the land.”  


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