Verbio North American plant converts cornstalks to natural gas

Chris Kick and Kapil Arora
Iowa State University Extension and Outreach
Bale of corn stover.

One of the state’s most abundant resources — corn "stover" — is being used to create renewable natural gas that heats Iowa homes and businesses. 

As of Dec. 7, the Verbio North America plant in Nevada, Iowa, has been converting chopped cornstalks into natural gas that enters an Alliant Energy pipeline that traverses central Iowa. 

Using anaerobic digestion, eight large digesters combine the corn stover with the bacteria of livestock manure, which results in the conversion of corn residue into biomethane gas that is equivalent to the natural gas found in fossil fuels. 

The plant, known as Verbio Nevada Biorefinery, is in its beginning stages with plans to expand in the coming months, with a goal of providing enough renewable natural gas to heat 5,000 homes. Eight additional digesters are being built, with plans to build an additional eight, as the company begins to produce corn-based ethanol. 

“Stover is basically aboveground plant material of the crop, other than the grain,” said Kapil Arora, field agricultural engineer with Iowa State University Extension and Outreach. “It can be chopped into different sizes, depending on the needs of the plant, and it can easily be made into bales.” 

Iowa is the nation’s leader in corn production — with over 13 million acres and over 2 billion bushels harvested annually. After the corn is harvested, the stover is what is left behind to decompose on the ground. 

Also called corn fodder or crop residue, the stover is nutrient rich but also poses a challenge for farmers when they go to plant the following year’s crop. 

“Farmers here in Iowa, as the yields have gone up, are faced with additional stover left on the field, and many do additional tillage just to get that stover to decompose and degrade,” said Arora. “There has been a need to do something with that stover for many, many years.” 

Arora and ISU Extension and Outreach have been involved with Verbio from the start, providing technical support, hosting farmer meetings and conducting research. 

The process 

After the corn is harvested, Verbio employees condense the stover on contracted fields into large square bales that are easy to move and stack. Verbio typically removes about 50% of the corn stover, which reduces the need for tillage and allows some farmers to pursue no-till planting by reducing the amount of residue left on the surface. 

Farmers are paid $8 per bale and the equipment and labor are supplied by Verbio. The company contracted about 6,000 acres this year and hopes to expand to 30,000 acres in 2022. 

The end result is a renewable source of energy with multiple environmental benefits. 

“We’re taking the carbon degradation that would go up into the atmosphere, we’re capturing that, we’re scrubbing it and we’re allowing you to heat your home with it locally,” said Ron DeJongh, president of Verbio Agriculture. 

The bales go through a hammer mill and are chopped to less than 1/4 inch size to create the most surface area possible, before being fed into digesters that are full of manure and bacteria that decompose the stover and create biomethane gas.  

Gas coming off the digesters is scrubbed and concentrated to almost 99.9% biomethane, before being pressurized and pushed into an Alliant Energy pipeline in front of the plant. The plant plans to eventually become energy sufficient, burning its own gas to run various plant operations. 

The process is fairly simple. But perfecting it and making it economical has taken time. 

Background 

Verbio bought the plant from DuPont about two years ago. Original plans were to produce ethanol from the stover, but those plans did not come to fruition. 

The new owners hope to continue the progress that was made, and have plans to decommission the stacks of old bales of corn stover left behind by the previous owner. 

Working with ISU Extension and Outreach, Verbio is improving its process and plans for growth. 

According to Arora, who has studied corn stover for many years, Iowa has the potential to support additional corn-stover plants across the state. He predicts more plants will be built across the Midwest, as well. 

“Traditionally we have taken energy from fossil fuels, which are buried deep in the soil, underneath the earth’s crust. But this methodology basically takes carbon on the surface of the earth and cycles it into a fuel, and eventually we will be going down this path more and more,” Arora said. 

Looking ahead 

Arora is helping the company study logistics and engage with Iowa farmers and the public. Farmer meetings were held during the summer of 2021, and more will likely be held next year. 

He also sees opportunities for student researchers, who may complete field research related to corn stover, or possibly work for Verbio as an intern or employee. 

“There’s a big, long-term relationship getting started here and I envision that as they grow into this space, we will continue to have a significant role to play with Verbio,” Arora said. 

When fully operational, the Nevada plant plans to process about 100,000 tons of corn stover a year.  

In addition to natural gas — the primary product — the process yields a nutrient rich byproduct called humus, which serves as a soil amendment and organic fertilizer.