Boosting Biomass for Bioenergy

Many dedicated energy crops hold promise as feedstocks for next-generation ethanol. Extensive R&D is still needed, however, to overcome the challenges in making these plants viable for commercial applications.
By Katie Fletcher | September 22, 2014

The bottom line is that there’s no such thing as a one-size-fits-all energy crop. “Some of these have a longer history of research behind them, like switchgrass and poplar, so there is more to go on, but we are always looking for new crops that might fill the niche,” says Cathy Ronning, program manager at the U.S. DOE, adding that the agency isn’t placing its bets on any certain crop.

This year, $12.6 million was awarded to 10 projects developing new cultivars of regionally adapted bioenergy feedstock crops, and in researching the complex interactions between bioenergy feedstock plants and their environment. A number of them build on existing knowledge of some of the dedicated energy crops with cellulosic ethanol feedstock potential including sorghum, switchgrass, poplar and miscanthus.

The 10 projects were selected through the DOE-USDA Plant Feedstock Genomics program, which was created in 2006, combining the DOE’s know-how in genomic sequencing and biofuel production analysis and the USDA’s experience in crop improvement. The program supports the fundamental research of these energy crops for bioenergy production. “In the past few decades, there has been tremendous advances in genomics and systems biology approaches,” Ronning says. “We believe we can use these technologies to speed up the development of these plants in a sustainable and adaptable manner to produce feedstock plants that require fewer inputs, specifically like fertilizer and water.”

Seeking Sustainability
Dedicated energy crops naturally produce more biomass per acre and require less fertilizer, water and other resources than annual field crops. Many can grow in less than optimal conditions with little management, using only marginal lands to retain land for food crops.

Some farmers are hesitant to plant the crops, however, because of unfamiliarity with growing practices for existing varieties. Also, the logistics of harvest, transportation and storage for large-scale commercialization of dedicated energy crops has not been fully worked out for commercial-scale biorefineries. Ultimately feedstock is the single largest cost driver for biofuels and, in many cases, the main barrier to cost competitiveness and scalability.

Genera Energy Inc. is a company focused on managing this supply chain with various producers and developers to overcome challenges like scalability. “Some can take a wide range of feedstocks on any given day, others are more restrictive, and balance is needed of all the agriculture concerns upstream with downstream technology provider requirements on their technology,” says Sam Jackson, vice president of business development with Genera Energy.

Ceres Inc. also works to improve commercial development with product lines and development programs for high biomass sorghum, sweet sorghum, switchgrass and miscanthus. “We have collaborated with a number of industry participants involved in cellulosic biofuels and biopower production,” says Gary Koppenjan, communications director with Ceres. “These tests have confirmed that biomass from our energy grasses can be converted and processed into various fuels or biobased products, and have provided data we have used to further enhance our energy crops for use with these conversion technologies.”

Sorghum’s Scalability
John Mullet, a professor at Texas A&M University, College Station, received $1.23 million for a project focused on improving two main categories of traits that affect the yield of high biomass energy sorghum: water use efficiency and drought resiliency. “You need a combination of those two traits in order to build an ideal energy crop for the U.S.,” Mullet says. “Water in a nonirrigated system is the primary limitation determining yield. That’s why this project focuses on improving the plant’s ability to use water to make biomass.”

Ceres has begun commercial development of sorghum. “There are well-established agronomic systems for sorghum, it’s high-yielding, grows quickly and fits well in with crop rotations, so it has received the most commercial interest to date,” Koppenjan says. “We have focused our efforts in Brazil where there is existing infrastructure and significant opportunities today for new energy crops to complement first generation feedstocks and increase bioenergy production.” 

Mullet says currently most of the sorghum being used for ethanol production in the U.S. is grain sorghum, but research estimates energy sorghum can produce twice as much biomass and biofuels when optimized. “We think it is a very promising commercial product, longer term,” Mullet says.

Another project selected to improve sorghum yield received $1.34 million. Patrick Brown, a quantitative geneticist at the University of Illinois, Urbana-Champaign, is working with a biochemist to characterize novel genetic variants that affect lignocellulosic composition and saccharification yield in bioenergy sorghum and closely related perennial grasses. “We are going to look at sorghum lines, and we are going to evaluate them for their agronomic performance,” Brown says. “Ultimately, what is really of interest is the economic yield per acre of different lines.”

Modified Miscanthus
The perennial miscanthus is being studied by Erik Sacks, at the University of Illinois, Urbana-Champaign, quantifying phenotypic and genetic diversity of miscanthus sacchariflorus. His project is receiving $1.5 million, and the goal is to develop molecular markers associated with traits of that can enable plant breeders to quickly develop improved biomass cultivars of miscanthus giganteus and closely related sugarcanes and energy canes.

Right now large-scale production is not commercially feasible for miscanthus because establishment costs are much higher than other energy crops, according to Koppenjan. “In miscanthus, we are developing seed-propagated varieties that have the same high-yielding attributes of current types of miscanthus, yet with establishment costs more comparable to other energy crops,” Koppenjan says.
Chemtex International Inc. is one company that plans to use the crop, among other energy grasses, as a feedstock at its 20 MMgy biorefinery in Clinton, North Carolina.

Strengthening Switchgrass
Switchgrass is another feedstock for cellulosic ethanol at Chemtex’s facility. Abengoa’s 25 MMgy biorefinery also plans to utilize switchgrass as a feedstock, among others. Research conducted by Robin Buell, a plant biologist at Michigan State University, East Lansing, received $1 million to identify traits associated with cold hardiness in switchgrass. One of the proposed mechanisms to increase switchgrass biomass is to grow lowland switchgrass cultivars in northern latitudes where they have higher yield potential, due in part, to their significantly later flowering time at these latitudes. Lowland switchgrass is not adapted to the colder winter conditions, however. Research has found that within the collective genetic diversity of the population, alleles, or alternative forms of the same genes, are present that confer cold tolerance. “If these alleles could be catalogued and converted into molecular markers, they would facilitate accelerated breeding and provide a mechanism to improve the efficiency of breeding switchgrass cultivars with high biomass and cold hardiness,” Buell says. This research has the potential to be applied in breeding programs for switchgrass that can thrive in northern climates.

Poplar Potential
Woody biomass also falls under the umbrella of energy crops with bioenergy production potential. Amy Brunner’s research at the Virginia Polytechnic Institute and State University received $1.43 million for a project that uncovers divergent and convergent regulatory networks that control growth responses to day length and nutrient stress in poplar. “The whole goal is to minimize water and nitrogen use, but maximize biomass production,” Brunner says. “We are really focusing on understanding how these two abiotic signals are perceived by poplar and, hopefully, identify different genes and networks, which could then be used in the future to improve the crop.”

Greenwood Resources Inc. is currently supplying ZeaChem Inc.’s 250,000 gallon-per-year cellulosic biorefinery with hybrid poplar trees from their farms within the vicinity of the plant in Boardman, Oregon.

Building a Portfolio
Researchers and developers seem to agree that building a portfolio of feedstocks is required for biofuel and biopower production. “What we want to see is really high-yielding and durable, sustainable varieties of these crops in multiple regions,” Ronning says.

Although current focus remains on improving and developing dedicated energy crops, potential for other feedstocks, like tropical grasses and even tobacco, are being considered for the future. “I think there are all sorts of opportunities, and as time goes forward there may be other crops that pop up here and there as potential biomass producers,” Jackson says.
Author: Katie Fletcher
Staff Writer, Ethanol Producer Magazine