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Waste Solutions: From Farm Waste to Feed, Fertilizer and Energy

Waste lagoon and hog houses

NC State University develops and delivers waste solutions that benefit farmers, consumers and the environment. Learn about ways that extension specialists and researchers are helping farmers use plant-based agricultural leftovers as cattle feed and turning hog waste into valuable bioenergy and fertilizer.

Waste Solutions: From Farm Waste to Feed, Fertilizers and Energy
Episode 13: Farms, Food and You Podcast


Dee Shore (00:07):

Waste management is part of doing business for North Carolina’s 46,000 crop and livestock farms. And at North Carolina State University, researchers and extension specialists are working to cut waste management costs, create income from value-added products, and protect the environment.

I’m Dee Shore, and in this episode of Farms, Food and You, we consider two ways that the university is working to deliver waste management solutions.

One involves using plant-based agricultural leftovers to feed some of the state’s 800,000 head of beef cattle, and the other entails turning hog manure into fertilizer and renewable energy.


Dee Shore:

Cows are amazing creatures. Having a stomach compartment called a rumen allows them to derive nutrients from a host of plant-based materials that humans, pets and many other animals can’t digest. As North Carolina State animal scientist Matt Poore explains, farmers have known this for a long time.

Matt Poore (01:18):

For eons, millennia, cattle and other ruminants have been used as a way of finding a niche within a farm to use products that cannot be used by humans directly but that can be converted into meat, milk, and that sort of thing. So this is a practice that goes back all the way to domestication.

Dee Shore (01:37):

Our knowledge of the range of what cows can digest has grown. When Poore began working as an extension specialist at NC State 30 years ago, cattle were fed supplementary corn and soybean meal. But slowly, Poore says, researchers began finding that the meal-making process could yield more high-quality cattle feed. The key: leftover soybean hulls.

Matt Poore (02:02):

We started doing feeding trials, and we found that there was absolutely no difference in the performance between animals fed a supplement of soybean hulls versus a supplement of corn and soybean meal. And actually the cost difference was very dramatic. We were paying 40% of what the other feed was.

Dee Shore (02:20):

Now, soybean hulls are a standard feed ingredient, and they’ve risen in price. So farmers have turned to other options, things such as corn gluten, a byproduct of soft drink manufacturing, distillers grains from making ethanol, sweetpotato skins, pumice from apple cider production, bread from bakeries and even unsold pumpkins.

Recently, Poore and Deidre Harmon, an NC State animal scientist based at the Mountain Research Station in Waynesville, have been working with beef cattle farmers and cotton gins to make use of leftover cotton seed.

Matt Poore (02:58):

We have an increase in our cotton crop in the state and whole cottonseed is an interesting feed because it doesn’t even look like feed. It looks like a tip of a Q-tip, if you had to describe it somehow. And what we know is that seed contains protein and fat and it’s got some fiber there. And actually it turns out that the very best use for that is to feed the cows as a supplement.

And so we have funding right now from the North Carolina Agricultural Foundation to better explore the value of that feed and how it might be utilized in diets for cattle and whether or not processing it in any way may improve it. Traditionally, we’ve taken it and crushed it and extracted oil and created other products from that, but the oil mills that used to be abundant across the South are now gone. That has dramatically increased the availability of cotton seed.

Dee Shore (03:52):

Harmon adds that cotton seed isn’t the only material from cotton plants that can be used for cattle feed.

Deidre Harmon (03:59):

There’s some cotton lint and leaves and parts of that plant that actually falls out of that ginning process that we can actually take and utilize. It’s a great hay supplement or a replacement for hay. And back two years ago when we had several hurricanes that impacted North Carolina, we actually had several producers that lost their hay crop. And so they replaced that hay with cotton gin byproducts.

There’s a lot of different examples of byproduct feeds that come from different industries that we have here in North Carolina. And without having some of that research and being able to utilize it in beef cattle, most of that byproduct would probably go to a landfill.

Dee Shore (04:38):

These byproduct feeds also provide cattle with protein and energy that hay or grass may not have in high enough levels for cattle to thrive. Poore says there are other benefits as well.

Matt Poore (04:51):

It gives value to the industry that is producing the byproducts. The demand from cattle, for example, is helping support the price of cotton seed, which goes back to cotton farmers. Furthermore, having an inexpensive supplement encourages the farmer to do a better job nutritionally with his cows, which is better for their welfare, and also produces a better-quality meat product down the line.

And if you can go buy your supplement from a local business and it’s locally produced, that money that you pay stays in the community. It’s the same concept as local foods. So it’s benefiting the individual financially. It’s benefiting the ag industry in general because of supporting price of our products. And it’s helping all consumers through improved beef quality.

Dee Shore (05:36):

The use of agricultural byproducts as feed clearly benefits cattle, farmers and agribusinesses. NC State faculty members are also finding ways to turn other farm wastes into treasures. A good example,:hog waste. North Carolina ranked second among the states in hog production, an industry worth about $3 billion annually. But farmers have faced significant challenges when it comes to public concerns about odors and the potential flooding risks associated with the lagoon-based waste treatment system used on the state’s hog farms.

