Biomass Conversion: 

Emerging Technologies, 

Feedstocks, and Products 

Research and Development 

Sustainability Program 

EPA/600/R-07/144 I December 2007 I www.epa.gov 
EPA/600/R-07/144 

December 2007 

Biomass Conversion:

Emerging Technologies, Feedstocks, and Products 

Sustainability Program 

Office of Research and Development

U.S. Environmental Protection Agency

Washington, D.C.
Credits and Notes

The principal researcher and writer for this report was Laura Kimes (lkimes@gmail.com), a former 

intern in the Sustainability Program of EPA’s Office of Research and Development through a 

cooperative arrangement with the Environmental Science and Policy program of the University of 

Maryland – College Park. Ms. Kimes joined the staff of the American Council on Renewable Energy 

in 2007. 

This project was initiated and directed by Donna Perla (perla.donna@epa.gov), Senior Advisor in 

ORD’s Sustainability Program and coordinator of EPA’s Waste-to-Energy Team. The project 

coordinator was Alan Hecht, ORD Director for Sustainability. Edward Fallon of ORD was the 

managing editor, Steve Wilson of ORD was the production coordinator, and Larry Gonzalez of EPA’s 

Office of Solid Waste was the technical advisor. 

This report has benefited from the comments and suggestions of EPA colleagues Rebecca Dodder and 

Andy Miller of ORD; Jaime Pagan, Brian Shrager, Bob Wayland and Kim Crossman, Rachel 

Goldstein, and Brian Guzzone of EPA’s Office of Air and Radiation. These individuals are not 

responsible for any remaining errors in this report. 

Cover photos (from left): Switchgrass plants in Oklahoma, 210 cm. in height; ethanol plant in York, 

Nebraska; and bus in Nebraska that runs on soybean biodiesel. All photographs are courtesy of the 

National Renewable Energy Laboratory Photographic Information Exchange (www.nrel.gov/data/pix/ 

searchpix.html). 

All Internet references in the report were current as of November 9, 2007. 

To download this report and 

learn more about EPA programs 

that support sustainability, please visit 

www.epa.gov/sustainability 

ii 
Table of Contents

Credits and Notes........................................................................................................................ii

Frequently Used Terms .............................................................................................................. iv 

Abstract and Introduction ........................................................................................................... 1

I. The Emerging Bioenergy Industry ......................................................................................... 3

The Role of EPA ................................................................................................................... 3

The Bioenergy Industry ........................................................................................................ 5

Biofuels................................................................................................................................. 5

Biobased Products................................................................................................................. 7

Biomass System.................................................................................................................... 8

The Biorefinery Concept....................................................................................................... 9

II. A Biomass Conversion Matrix ............................................................................................ 11

The Matrix .......................................................................................................................... 11

Eight Biomass Conversion Technologies ........................................................................... 11

Classifying Biomass Conversion Technologies.................................................................. 14

Feedstock and Pretreatment ................................................................................................ 21

Intermediate, Final, and Co-products.................................................................................. 22

Energy Conversion Processes ............................................................................................. 24

Appendix A. Selected Online Resources .................................................................................. 27

Appendix B. Ethanol Production Technologies........................................................................ 29

Appendix C. Biomass Conversion Matrix............................................................... 30 and Insert

iii 
Frequently Used Terms

Biobased Chemical Feedstock: an industrial chemical produced from biomass. 

Biobased Fuel (or “Biofuel”): any fuel used for transportation or other purposes produced from 

biomass.1 Biobased fuels are a type of bioenergy. 

Biobased Product (or “Bioproduct”): an industrial product produced from biomass, or a 

commercial or industrial product (including animal feed and electric power) derived through the 

process of converting biomass to fuel.2 

Biomass Energy (or “Bioenergy”): any useful, renewable energy produced from organic matter as 

complex carbohydrates in organic matter are converted to energy. Organic matter may be used 

directly as a fuel, may be processed into liquids and gases, or may be a residual of processing and 

conversion.3 

Biomass: any organic matter that is available on a renewable or recurring basis, including 

agricultural crops and trees, wood and wood wastes and residues, plants (including aquatic plants), 

grasses, residues, fibers, and animal, municipal, and other waste materials.4 

Biopower: electric power or heat derived from direct combustion of biomass feedstock through 

gasification and then combustion of the resultant gas or through other thermal conversion processes. 

Power is generated with engines, turbines, fuel cells, or other equipment.5 Biopower is a type of 

bioenergy. 

Biorefinery: a facility that processes and converts biomass into value-added products, which can 

range from biomaterials to fuels such as ethanol or important feedstocks for producing chemicals and 

other materials. Biorefineries can be based on several processing platforms using mechanical, thermal, chemical, and biochemical processes.6 

Feedstock: a material that is converted to another form or product.7 

1 Biomass Research and Development Act, Revised by the Energy Policy Act of 2005, Sec. 303. [7 U.S.C. 7624 note] 

Definitions, <http://www.brdisolutions.com/initiative/hidden%20pages/1/Developmentaspx>. 

2 Ibid. 

3 “Bioenergy Feedstock Information Network” (BFIN), <http://bioenergy.ornl.gov>.

4 Biomass Research and Development Act, op. cit..

5 “Bioenergy Feedstock Information Network” (BFIN), <http://bioenergy.ornl.gov>.

6 Ibid. 

7 Iowa State University, Office of Renewable Programs, “Glossary of Biorenewable Terms,” 

<http://www.biorenew.iastate.edu/resources/glossary-of-biorenewables-terms.html>. 

iv 
Abstract

The Biotechnology Matrix and the Biomass System 

The centerpiece of this report is a comprehensive matrix (in Appendix C and as an insert in 

larger format) that presents eight technologies now being developed to convert biomass 

feed stocks to energy. The matrix displays the biomass system from feedstock through 

conversion to sugars and other intermediate products, to fuel and energy, and to final 

products. A variety of products may be created from a given feedstock; similarly, a particular 

final product may be derived from different feedstocks and conversion technologies. The 

matrix shows that different energy sources are driving the technologies that convert plant 

matter into fuel and energy. 

This report describes the principal steps in the biomass system: (1) growing and harvesting 

(or collecting), (2) processing into feedstock, (3) conversion into sugar and other 

intermediate products, (4) conversion into energy and other final products, (5) distribution of 

these products, and (6) their use as biofuels, power, and other biobased products. The 

technical and economic viability of this complex system relies on a reliable feedstock supply, 

efficient conversion technologies and distribution systems, and effective demand and 

markets for the byproducts and final energy products. 

