Dairy manure becomes profits

Lori Tyler Gula USDA

In southern Idaho’s sprawling dairy country, cow manure has long been a costly headache for farmers and a growing environmental concern. Now, a team backed by the U.S. Department of Agriculture’s National Institute of Food and Agriculture is turning that problem into opportunity, transforming waste into fertilizer, clean water and even biodegradable plastics.

The Idaho Sustainable Agriculture Initiative for Dairy, or ISAID, has spent five years developing and testing systems that capture valuable nutrients and byproducts from manure and wastewater. The research was funded in 2020 by a $10 million Sustainable Agriculture Systems Coordinated Agriculture Project.

Idaho, the nation's third-largest dairy producer, has undergone a remarkable transformation, surpassing its 11th position just 25 years ago. However that exponential growth comes with challenges, particularly in managing the substantial amounts of liquid and solid manure generated by the dairy industry.

As a result, a team of scientists led by the University of Idaho has undertaken a groundbreaking plan to harness nitrogen and phosphorus from dairy production, converting them into valuable bioproducts. Those products can be transported and used in other areas for crop production or as raw materials for value-added products like bioplastics.

The overarching goal is to promote the adoption of transformative technologies that convert dairy manure nutrients into commercial fertilizers and value-added bioproducts. That initiative aims to enhance soil quality, sustain agricultural productivity, mitigate environmental impacts, diversify income streams and create employment opportunities.

“We’ve always known there’s value in manure,” said Brian He, associate professor of biosystems engineering at the University of Idaho and the lead on ISAID’s hydrochar project. “What we’re doing is packaging those nutrients into forms that are easy to handle, easy to apply and much more profitable than spreading raw manure on a field.”

One of Idaho Sustainable Agriculture Initiative for Dairy's most promising breakthroughs is “enriched biochar.” Researchers draw nitrogen and phosphorus out of lagoon water and the liquid left over from methane-digesting tanks, then infuse those nutrients into biochar — a charcoal-like substance. When spread on fields, it feeds plants over months rather than days, reducing fertilizer costs and runoff.

In greenhouse trials, vegetable and grain crops treated with enriched biochar grew as well as or better than those given conventional fertilizer, said graduate student Samantha Clark, who leads the biochar greenhouse studies.

Clark said, “It’s remarkable how consistent the results are. We see stronger root systems and more uniform growth, even when water is limited.”

A mobile treatment unit built by Idaho Sustainable Agriculture Initiative for Dairy partners will allow dairies to produce enriched biochar on-site starting this fall. Larger on-farm trials planned for the 2025 growing season aim to prove economic gains alongside environmental benefits.

Hydrochar locks in phosphorus

Phosphorus, an essential but expensive fertilizer ingredient, is plentiful in manure. He’s team uses hydrothermal carbonization — essentially cooking manure under pressure — to create “hydrochar,” a dry phosphorus-rich soil amendment.

He said, “At the right temperature and pressure, we can trap up to 90 percent of the phosphorus in a stable form. That cuts the risk of phosphorus washing into streams, which can trigger algae blooms, and gives farmers a reusable source of fertilizer.”

Lab-scale reactors have pinpointed optimal settings at 200 to 220 degrees Celsius and two to three megapascals of pressure. This year, Idaho Sustainable Agriculture Initiative for Dairy engineers will build a continuous-flow system designed for farm use, and economists will complete a full cost–benefit analysis.

Perhaps the most eye-catching innovation involves turning manure into biodegradable plastics. In a three-stage fermentation process led by soil and water engineer Erik Coats, bacteria consume volatile fatty acids from manure and convert them into polyhydroxyalkanoates, or PHA — a family of naturally occurring bioplastics.

Coats said, “We’re seeing conversion rates over 60 percent, which rivals industrial bioplastic facilities. And as a bonus, the process strips out extra phosphorus, so you can recover fertilizer and plastic in one go.”

Coats’ team is now fine-tuning reactor conditions to produce plastics with specific properties — from rigid packaging materials to flexible films. A life-cycle analysis is underway to compare the manure-based PHA footprint against conventional plastic production.

Water treatment is another pillar of Idaho Sustainable Agriculture Initiative for Dairy's work. A prototype system dubbed the “Clean Water Machine” combines sedimentation, membrane filtration and advanced chemical treatments to purify nutrient-laden wastewater. The result is water clean enough for crop irrigation -- and, with extra polishing steps, potentially even for human consumption.

Lisa Martinez, Extension engineer, said, “Dairies use huge volumes of water, and disposing of manure-rich wastewater is a major expense. This system could let farms recycle up to 80 percent of their process water, cutting costs and protecting local waterways.”

Idaho Sustainable Agriculture Initiative for Dairy constructed a mobile lab trailer to test two parallel filtration lines on working dairies. Field trials began in early 2024, with performance data being collected through 2025.

Taken together, the technologies paint a picture of a circular dairy bioeconomy, one in which nearly every component of manure and wastewater is recovered and reused. That approach promises multiple benefits -- healthier soils, fewer greenhouse gas emissions, new revenue streams and cleaner rivers.

Jason Winfree, an agricultural economist with the University of Idaho who is leading Idaho Sustainable Agriculture Initiative for Dairy's market analyses, said, “Imagine a dairy where you produce milk, sell biochar, sell phosphorus amendments, sell bioplastics and reuse your water. That could radically change the financial outlook for family farms.”

Undergraduate and graduate students in agriculture and business programs have drafted business and marketing plans for all three product lines. Their work explores supply-chain logistics, potential markets and price points, laying the groundwork for spin-off companies in rural Idaho.

Local producers say they’re eager to see the technologies on their home farms. Third-generation dairy owner Hank DeVries, whose family has run a 1,200-cow operation near Buhl for four decades, called the research “a game changer.”

DeVries said, “We’ve spread manure for years, but this could be a whole new industry born from milk production. Clean water, better fertilizer and maybe even plastic — it’s like turning waste into gold.”

At nearby Sunnyside Dairy, co-owner Jason Nunes agreed.

Nunes said, “Manure is a renewable resource. If we can turn it into high-value products, that’s good for our business, good for the environment and good for the public perception of dairies.”

Idaho Sustainable Agriculture Initiative for Dairy's outreach arm is already in motion. Extension specialists have produced bulletins and online tutorials, and they launched “The Clever Cow,” a podcast series that walks listeners through each technology.

A national “Waste to Worth” conference, co-hosted by Idaho Sustainable Agriculture Initiative for Dairy and the U.S. Department of Agriculture, convened in Boise in spring 2025. The event brought together engineers, economists, regulators and producers to share lessons learned and build partnerships for commercial deployment.

With on-farm trials, economic assessments and environmental monitoring scheduled through 2025, Idaho Sustainable Agriculture Initiative for Dairy researchers say they will soon have the data farmers need to decide whether to adopt the new tools.

Winfree said, “If the numbers add up, it won’t be a question of ‘Should we?’ but ‘How fast can we get started?’”