Grass to Gas

Grassland and perennial biomass streams are being tapped for conversion as supplemental feedstock in anaerobic digesters. These streams are considered in the biogas market for their environmental benefits, high-yielding rates and reliability.
By Katie Fletcher | February 03, 2015

Anaerobic digesters (AD) are usually fed manure or food waste, yet other options are being tested and used in the biogas industry. On the expanding menu of feedstock possibilities are crops grown specifically for the purpose. Research conducted in Ontario, Canada, at the University of Guelph Ridgetown Campus explores the possibility of growing perennial energy crops and native grasses for biogas production. Energy crops are being considered in the biogas market for their environmental benefits, high-yielding rates and reliability.

The U of G-Ridgetown teamed up with New Energy Farms and Seacliff Energy for a project exploring energy crop potential in biogas production. Right now, the focus is on the methane yield at lab level, but the hope is to eventually test perennial feedstock crops in a 250-kW digester located at a campus research facility. “The main takeaway of the things we’ve tested so far is that some of them provide really high yields in the field, but they don’t convert very easily to biogas,” says Brandon Gilroyed, assistant professor School of Environmental Sciences at the U of G-Ridgetown. “We need to, for our future research, place more emphasis on pretreatment and things like that to unlock more of that energy.”

Paul Carver, CEO of New Energy Farms, says, “We identified a need for perennial biogas crops for a number of reasons.” NEF is involved in providing suitable cultivars of different energy crops, established through its CEEDS system and production testing. The Crop, Expansion, Encapsulation and Delivery System, creates a proxy for seed in vegetative crops, such as miscanthus, napier grass and arundo donax. The system was developed to make planting energy grasses and other vegetative crops as simple as conventional arable crops. “In areas where biogas projects have expanded rapidly, such as Germany, there is now saturation of annual biogas crops on arable land,” Carver says.

Germany has been using predominantly corn silage, among other streams, for biogas production. The plants that NEF is exploring are suitable for nonfood-quality land, which subsequently allows new plantings to occur without affecting food production. Another contributing factor to energy crop implementation is that biogas byproduct disposal requires a land base. “Sites with perennial crops on them for 10 years or more create a good logistical system for this recirculation of nutrients,” Carver says.


The last factor resides in the fact that new biogas projects need secure sources of feedstock. A proportion of perennial grasses can provide feedstock for 10 years, according to Carver. Crops like these usually take time to establish, however. “I think there will be some ways of dual cropping, or things like that, to help with those initial establishment years, but that is an issue for sure with the whole concept,” Gilroyed says.

Presently, most in the space see energy crops’ role in the production of biogas as supplemental; a side choice to the main dish on the menu. NEF believes the menu should have a variety of sides suitable for biogas and different growing conditions. “These would be crops like napier grass, arundo donax and miscanthus, which support production from Canada down to Florida,” Carver says. “We have also found that some of the energy crops have a much wider harvest window, and so improving the logistics of the feedstock supply. With this range of crops it would be possible to get year-round supply.”

A sustainable feedstock supply is crucial for biogas producers. “A big part of the impetus for us looking into it is the biogas market right now; it’s really hard to find high-quality feedstocks,” Gilroyed says. “There is so much competition, and if we want to see this sort of model work at the farm-scale, so smaller digesters, I think that they’re going to have to have some options where they are able to independently create at least a portion of the diet they feed, because the volatility is too much to handle.”


Perennial energy crops and grasses have the added opportunity to generate cellulosic renewable information numbers (RINs). The U.S. EPA announced in July a final rule for the renewable fuel standard (RFS) program that expanded pathways for biogas-based fuel to help boost cellulosic and advanced fuel numbers. Allowing biogas transportation fuel pathways to generate RFS cellulosic credits brings opportunity for further biogas project development. NEF’s collaboration with the U of G-Ridgetown and Seacliff is not upgrading the biogas to transportation fuel, but NEF recognizes the opportunity it presents. “We see a very strong growth potential for this area as biogas can be used for heat, electricity and road fuels,” Carver says. “We feel there is a substantial commercial opportunity to apply the high-yield perennial grasses to this market.”

One project under development in Missouri will create biogas-based fuel. Roeslein Alternative Energy LLC is developing and constructing the project in collaboration with Murphy-Brown of Missouri LLC, the livestock production subsidiary of Smithfield Foods Inc. The goal of the $80 million project is to produce 50 million diesel gallon equivalents by the end of the decade using biogas derived from hog manure, energy crops and cover crops harvested between growing seasons. “This project can be a model to show how both economic and environmental benefits can be gained by using manure in a different way," says Rudi Roeslein, president of RAE and CEO of Roeslein & Associates.

The project will not only clean and compress biogas for transportation fuel, but will help with efforts to replant and restore native grassland and prairie on marginal land.


Roeslein Northern Missouri Real Estate has been restoring land with grassy prairies on it’s 1,600-acre farm located within the project area.  Already 400 acres of prairie has been planted that could be used for testing the potential feedstock.

The massive project is being implemented in phases. The installation of high-density polyethylene covers on an initial 19 lagoons at MBM’s Valley View and South Meadows farms in Northern Missouri is complete. The biogas that rises to the top of the lagoons will be collected for further conditioning, while the leftover indigestible solid residue can be used as a natural fertilizer, and water can be safely used for irrigation. "There is value in the gas we capture as alternative vehicle fuel,” Roeslein says. “There is even more value to the environment from reduced greenhouse gas emissions, eliminating rainfall effects on treatment systems and odor reduction."

Next on the project timeline is installing biogas cleaning and conditioning equipment to produce renewable natural gas (RNG), and establishing a network of distribution centers to provide the RNG to vehicle fleets. The project has the potential to create several hundred million cubic feet of RNG annually for regional distribution. RNG production is slated to begin this year. The third phase includes a demonstration of using aboveground AD systems to process a combination of manure and perennial feedstocks.

Now that biogas-based transportation fuel projects can sell either advanced biofuel or cellulosic compliance credits, an increase in project development in the U.S. biogas industry may become apparent. Grassland and perennial crop establishment has a developing market opportunity with biogas, and potential to become an appealing, high-yielding and reliable side choice for producers.

Author: Katie Fletcher
Staff Writer, Biomass Magazine
kfletcher@bbiinternational.com
701-738-4920