Introduction

Human Labor, Fossil Energy, Biomass 

For millennia humans have supplemented their own labor with energy from draft animals, sun and 

wind, and burning wood and whale oil – ancient sources of bioenergy. Fossil fuels have supplied 

energy for specialized purposes for many centuries, but the industrial revolution greatly expanded 

their extraction and use. Fossil fuels have provided immense quantities of inexpensive and highdensity energy, they are finite in quantity, are often buried in inconvenient locations, and release 

large amounts of carbon dioxide into the atmosphere. In recent years, rising petroleum prices linked 

to higher drilling costs and an inevitable decline of production – as well as concerns for the environment, rural prosperity, and national security – have heightened interest in biomass (renewable organic 

matter) as a source of fuel and other forms of energy. 

Using biological material for transportation fuel is not new. Seeking a viable alternative to the coalfired steam engine, Rudolph Diesel used peanut oil in his compression engine in 1898. Vegetable oils 

were used in diesel engines until the 1920s, when alterations enabled the engines to use a residue 

of petroleum – what we now call “No. 2 Diesel.” Beginning with the 1908 Model T, Henry Ford 

designed his automobiles to use ethanol. Convinced that renewable resources were crucial for the 

success of his business, Ford built an ethanol refinery in Kansas and formed a partnership to sell the 

biofuel in Standard Oil stations; 25-percent-ethanol fuel became widely used in the Midwest. Despite 

1 
Ford’s continued promotion of ethanol, biofuels were replaced in the 1940s by lower-priced, 

aggressively marketed petroleum products. 

The Corn Ethanol Boom 

From providing just one percent U.S. of the nation’s transportation fuel supply in 2000, ethanol 

production roughly quadrupled by 2007 to an expected 7 million tons, about 3 percent of the nation’s 

vehicle fuels. Ethanol production is likely to soar in the next several years as refineries now under 

construction or expanding will nearly double current capacity. The Department of Energy expects 

ethanol to greatly exceed the goal of 7.5 billion gallons of annual domestic renewable fuel 

production by 2012 set by the 2005 Energy Policy Act. Nearly all of this will be from corn ethanol, 

which now uses about 18 percent of U.S. corn production. President Bush has set a goal that 

cellulosic ethanol – refined from the woody plant matter in the rigid cell wall material that makes up 

the greater part of plants – will be cost-competitive with corn ethanol by 2012. With the further 

development of cellulosic conversion technologies like those described in this report, the White 

House goal of producing 35 billion gallons a year of ethanol by 2017 could be attained with less 

reliance on corn ethanol. 

The Promise and Challenge of Cellulosic Biomass 

Cellulosic ethanol differs from corn- and other grain-based ethanol in that it may be distilled from the 

fermentation of sugars from the entire plant, not just from the grains. Cellulosic biomass feedstocks 

include agricultural plant wastes (corn stover, cereal straws, and sugarcane bagasse), wastes from 

industrial processes (sawdust and paper pulp) and municipal waste (grass clippings, table scraps), 

and crops grown expressly for fuel production (switchgrass, sugarcane, and fast-growing trees like 

poplar and willow). The sugars in cellulose are locked in complex carbohydrates (consisting of long 

chains of simple sugars) that are generally more recalcitrant to the action of enzymes to separate these 

complex structures into fermentable sugars. Some of the new and emerging technologies for breaking 

down forms of cellulosic biomass to sugars for energy production described in this report will likely 

become key drivers in diversifying ethanol production to meet the wide expectation that cellulosic 

material will become the dominant ethanol feedstock in coming decades. 

2 
I. The Emerging Bioenergy Industry 

Since the first major federal funding for renewable biomass-derived energy began in the 1970s,8 the 

bioenergy industry has shown economic and technological advances, and political support for the 

industry continues to grow. This growth is especially notable in more recent years because of a timely 

convergence of policy, legislation, technology, and investment interest, which has ensured that the 

industry will be a major consideration in energy and agricultural policies. The National Energy Act 

(2005) provided guidance for promoting biomass-derived energy. The President’s 2006 Advanced 

Energy Initiative called for improved and alternative 1) transportation fuel, and 2) domestic and 

workplace power sources;9 both recommendations feature bioenergy prominently. The President’s 

“Twenty in Ten” energy goal called in 2007 for reducing U.S. gasoline consumption by 20 percent by 

2017.10 Steps toward achieving this goal include (1) increasing the supply of renewable and 

alternative fuels through a mandatory fuels standard requiring use of 35 billion gallons of renewable 

and alternative fuels in 2017 and (2) reforming and modernizing corporate average fuel economy 

(CAFE) standards for cars and light trucks. 

The Role of EPA 

The 2005 National Energy Act charged the EPA with helping to support diverse research and 

development as well as the purposes and objectives of the Biomass Act of 2000. The goals and 

objectives include these: 

• Developing technologies for abundant production of competitively priced biobased fuels 

• Developing biobased products 

• Developing a diverse and sustainable domestic supply of biomass feedstock 

• Increasing energy security 

• Increasing rural development 

• Enhancing environmental and public health, and 

• Diversifying markets for raw agricultural and forestry products 

Since the passage of these acts, the Office of Research and Development (ORD) has focused on 

applying sustainability principles to the biomass system, as well as pursuing research and 

development in areas relevant to the biomass system. EPA’s Office of Air and Radiation (OAR) has 

8 Helena Chum, “Biofuels in the Energy Mix,” slide presentation at “The Promise of Energy Independence: Examining 

National Policy and Regional Action Forum” (University of Maine, October 5, 2005), 

<http://www.library.umaine.edu/cohen/forum/chum.pdf>. 

9 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, “Biomass FAQs,” 

<http://www1.eere.energy.gov/biomass/biomass_basics_faqs.html>.

10 The White House, “Energy Security for the 21st Century,” <http://www.whitehouse.gov/infocus/energy>.

3 
4 4

significant responsibilities under the Clean Air Act related to clean fuels, as well as responsibilities 

under the Energy Policy Act related to renewable fuel standards. Several voluntary OAR programs 

aim at achieving clean air and reducing greenhouse gas. EPA’s Region 7 (Nebraska, Kansas, Iowa, 

and Missouri) has significant interest in ensuring sustainable biomass production and agricultural 

practices and biomass production. Region 7 and other EPA Regions are also interested in shifts in 

land use and other environmental impacts from agricultural practices and biofuel facilities. 

