Kentucky farmer turns poultry manure into profitable power and fertilizer
As if owning and operating eight chicken barns wasn’t enough, Campbellsville, Kentucky farmer John McLean is turning waste into wattage – literally.
McLean owns two anaerobic digesters that can generate electricity or heat and transportation fuel. As a byproduct, the digesters also produce a nutrient-rich fertilizer substance for his crop fields.
McLean’s secondary digester can hold 2.5 million gallons of material, while his more sophisticated primary digester holds 270,000 gallons. Surprisingly, he doesn’t have any trouble keeping the digesters “fed.”
“In addition to any excess chicken litter that we may have, we have a permit to take non-human waste, including feedstocks from corporations with food waste,” McLean explains. “We don’t accept scraps, because we don’t currently have a separator to remove plastics, which are non-biodegradable.”
A way to cut costs
McLean’s says that when he first got his chicken barns up and running in 2003, one of his biggest expenses was energy.
“When I saw how much energy, how many BTUs, the broiler houses use, I immediately tried to find ways to cut costs.”
After a great deal of research, he started construction of his first digester in 2011.
“I served as the general contractor on this job,” he says. “I wanted to have my hands on it from day one.”
Since then, McLean says he has learned a great deal about anaerobic digesters.
“Eighty to 90 percent of what I’ve learned about digesters has been learned by trial and error,” he says. “Digesters are expensive, and they are usually invested in by a large corporation and run by an employee. That employee doesn’t have near the stake in the success of the operation as I do.”
The right diet
McLean says digesters are fairly common in New York, Wisconsin and California due to their large dairy operations but added that all digesters (and all waste fed into them) aren’t the same. His digester was “inoculated” with bacteria from another digester that uses poultry litter.
“There isn’t a website or catalog you can go to and order up the perfect blend of bacteria to digest what we are putting through this system,” he says. “Plus, we practice co-digestion, which means we digest both litter and feedstock (food waste).”
He’s quick to point out that in order for anaerobic digestion to happen, the right environment has to be created and maintained.
“The digester is kind of like a stomach,” McLean explains. “You have to feed it just the right diet for things to work correctly.”
The particular blend of bacteria he’s using works best on a low-protein “diet,” he says, and digests large quantities of simple sugars and oils.
“This is the only one of its kind in the state that I know of that digests animal waste,” he said. “And even though we sell two thirds of our chicken litter, having eight houses produces a great deal of waste.
“Add in that Kentucky has a lot of food waste, and there is a market for the service that a digester provides. Everything that goes into that digester turns into renewable, sustainable, green energy and fertilizer, and it doesn’t go into a landfill.”
McLean is quick to say that being pro-renewable energy doesn’t make him anti-coal.
“Living here in Kentucky, I know that we have a lot of coal miners, and coal has been financially good for our state. There’s room on the grid for energy made from all kinds of processes.”
How the system works
Photo 1
In Photo 1, the black plastic bubble that resembles a pillow is the secondary digester, which works most efficiently in the summer months, when temperatures are high, accelerating the digestion process.
Photo 2
In Photo 2, the green grain bin-like structure is the primary digester, which works steadily all year round.
The digesters’ action creates biogas, which is captured and fed through the pipes. The gas is then “scrubbed” to remove impurities before it enters the generator.
Photo 3
Photo 3 shows the generator. Electricity comes out of the generator and goes through a switch gear, which synchronizes it back to the power grid. McLean sells the energy created to East Kentucky Power.
McLean has installed numerous required safety features to protect linemen and other workers.
“If the grid goes down, it shuts my generator down,” he says. “Working together, we’ve made sure that we won’t be pushing energy to the grid in case of downed lines.”
Bonus fertilizer
The process of creating power also produces a substance that can be used as crop fertilizer.
“That’s the good stuff,” McLean says.
Called digestate, the liquid left over after the gas is separated is incredibly nutrient-dense.
“We’ve tried different methods of application,” he says, but found that injecting it straight into the soil is best.
This method virtually eliminates the smell. We’re currently doing trials here on our farm. We plan to sell the digestate at some point, but we are doing some field trials this growing season to see how much better the digestate is than regular chicken litter.”
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