Agricultural engineer Jay Cheng joined NC State 23 years ago, and since day one, he’s been tasked with finding swine waste management alternatives. Right now he and animal scientist Eric van Heugten are evaluating a waste digesting system that turns manure and plant-based farm waste into two usable commodities, bioenergy and organic fertilizer. Holistic Farming Incorporated has supported the research. The company is owned by Jason Shih, a former NC state faculty member and expert in anaerobic digestion for biogas production.

In the conventional lagoon system, hog farmers use water to wash swine waste out of hog barns and send the resulting mixture into a lagoon. From there, the mixture breaks down and settles into two layers, a sludge at the bottom of the lagoon and a liquid layer at the top that is sprayed onto crop land. The system Cheng and van Heugten are testing is much different.

Jay Cheng (07:17):

In this new project, we do not wash. We don’t add additional water. We just scrape the swine manure and then send that into our digester. Another difference is that in this new project, we have a two-stage digestion. The first stage is that we have the hog manure. And through the digestion, we got biogas, and we can use the biogas to generate bioenergy.

And we also added what we call second-stage digestion, where we take the treated water after digestion. We separate the solids and the water with a lot of nutrients, nitrogen, phosphorus, potassium, and the other minerals. Then in the second digester, we put that water in and we also add agricultural residues. For example, we can add corn stover, or we can add the grasses. The good thing about that is that adding agricultural residues will suck the nutrients and the water after the primary digestion.

It’s not a completed digestion of the agricultural residue. And after partial digestion, the product from the agricultural residues become an organic fertilizer.So in other words, in this new project, we have two products. One is the biogas that can be used for energy generation. It is a good energy. It’s renewable. It’s green energy. So that’s one benefit. Another benefit is we can also generate the organic fertilizer.

Dee Shore (09:07):

The system has shown promising results in laboratory and pilot-scale experiments. Using high temperature digestion makes the fertilizer pathogen-free, and adding agricultural residues to the waste material raises the rate of biogas production. But for now, there’s a hurdle standing in the way of widespread commercial adoption. The hurdle is one that many other waste management technologies haven’t crossed, and that hurdle is cost.

The potential return on investment for the new system hasn’t been studied yet, but it does offer cost advantages over larger digestion systems that have come before. Similar systems to produce biogas from animal manure are popular in Europe, but Cheng says the situation in Europe is much different than it is in the United States.

Jay Cheng (09:58):

The difference between U.S. and those European countries is that our energy price is much lower. For example, in Germany, their electricity price is about 30 euro cents per kilowatt hour. Ours is like from seven to eight U.S. cents per kilowatt hour. Their electricity price is several times of ours. In other words, the farmers can get some profit out of selling electricity generated from the biogas, which is produced from the treatment of the manure. Of course, in Europe, the government also will provide the subsidy to this kind of practice.

Dee Shore (10:47):

Subsidies in the U.S. may or may not be the answer. And so Cheng continues his quest for a cost-effective system with a good rate of return on investment for farmers, and he encourages farmers and others to work together toward waste management solutions.

Jay Cheng (11:04):

I know if we can develop a new technology which is much cheaper than the current lagoon system, obviously everybody’s going to convert. Unfortunately, we have not found the silver bullet. To get there, we have to work together – the government, farmers, environmental groups and the researchers. We all have to work together to make our future better.


Dee Shore (11:37):

Thanks for listening today, and we hope you’ll join us again for the next episode of Farms, Food and You. To learn more about the College of Agriculture and Life Sciences and our podcast, visit While you’re there, share your thoughts. We’d love to get your ideas and to hear what topics you’d like for us to explore in the future.


Our Guests

For 30 years, Matt Poore has served as a professor and beef Extension specialist at NC State University, where he focuses on nutrition for beef cattle, sheep and meat goats. He grew up spending his summers in North Carolina and his winters in the western part of the country. He often wondered why cows in North Carolina seemed to be merely part of the landscape, while in the West they were big business. The contrast captured his interest, and so he decided to study animal science and nutrition. At Arizona State University, he earned bachelor’s, master’s and doctoral degrees in the field.

Deidre Harmon has worked at NC State for three years as an assistant professor and extension livestock specialist stationed at the Mountain Research Station in Waynesville. She grew up on a cow-calf farm, where she enjoyed feeding the cows and seeing how nutrition influenced the kinds of calves the cows produced. She holds bachelor’s degree from Virginia Commonwealth University, a master’s from Virginia Tech and a doctorate from the University of Georgia.

Jay Cheng is a professor of biological and agricultural engineering at NC State University, with a primary focus on research and teaching related to environmental engineering and bioenergy processes. He has engaged in research collaborations around the globe and holds three engineering degrees: a bachelor’s degree from Jiangxi Institute of Technology in China, a master’s from Saints Cyril and Methodius University in North Macedonia and a Ph.D. from the University of Cincinnati.