Significant research is needed to ensure sustainable biomass production, including research to 

quantify any potential effluents, emissions, wastes, and net energy use from current and future 

biomass conversion systems, along with energy and water efficiencies. The impacts of integrated 

options for feedstock, technology, and distribution on land, water, and energy use ought to be 

considered in order to sustain the value of long-term investments in certain geographic regions. 

Differences among EPA regions will help advance understanding of biomass conversion systems. 

Because of geographic variations among biomass systems, some regions are more “biomass-rich” 

in particular categories of biomass, as illustrated by Region 7’s abundance of agricultural crops 

suitable for biofuels. Figure 1 depicts the total national biomass resources available per square 

kilometer by county in each EPA region. This total biomass estimate includes crop residues; methane 

emissions from manure management, landfills, and wastewater treatment facilities; forest residues; 

primary and secondary mill residues; urban wood waste; and dedicated energy crops.11 All EPA 

regions, however, have biomass conversion potential that should be understood. 

One way of furthering balanced biomass development is to ensure that policymakers, permit writers, 

and loan grant program directors understand the diverse options of biomass conversion technologies. 

This report gives context and information about many bioenergy technologies with a particular focus 

on emerging technologies that are not presently common in commercial applications. It does not 

Annual 

Tons 

Biomass 

(per sq. km.) 

0 - 56 

57 - 135 

136 - 234 

235 - 365 

366 - 533 

534 - 790 

791 - 1467 

1468 - 3415 

3416 - 6225 

Figure 1. Total Biomass Density in the Continental U.S. 

(Data: National Renewable Energy. http://www.nrel.gov/gis/data_analysis.html) 

11 National Renewable Energy Laboratory, “Dynamic Maps, GIS Data, and Analysis Tools,” 

<http://www.nrel.gov/gis/data_analysis.html>. 
55 

cover, for example, the combustion technologies are already playing a large role in the production of 

biomass power, heat, and combined heat and power (CHP). 

The Bioenergy Industry 

Political, economic, and technologic circumstances have reshaped the bioenergy industry as a 

significant contributor to national renewable energy in recent years. Since 2003, energy from biomass 

has been the leading source of renewable energy production by source in the United States,12 and 3 

percent of the nation’s total energy consumption is derived from biomass.13 Furthermore, biomass 

use in the industrial sector is expected to increase at a rate of 2 percent annually in the industrial 

sector and to double every ten years in the electric utility sector.

14 

Collaboration among federal agencies has supported the recent momentum contributing to this 

increased interest in bioenergy. The Biomass Research and Development Act of 2000 charged federal 

agencies with the task of coordinating and accelerating “all Federal biobased products and 

bioenergy research and development.”15 This Act created the Biomass Research and Development 

Board (BRDB), with representation from the Environmental Protection Agency, the Departments of 

Agriculture, Energy, Interior, and Transportation, National Science Foundation, Office of Science and 

Technology Policy, and the Office of the Federal Environmental Executive.16 

Biofuels 

The bioenergy industry has gained momentum in recent years due in part to focused funding and 

research for ethanol production. Current commercialized technologies for ethanol production are 

limited in using feedstocks from grains and other carbohydrates. Still, ethanol production in recent 

decades has increased since the 1980s (Figure 2). 

Efforts by groups such as the President’s Advanced 

Energy Initiative, the Biomass Research and 

Development Board, DOE, USDA and the EPA are 

accelerating research, development, and 

commercialization of cellulosic ethanol. Proponents 

of cellulosic ethanol suggest that it will have many 

benefits over carbohydrate-based ethanol 

production, including many environmental and 

economic advantages. (See Appendix B.) Scientists 

have suggested that further research can make 

cellulosic ethanol cost-competitive by 2012, offering 

the potential to displace up to 30 percent of current 

U.S. fuel use.17

 12 U.S. Dept. of Energy, Energy Information Agency, Monthly Energy Review, Table 1.2 Energy Production by Source 

(March 2007), <http://www.eia.doe.gov/emeu/mer/pdf/pages/sec1_5.pdf>. 

13 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, “Information Resources 

for Consumers,” <http://www1.eere.energy.gov/biomass/for_consumers.html>. 

14 U.S. Depts. of Agriculture and Energy, “Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The 

Technical Feasibility of a Billion-Ton Annual Supply,” (2006), 

<http://feedstockreview.ornl.gov/pdf/billion_ton_vision.pdf>.

15 Biomass Research and Development Initiative <http://www.brdisolutions.com >. 

16 Ibid. 

17 The White House, “State of the Union: Advanced Energy Initiative” (January 31, 2006), <http://www.whitehouse.gov/ 

news/releases/2006/01/20060131-6.html>. 

Figure 2. Historic National Ethanol Production 

(Data: Renewable Fuel Association) 
Within the U.S., much of the biofuel emphasis is poised to shift to cellulosic ethanol. Replacing 30 

percent of the fuel supply with biofuels will necessitate a dramatic increase of biomass availability. 

Besides higher yields of grains and seeds, conversion of cellulosic biomass from such non-food 

sources as fibrous, woody, and inedible portions of plant matter will be required, likely leading to 

cellulosic biomass eventually replacing corn-based ethanol. Cellulosic feedstocks will use 

feedstocks such as crop residues, woody biomass, and switchgrass. Driving this shift is the President’s 

commitment to making cellulosic ethanol cost-competitive with corn-based ethanol by 2012. 

This transition will call for large supplies of sustainable feedstock, major feedstock and conversion 

technology advances, large-scale integrated bio-refinery demonstrations, and massive new 

infrastructure development that will affect land use and ecosystems. Policy and market-based 

incentives and extensive permitting of new facilities will be needed to facilitate this transition, which 

is expected to cover the next 25 years. Current corn-based biofuels will dominate commercial use at 

least until 2012 when the first commercial cellulosic biofuels plants are likely to become 

operational.18 

There are many types of biofuels. Though ethanol is today by far the dominant biofuel in production 

in the U.S., many different types of biofuels are available including biodiesel, methanol, biocrude, 

and methane.19 A variety of national policies and goals are supporting all biofuels, not just ethanol. 

