Lignocelluloisc Biomass and Bioenergy

Lignocellulosic biomass is derived from trees and grasses and from agricultural residues and is one of the most abundant organic materials in the world. The value of this biomass as a energy source was first exploited over 700,000 years ago when early humans mastered the use of fire. Subsequently, humans have used biomass as building materials, as animal food, for clothing and for making paper.

The beginning of the 21 st century has seen increased interest in biomass for use in the large-scale production of liquid fuels. Biomass is a renewable, carbon-neutral energy that in combination with more efficient use of energy and increased energy conservation will allow us to reduce our dependency on ever-decreasing supplies of fossil fuel and to diminish the environmental costs of global warming.

In his 2006 State of the Union address, President George W. Bush introduced the Advanced Energy Initiative and stated that "For the sake of our economic and national security, we must reduce our dependence on foreign sources of energy – including on the natural gas that is a source of electricity for many American homes and the crude oil that supplies gasoline for our cars"

Subsequently, Samuel W. Bodman (The Secretary for Energy) introduced the Biofuel Joint Roadmap which set forth the goal of displacing 30% (60 billion gallons) of 2004 transportation fuel consumption with biofuels by 2030 and of making cellulosic ethanol a practical and cost-competitive alternative to gasoline by 2012.

To achieve these goals the US Dept of Energy has provided funds of $135 million over five years to each of three Bioenergy Centers. These centers will bring together multidisciplinary teams of scientists to advance research needed to make cellulosic ethanol and other biofuels commercially viable on a national scale.

In addition to geographic diversity, the three Centers are pursuing complementary scientific agendas:


• The DOE-ORNL Bioenergy Sciences Center (BESC) will focus on the resistance of plant fiber to breakdown into sugars and is studying the potential energy crops poplar and switchgrass.


• The DOE-UWM Great Lakes Bioenergy Research Center (GLBRC) is studying a range of plants and, in addition to exploring plant fiber breakdown, aims to increase plant production of starches and oils, which are more easily converted to fuels. This Center also has a major focus on sustainability, examining the environmental and socioeconomic implications of moving to a biofuels economy.


• The DOE-LBNL Joint Bioenergy Institute (JBEI) will concentrate on "model" crops of rice and Arabidopsis, in the search for game-changing breakthroughs in basic science, and is exploring microbial-based synthesis of fuels beyond ethanol.

 

 

The BESC Plant Cell Wall Polysaccharide Synthesis and Structure Group is located in the Complex Carbohydrate Research Center (CCRC) at The University of Georgia. Our mission is to:

                    Develop a thorough understanding of the genetics, biochemistry and cell biolgy of cell wall (biomass) biosynthesis

                    Understand how wall structure contributes to biomass recalcitrance

                    Use knowledge of wall synthesis and structure to guide generation of switchgrass and poplar plants with walls that are                     more readily converted to fermentable sugar

What is Lignocellulosic Biomass (a glossary of terms is provide here)

Lignocellulosic biomass is composed predominantly of the polysaccharide-rich primary and secondary walls that surround plant cells (see Figure 1). Most of the polysaccharides in biomass originate from the thick and strong secondary walls of the plant. Thus, biomass obtained from hardwoods (e.g. Populus - Populus trichocarpa) and grasses (e.g. switchgrass – Panicum virgatum) is composed predominantly of cellulose, hemicellulose, and lignin (see Table 1)

 

 

Converting Biomass to Biofuel

The production of ethanol from biomass involves numerous technologies (see Figure 2). Currently, most bioethanol is produced from cereal grains (e.g. corn [maize] starch) or from sugar cane.

 

 

Sugar cane cultivation requires a tropical or sub-tropical environment making this plant of limited value as a bioenergy crop in much of the continental US.

The use of corn for fuel production in the US has led to a worldwide increases in the price of corn-based foods and animal feeds, in large part because the US is the worlds major exporter of corn. In addition, corn is a high-maintainance crop that requires extensive use of water, fertilizer, and pesticides and thus is not a ideal bioenergy crop. The "fuel, food, or feed" debate raises numerous questions about food security that need to be addressed (UN Energy Biofuels).

Dedicated bioenergy crops (e.g. switchgrass and poplar), rather than food crops, are likely to become the major source of lignocellulosic biomass for large-scale production of liquid biofuels (Ragauskas et al. 2006). Bioenergy crops should give high-yields of biomass with low-maintainance costs, have little if any impact on food crop production, and be environmentally sustainable. Unfortunately, high processing costs currently make production of ethanol or other biofuels from lignocellulosic biomass too costly for broad impact, even at oil prices of $60-80/barrel.
A major barrier to reducing processing costs is the difficulty of enzymically releasing sugars from biomass for further use – this is the recalcitrance of biomass (Himmel et al. 2007). This recalcitrance is not unexpected as cell walls have evolved to be resistant to the action of hydrolytic enzymes to enable plants to survive in an environment where they are under constant threat from micro-organisms and animals.

Some of the structural features of lignocellulosic biomass that make it difficult to enzymically convert the polysaccharides to sugars are:

                    The crystalline nature of cellulose

                    The presence of hemicelluloses that coat cellulose fibers

                    The presence of lignin

                    The presence of waxes and phenolic compounds

                    The multi-layered architecture of cell walls

Harsh chemical treatments, which are costly, may alleviate some of these barriers. However, pretreating biomass may also increase recalcitrance by causing the polysaccharides and lignin to aggregate.

 

The Goal of the Bioenergy Science Center (BESC)

The overriding goal of BESC is to engineer wall biosynthetic pathways to generate plants with less recalcitrant walls that are deconstructed effectively by consolidated microbial bioprocessing. Technologies will be developed to achieve optimal sugar release and conversion from the biomass with minimal chemical pretreatment.

Research at BESC includes:

                    Biomass formation and modification (some of this research is described on this site - "Research Groups")

                    Poplar and switchgrass transformation technologies

                    Enzymic and microbial deconstruction of biomass

                    Development of superior biocatalysts for consolidated bioprocessing

                    Biomass characterization and modeling

Links to the plant transformation, biomass deconstruction, consolidated bioprocessing, biomass characterization, and biomass modeling research groups at BESC can be found on the "Internet Resources" Page