In 2001, just 0.5 percent of total U.S. transportation fuels consumed were biofuels.20 However, in 

support of the President’s Advanced Energy Initiative, the Department of Energy’s National Biofuels 

Initiative has set a goal that biofuels will provide by 2030 an amount equal to 30 percent of today’s 

U.S. gasoline consumption.21 In fact, U.S. biodiesel production has greatly increased in recent years 

(Figure 3). As discussed above, ethanol production also has a large national significance. 

Biofuel production has a global significance. From 

2004 to 2005, the total million gallons of ethanol 

produced worldwide increased by 13 percent, from 10,770 

to 12,150 million gallons.22 Interest in and production of 

biodiesel production has also increased worldwide. From 

2000 to 2005, global biodiesel production has increased 

fourfold, due in part to huge interest in the EU, where 

biodiesel accounts for 80 percent of the region’s total 

biofuels production.23 In March 2007, the United States 

Figure 3. Estimated U.S. Biodiesel Sales and Brazil signed a memorandum of understanding to 

(Data: National Biodiesel Board) advance cooperation on biofuels”, both biodiesel and 

18 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, “Biofuels Initiative,” 

<http://www1.eere.energy.gov/biomass/biofuels_initiative.html>. 

19 U.S. Dept. of Energy, National Renewable Energy Laboratory, “Biofuels for Sustainable Transportation” (June 2000), 

<http://www.nrel.gov/docs/fy00osti/25876.pdf>. 

20 Oak Ridge National Laboratory, “Growth in Biomass Could Put U.S. on Road to Energy Independence” (April 21, 

2005), <http://www.ornl.gov/info/press_releases/get_press_release.cfm?ReleaseNumber=mr20050421-01>. 

21 U.S. Dept. of Energy, National Renewable Energy Laboratory, “Biofuels for Sustainable Transportation” (June 2000), 

<http://www.nrel.gov/docs/fy00osti/25876.pdf>. 

22 Renewable Fuels Association, “Industry Statistics,” <http://www.ethanolrfa.org/industry/statistics>. 

23 World Watch Institute, “Biofuels for Transportation: Selected Trends and Facts” (June 7, 2006), 

http://www.worldwatch.org/node/4081>. 

6 
7 

ethanol.24 Although Brazil is recognized for its leadership in ethanol production, other countries have 

also significantly increased their biofuel production; Germany, for example, raised its biodiesel production fivefold from 1995 to 2001.25 

Various crops are grown worldwide for both food and energy uses--corn and soybean in the U.S., 

flaxseed and rapeseed in Europe, sugar cane in Brazil and palm oil in Southeast Asia. Corn and 

sugarcane are the predominant feedstocks used to produce ethanol fuels worldwide, while soybeans 

and rapeseed oils are used to produce biodiesel. The dual use as both food and energy for many of 

these crops has led to rising market prices for many goods. Most recently, corn prices in the U.S. have 

risen in response to ethanol-related demand for the crop.26 

Biomass Conversion Uses Three Types of Technology. Three basic categories of technologies can 

convert biomass into inert gases and organic oils, gases, and fuels that can be further used to yield 

desired energy products. 

• Thermochemical technologies use high temperatures to convert biomass feedstocks to energy, 

typically in the form of electricity and heat. However, the technologies have the potential to 

produce electricity, heat, bioproducts, and fuels. 

• Biochemical technologies use biological agents to convert biomass feedstocks to energy, 

typically in the form of liquid and gaseous fuels. However, the technologies have the potential to 

produce electricity, heat, bioproducts, and fuels. 

• Chemical technologies use chemical agents to convert biomass feedstocks to energy, typically in 

the form of liquid fuels. 

These three biomass conversion technologies are not limited to producing only bioenergy: they may 

also produce byproducts that, if efficiently managed, can be valuable biobased products. 

Biobased Products 

Biomass can be converted into products such as chemicals, polymers, animal feed, and construction 

material, rendering lower-value biomass materials and waste products into higher value products. 

These biobased products are created from low-value biomass feedstocks, which are often waste 

products from bioenergy production. Biobased chemical products can be a particularly profitable 

sector in biobased products. Biobased chemical products are valued as some of the most common and 

essential chemical feedstocks required in chemical manufacturing. As biomass conversion becomes 

increasingly popular and the necessary linkages between bioenergy production and bioproduct 

production are formed, this sector has the potential to grow rapidly. 

24 U.S. Dept. of State, Office of the Spokesman, Fact Sheet, “Advancing Cooperation with Brazil on Biofuels” (March 9, 

2007), <http://www.state.gov/r/pa/prs/ps/2007/mar/81589.htm>. 

25 U.S. Dept. of Agriculture, Foreign Agricultural Service GAIN Report, “Germany, Oilseeds and Products, Biodiesel in 

Germany – An Overview” (October 24, 2002), <http://www.fas.usda.gov/gainfiles/200210/145784397.pdf>. 

26 U.S. Dept. of Agriculture, Foreign Agricultural Service Circular Series, “Grain: World Markets and Trade, 

Tightening 2006/7 Global Grain Supplies to Boost Prices” (May 2006), <http://www.fas.usda.gov/grain/ 

circular/2006/05-06/graintoc.htm>. 
6. Consumer 5. Distribution 

4. Energy Production 

Figure 4. The System of Biomass as an Energy Source 

The Biomass System 

Biomass as an energy source is a system of interdependent components. Economic and 

technical viability of this system relies on a guaranteed feedstock supply, effective and efficient 

conversion technologies, guaranteed markets for the energy products, and cost-effective distribution 

systems. (1) The system begins with biomass harvesting (or biomass collection of non-agricultural 

waste); (2) this biomass is then prepared as feedstock, (3) which is converted to intermediate 

products. (4) These intermediate products are converted to final energy and other biobased products; 

(5) which are finally distributed and (6) used for biofuels, biopower, and biobased products. This 

system is illustrated in Figure 4 and detailed further in the following paragraphs. 

1. Harvest 2. Feedstock 3. Conversion 

Biomass can be harvested or collected for use as energy (Figure 4.1). Agricultural biomass is 

harvested and can be used for food and energy, while waste biomass is collected but can be used 

solely for energy. The synapses between food and energy create special concerns for agricultural 

biomass. Agricultural crop and forestry systems depend on the inputs of water, nutrients, and seed so 

that grain and crop residues can be produced. Typically, crop and forestry system products are used 

for the production of food and lumber, and the subsequent development, harvesting, and dispersal 

may present environmental challenges. Agricultural energy systems extend this traditional system, 

and some potential environmental issues are subsequently heightened. Such changes that may 

accompany this increased production include depletion of water supply and declines in water and soil 

quality, as well as increases in pesticide concentrations, migration of plantings of genetically 

modified organisms (GMO), and nutrient overloads. 

8 
Feedstocks can be derived from agricultural, forest, or waste products (Figure 4.2). Biomass can 

come in almost any form. Typical feedstocks include forest residues, agricultural crops and residues, 

wood and wood residues, aquatic plants, and fast-growing trees and plants. Typical waste feedstocks 

include municipal solid waste, construction waste, agricultural waste, animal manure, meatpacking 

waste, food processing waste, spent pulping liquor, cooking oil, paper mill residue, and wastewater 

treatment sludge. The process through which the biomass is converted to energy is dependent on the 

chemical composition, homogeneity, size, amount, and water content of the feedstock. Also, 

geographic location is a consideration, as biomass must be transported from farm to biorefinery. (See 

the Feedstocks column in Appendix C. Biomass Conversion Matrix.) 

Technologies convert feedstock to intermediate products (Figure 4.3). Conversion processes, 

which include several technologies that decompose biomass into intermediate products, also come in 

many different forms and configurations. Depending on the feedstock, different methods are needed 

for conversion into intermediate products. A given feedstock may be appropriate for several different 

conversion pathways into intermediate products. Conversion technologies may be classified at several 

levels. At the highest level, feedstock decomposition processes are carried out principally through 

biochemical, thermochemical, or chemical means. The classification is quite specific and is based on 

engineering specifications, such as bed placement in a gasifier. Pre-processing techniques can also be 

used to prepare a feedstock for more efficient conversion. (See Column 1 in Appendix C.) 

Intermediate products are converted to final products (Figure 4.4). A primary intermediate 

product results from each of the feedstock conversion processes. These products are of four 

principal types: an inert gas, a combustible gas, an oil/tar, and a combustible fuel. Further 

processing of intermediate products can produce end products, such as electricity, heat, fuels, and 

chemicals. Many options for converting an intermediate product to high-value end product are 

commercially available. Such options include: turbines, combustion, distillation, and Fischer-Tropsch 

catalytic conversion processes. (See Column 3 in Appendix C.) 

Final products may face distribution issues (Figure 4.5). Final products such as transportation fuels, electric power, heat, and chemicals often face distribution problems. A closed biorefinery system 

uses the final products within the facility that supplied the feedstock, such as a cattle farm powered 

by an anaerobic digester-combustion facility. For an open biorefinery system, by contract, distribution 

issues must be considered and resolved: for example, the need to meet state and federal regulations 

for distributed energy in order to resell bioenergy to the grid.27 In the case of corn-derived biofuel, 

fuels must be transported, sometimes at great distances, from ethanol production plants to gasoline 

blending facilities. Some material incompatibilities are associated with product distribution; for 

example, ethanol can be corrosive to such major infrastructure as storage tanks and pipelines. 

Products are delivered to energy consumers (Figure 4.6). In the final step of the biomass to energy 

process, consumers receive biofuel, biopower, and bioproducts. 

The Biorefinery Concept 

Biorefineries can integrate preprocessing, conversion, and production processes within a single 

facility. Like petroleum refineries which process crude petroleum into higher-value products, a 

27 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy Distributed Energy Program, “Deployment: 

Grid Interconnection,” <http://www.eere.energy.gov/de/grid_interconnection.html> 

9 
10 

biorefinery is a facility which converts biomass to higher-value products such as electricity, fuels, 

heat, and chemicals. The biorefinery concept of the National Renewable Energy Laboratory (NREL) 

builds on two distinct “platforms” that promote distinct groups of products. The sugar platform uses 

biochemical conversion and focuses on fermenting sugars extracted from biomass feedstocks. The 

syngas platform uses thermochemical conversion and focuses on gasification of biomass feedstocks 

and byproducts from conversion processes.28 

NREL and many other government agencies consider the biorefinery as a viable option through 

which national security concerns, energy supplies, rural development, sustainability, and conservation 

efforts may all be addressed. This biorefinery scheme allows for both input and output flexibility 

according to feedstock supplies and market demands. 

28 National Renewable Energy Laboratory, “Biomass Research: What Is a Biorefinery?” 

<http://www.nrel.gov/biomass/biorefinery.html> 
11 

II. A Biomass Conversion Matrix 

The Matrix 

This section describes and explains the Biomass Conversion Matrix in Appendix C, providing a 

framework for understanding the potential for different biomass conversion technologies within a 

more comprehensive biorefinery infrastructure. 

This matrix displays, through stages of their specific energy-conversion processes, many of the most 

promising among the wide assortment of bioconversion technologies that are not now widely used 

in commercial applications. Portions if the matrix are presented in the text and the entire matrix is 

presented in large format in Appendix C – which serves as a map to simultaneously display important 

features of the previously discussed system of using biomass as an energy source. The matrix 

displays the system from feedstock through conversion technology, intermediate product, and 

product-to-energy conversion method, to energy product. Each feedstock may be used to create a 

large variety of products, and likewise, a single product may be derived from many different 

feedstocks and conversion technologies. Thus, it is important to understand the matrix as a system. 

The matrix is reproduced in a smaller format in Figure 5, which shows the major matrix features. It is 

a two-dimension table, with one axis corresponding to levels and sub-levels of conversion technology 

classification. The other axis specifies the feedstock, intermediate products, product-to-energy 

conversion method, and energy products of each conversion technology. 

Eight Biomass Conversion Technologies 

The eight conversion technologies examined in this report have been selected because of their 

relatively advanced state of development and expected future contribution to bioenergy. These 

emerging technologies all have solid promise, with some already well established. (This list omits 

combustion technologies such as stoker boilers and fluidized bed boilers that are already widely used 

in commercial applications.29) 

Gasification is a thermochemical decomposition process through which biomass or other organic 

matter is converted to a gaseous state in the limited presence of oxygen.30 

29 For detailed technical information on commercial conversion technologies for biomass power and hear, see U.S.EPA, 

Combined Heat and Power (CHP) Program, “Catalog of CHP Technologies” (2007) 

<http://www.epa.gov/chp/basic/catalog.html>. 

30 U.S. Dept of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Technologies, “Biomass 

Gasification” <http://www1.eere.energy.gov/biomass/gasification.html>. 
1. Biomass Conversion 

Technology 2. Feedstocks 3. Products 

Downdraft Co-Current Fixed Bed 

Updraft Co-Current Fixed Bed 

Cross-Draft Fixed Bed 

Open Core Fixed Bed 

Pressurized Circulating Fluidized Bed 

Atmospheric Circulating Fluidized Bed 

Plasma Arc Gasifier 

2-stage Gasifier 

Open Top 

Aqueous Phase Reforming 

Ablative Fast Pyrolysis 

Cyclonic Fast Pyrolysis 

Rotating Core Fast Pyrolysis 

Open Core Fast Pyrolysis 

Vacuum Pyrolysis 

Flash Pyrolysis 

Any Organic Material 

Examples: Agricultural wastes, hazardous organic wastes, 

industrial wastes. 

Pretreatment: Waste typically segregated. 

Qualifications: Dry MSW is favorable. Coal size distribution must 

be controlled to ensure good bed permeability. 

Final Conversion Technology (Optional): Fischer-Tropsch 

Catalytic Conversion 

Any Organic Material 

Pretreatment: Sorting 

Qualifications: None 

Any Organic Material 

Pretreatment: Sorting. 

Qualifications: Waste must be pre-sorted and processed to 

<6 mm (1 to 2 mm. preferred) and <10% moisture content to 

assure high heat transfer rate. 

Intermediate products: Syngas and Charcoal 

Final Products: Bio-Oil and Charcoal 

Co-products: Electricity and Thermal Energy 

Grains 

Mostly: Corn 

Pretreatment: Separation of the oil, protein, fiber and the bulk of 

the nutrients from the starch 

Grains, Sugars and Waste , Starches and Sugars 

Examples: Grains (corn, sorghum, barley), Sugars (Sugarcane and 

beets), Beer, and other waste sugars and starches. 

Pretreatment: Grinding, cooking and fermentation 

Cellulosic/Woody Biomass 

Pretreatment: Hydrolysis (Dilute Acid, Concentrated Acid, 

Enzymatic, Steam explosion) 

Wet-Mill Fermentation 

Dry-Mill Fermentation 

Lignocellulosic Biomass Fermentation 

Thermochemical Biochemical Chemical 

Gasification Pyrolysis Ethanol Production Anaerobic Digesters Landfill Aerobic Biodiesel Production 

Mesophilic Process or Thermophilic

Process 

Slow

Pyrolysis 

Fast

Pyrolysis 

Novel

Design 

Fluidized

Bed 

Fixed

Bed 

Anaerobic activated sludge process 

Anaerobic clarigester 

Anaerobic contact process 

Anaerobic expanded-bed reactor 

Anaerobic filter 

Anaerobic fluidized bed 

Anaerobic lagoon 

Anaerobic migrating blanket reactor 

Batch system anaerobic digester 

Expanded granular sludge bed digestion 

Hybrid reactor 

Imhoff tank 

One-stage anaerobic digester 

Submerged media anaerobic reactor 

Two-stage anaerobic digester 

Upflow anaerobic sludge blanket digestion 

Upflow and down-flow anaerobic attached 

growth 

Bioreactor vessel 

Landfill Site 

Static Pile 

Enclosed Compost 

Turned Window 

In-Vessel Compost 

Transesterification 

Practically any Organic Waste 

Pretreatment: Sorting 

Qualifications: A separation between organic and contaminants is 

necessary. 

Oils, fats, used cooking oils, greases, methanol or ethanol and 

a catalyst 

Pretreatment: Used cooking oils, yellow greases, and some tree 

oils are taken through an esterification process to remove fatty acid 

that should, preferably, be reduced to less than 1% (at least below 

4%). 

Qualifications: Essentially any bio-oil, animal fat or tallow, used 

cooking oil, yellow/trap grease, plant or tree oil can be converted 

into biodiesel if the fatty acid content is low enough. 

Organic Wastes 

Pretreatment: Sorting pre-treatment 

Qualifications: The waste must be contained, compacted and 

covered in a vessel 

Organic Wastes 

Pretreatment: None Qualifications: None 

Intermediate products: None 

Final Products: Valuable Compost 

Co-products: Heat and Carbon Dioxide. (May be useful in a 

greenhouse environment or for heating) 

Intermediate products: N/A. 

Final Products: Biogas, Thermal Energy, Digestate. 

Co-products: Liquid and Solid Biofertilizers. 

. 

Almost any organic material: paper, grass clippings, leftover food, 

sewages, animal wastes; and other forms of biomass such as 

distillers grains. 

Pretreatment: Sorting or screening to remove inorganic material. 

Qualifications: The material may need to be pre-processed and 

water added. 

. 

. 

Conversion technologies platforms 

are classified according to 

decomposition process, and 

engineering specifications. 

Appropriate 

feedstocks 

correspond to each 

conversion technology. 

Resulting products 

correspond to each 

conversion 

technology. 

Intermediate Products: Combustible gases, liquids, tars, and 


inert fluidizing gases.


Final Products: Electricity, Thermal Energy, Hydrogen, Ethanol 


and other alcohols, Diesel type fuels, Gasoline.


Co-products: Charcoal, Ash, Carbon Dioxide.


Intermediate Products: Mash, Sugar 

Final Products: Ethanol 

Co-products: Distillers grains plus solubles, Carbon Dioxide 

Intermediate Products: Starch, Sugar 

Final Products: Ethanol 

Co-products: Corn oil, corn gluten meal, corn gluten feed, carbon 

dioxide, liquid bio-fertilizers 

Intermediate Products: Cellulose, hemicellulose. lignin


Final Products: Ethanol


Co-products: Carbon Dioxide, residual cellulose and lignin,


electricity and thermal energy


Intermediate products: Biogas composed of Methane, Carbon 


Dioxide, Nitrogen, Hydrogen, Hydrogen Sulfide and Oxygen.


Final Products: Electricity, thermal energy, methane. CNG or LNG 


for vehicle fuel.


Co-products: Carbon Dioxide for possible use in greenhouse 

operations, and Biofertilizers. 

Intermediate Products: Oils fats or greases taken through 

transesterfication 

Final Products: Biodiesel 

Co-products: Glycerin, Soaps 

12 

Figure 5. Biomass Conversion Matrix 

(See Appendix C. for enlargement of this matrix.) 
13 

Pyrolysis (as used in this report) is a thermochemical decomposition process through which biomass 

or other organic matter is converted to a mixture of oil, gases, and carbon residues in the complete 

absence of oxygen.31 

Starch and sugar fermentation is a direct biochemical decomposition process through which 

glucose-containing material is chemically decomposed in the presence of oxygen using enzymes to 

form ethanol and carbon dioxide32. The method requires no or minimal preprocessing. 

Lignocellulosic biomass fermentation is a biochemical decomposition process through which 

biomass containing lignin, cellulose, and/or hemicellulose is pretreated to break into component 

sugars, and then is chemically decomposed to form ethanol and carbon dioxide33. The method 

includes the use of a saccharification step, in which calcitrous feedstock is preprocessed into 

fermentable sugars. Once preprocessed, this type of biomass is fermented as in “3, Starch and Sugar 

Fermentation” in preceding paragraph. (Appendix A illustrates how the process of starch and sugar 

fermentation differs from lignocellulosic biomass fermentation.). 

Transesterification is a chemical reaction through which alcohol groups from an alcohol catalyst 

bond to fatty acids from oils, fats, and greases. This process both reduces the viscosity of the fatty 

acids and converts them to a combustible form. Esterification is a pretreatment process sometimes 

necessary to prepare the fatty acids for transesterification.34 

Anaerobic digestion is a biochemical process through which biomass or other organic matter is 

consumed by bacteria and subsequently released in a gaseous state. This process occurs in the 

absence of oxygen.35 Different types of bacteria can be used for this process: psychrophilic, 

mesophilic or thermophilic processes, depending on bacterial affinity for cool, intermediate or warm 

temperatures, respectively. 

Landfill gas collection is a process through which gaseous effluent is collected from decomposing 

organic material at a waste disposal site. The waste decomposes under naturally anaerobic or 

manipulated aerobic conditions, and produces primarily methane and carbon dioxide. Gas is then 

collected from landfills.36 

31 U.S. Dept of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Technologies, “Pyrolysis 

and Other Thermal Processing” <http://www1.eere.energy.gov/biomass/pyrolysis.html>. Some technical literature 

refers to the first step in biomass gasification as “pyrolysis,” but this is not the same process as the pyrolization of 

biomass discussed in this report. See Anthony V. Bridgwater, “Biomass Fast Pyrolysis,” Thermal Science 8 (2004), 

21-49, <http://thermalscience.vin.bg.ac.yu/pdfs/2004-2/TS22004Cl2.pdf>.

32 State of Oregon, Biomass Energy Home Page, “Biofuels Technologies,” 

<http://www.oregon.gov/ENERGY/RENEW/Biomass/biofuels.shtml>. 

33 Ibid. 

34 U.S. Dept of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Other Platforms (2006), 

<http://www1.eere.energy.gov/biomass/other_platforms.html>; National Biodiesel Board, “Biodiesel Production,” 

<http://www.biodiesel.org/pdf_files/fuelfactsheets/production.pdf>., Hideki Fukuda et al, “Biodiesel Fuel Production 

from Transesterification of Oils,” Journal of Bioscience and Bioengineering, 92/5 (2001), 405-416, 

<http://www.jstage.jst.go.jp/article/jbb/92/5/405/_pdf>. 

35 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Other Platforms (2006), 

< www1.eere.energy.gov/biomass/other_platforms.html >. 

36 U.S. Environmental Protection Agency, “Landfill Methane Outreach Program,” <http://www.epa.gov/lmop>. 
2. Fee

Any Organic Material

Examples: Agricultural wastes, 

industrial wastes.

Pretreatment: Waste typically s

Qualifications: Dry MSW is fav

be controlled to ensure good be

Final Conversion Technology 

Catalytic Conversion

Any Organic Material

Pretreatment: Sorting

Qualifications: None

Any Organic Material

Pretreatment: Sorting.

Qualifications: Waste must be 

<6 mm (1 to 2 mm. preferred) a

assure high heat transfer rate.

Grains

Mostly: Corn

Pretreatment: Separation of th

the nutrients from the starch

Grains, Sugars and Waste , S

Examples: Grains (corn, sorghu

beets), Beer, and other waste s

Pretreatment: Grinding, cookin

Cellulosic/Woody Biomass 

Pretreatment: Hydrolysis (Dilut

Wet-Mill Fermentation

Dry-Mill Fermentation

Lignocellulosic Biomass Fermentation

Ethanol Production 

14 

Aerobic digestion is a biochemical process through which organic matter is converted to thermal 

energy and fertilizer in the presence of oxygen.37 Aerobic digestion is also called composting. 

Classifying Biomass Conversion Technologies 

This report presents a classification system that is intended to aid in clarifying future discussions of 

biomass conversion technologies. There are three main levels of classification used to catalogue 

conversion technologies in this report. First technologies are classified by method of decomposition, 

then by process specifications, and finally, by engineering design specifications. This cataloguing 

system is illustrated in Figure 6 and is detailed in the following section. 

1. Biomass Conversion 

Technology 

Downdraft Co-Current Fixed Bed 

Updraft Co-Current Fixed Bed 

Cross-Draft Fixed Bed 

Open Core Fixed Bed 

Pressurized Circulating Fluidized Bed 

Atmospheric Circulating Fluidized Bed 

Plasma Arc Gasifier 

2-stage Gasifier 

Open Top 

Aqueous Phase Reforming 

Ablative Fast Pyrolysis 

Cyclonic Fast Pyrolysis 

Rotating Core Fast Pyrolysis 

Open Core Fast Pyrolysis 

Vacuum Pyrolysis 

Flash Pyrolysis 

Thermochemical

Gasification Pyrolysis

Slow

Pyrolysis 

Fast

Pyrolysis 

Novel

Design 

Fluidized

Bed 

Fixed

Bed 

1. Technologies are 

classified according to 

decomposition method 

(platform). 

2. Technologies are 

classified according to 

process specifications. 

3. Technologies are 

classified according 

to engineering design 

specifications. 

Figure 6. Biomass Conversion Technologies 

37 Ohio State University, Extension Bulletin, Bulletin 604-06, Chapter 4, Treatment and Utilization Options for Livestock 

Manure,” Ohio Livestock Manure Management Guide , <http://ohioline.osu.edu/b604/0005.html>; U.S. 

Environmental Protection Agency, “Composting,” <http://www.epa.gov/epaoswer/non-hw/composting/basic.htm>. 
15 

First Classification Level: Method of Decomposition. On the highest level, the matrix classifies 

technologies according to the principal methods of decomposition.38 This classification is illustrated 

in Table 1 below. 

Table 1. Technologies and Methods of Decomposition 

Technology Method of Decomposition 

Thermochemical Uses heat to decompose feedstock into intermediate products. 

Thermochemical conversion technologies include gasification and 

pyrolysis.39 

Biochemical Uses enzymes and bacteria to decompose feedstock into 

intermediate products. Biochemical conversion technologies include 

starch and sugar fermentation, lignocellulosic fermentation, anaerobic 

digestion, landfill gas collection, and aerobic digestion.40 

Chemical Uses chemical reactions to decompose feedstock into intermediate 

products. The principal chemical conversion technology is 

transesterification.41 

Physical processes, such as sorting, shredding, and drying, may sometimes also be necessary to 

prepare feedstock for the main thermochemical or biochemical conversion process.42 

Second Classification Level: Process Specification. Conversion technologies are also classified 

according to process-specific conditions such as presence of oxygen, type of feedstock, and type of 

chemical reaction. This is the level of nomenclature that is most commonly used for policy and 

management publications. In some cases, several different technical classifications could have been 

38 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Biomass Basics (2006), 

<http://www1.eere.energy.gov/biomass/biomass_basics.html>; U.S. Dept. of Energy, Office of Energy Efficiency and 

Renewable Energy, Biomass Program, Other Platforms (2006), <http://www1.eere.energy.gov/biomass/other_plat 

forms.html; Oregon State Department of Energy, Biomass Energy Program Biomass Technology Chart, 

<http://www.oregon.gov/ENERGY/RENEW/Biomass/BiomassHome.shtml#chart>. 

39 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Biomass Basics (2006), 

<http://www1.eere.energy.gov/biomass/biomass_basics.html>. 

40 Ibid. 

41 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Other Platforms (2006), 

<http://www1.eere.energy.gov/biomass/other_platforms.html>. 

42 Phillip C. Badger, Processing Cost Analysis for Biomass Feedstocks (U.S. Dept. of Energy, Oak Ridge National 

Laboratory, 2002), <http://bioenergy.ornl.gov/pdfs/ornltm-2002199.pdf>. 
16 

made, however, one was chosen for the purpose of simplicity and consistency with policy 

publications. This classification is illustrated in Table 2 below. 

Table 2. Technologies and Process Specifications 

Technology Process Specification 

Thermochemical Distinguished by the presence or absence of oxygen in the system.43 

• The presence of oxygen indicates gasification

• The absence of oxygen indicates pyrolysis

Biochemical Distinguished by the type of feedstock.44

• Starch and sugar feedstock indicates starch and sugar fermentation

• Lignocellulosic biomass indicates lignocellulosic fermentation

• Wet feedstocks (typically animal manure) indicate anaerobic 

 digestion

• Drier organic feedstocks indicate aerobic digestion

• Municipal solid wastes indicate landfill gas collection.

Chemical Distinguished by the specific type of chemical reaction which occurs45

• e.g., transesterification

Third Classification Level: Engineering Specifications. Conversion technologies may also be 

distinguished according to engineering design specifications—a level of technical detail not covered 

by most policy and management publications. 

Gasification processes can be loosely categorized as fixed bed, fluidized bed, or “novel” designs. 

These process designs can be modular in nature, facilitating their use in small businesses, rural areas, 

developing countries, and biorefineries.46 These modular designs would also facilitate integration 

43 U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Biomass Basics (2006), 

<http://www1.eere.energy.gov/biomass/biomass_basics.html>. 

44 U.S. Dept. of Energy, Oak Ridge National Laboratory, Bioenergy Feedstock Development Program Bioenergy 

Feedstock Characteristics, <http://bioenergy.ornl.gov/papers/misc/biochar_factsheet.html>; Oregon State Department 

of Energy, Biomass Energy Program Biomass Technology Chart, Oregon: Biomass Energy Program, 

<http://www.oregon.gov/ENERGY/RENEW/Biomass/BiomassHome.shtml#chart>. 

45 Oregon State Department of Energy, Biomass Energy Program, Biomass Technology Chart, 

<http://www.oregon.gov/ENERGY/RENEW/Biomass/BiomassHome.shtml#chart>. 

46 .S. Dept. of Energy, National Renewable Energy Laboratory, Biomass Factsheet: Small Modular Biomass Systems 

(2002), <http://www.nrel.gov/docs/fy03osti/33257.pdf>. 
17 

with other types of technologies in biorefineries. This classification of gasifier engineering design 

specifications is illustrated in Table 3 below. 

Table 3. Gasification Types and Engineering Designs 

Gasification Type Engineering Design 

Fixed Bed Feedstock is placed on a static grate and heated while a 

gasification agent, such as nitrogen, is circulated through the 

gasifier. Variations of fixed bed gasification technologies employ 

different configurations of pressure and gas-flow direction.47 

Examples include downdraft co-current fixed bed gasifier, updraft 

co-current fixed bed gasifier, updraft counter-current fixed bed 

gasifier, cross-draft fixed bed gasifier, and open core fixed bed 

gasifier. 

Fluidized Bed Feedstock is heated and suspended directly in the gasification 

agent, without a static grate. Fluidized bed gasification 

technologies may employ different configurations of pressure and 

gas flow.

48 Examples include pressurized circulating fluidized bed 

gasifier and atmospheric circulating fluidized bed gasifier. 

Novel Designs A category of miscellaneous gasifiers, including the following 

processes: plasma arc gasification, 2-stage gasification, open-top 

gasification, and aqueous phase reforming gasification. 

Pyrolysis processes can be categorized as slow pyrolysis or fast pyrolysis. Fast pyrolysis is currently 

the most widely used pyrolysis system. This classification of pyrolysis system engineering design 

specifications is illustrated in Table 4 below. 

47 Biomass Technology Group (2004), Biomass Gasification, <http://www.btgworld.com/technologies/gasification. 

html>; U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program (2005) Biomass 

Gasification, <http://www1.eere.energy.gov/biomass/gasification.html>; International Energy Agency, Gasification 

Network, Technology (2005), <http://www.gasnet.uk.net/index.php?name=VGVjaG5vbG9neQ==&open=VGVjaG 

5vbG9neQ== >; Alexander Klein. Gasification: an Alternative Process for Energy Recovery and Disposal of 

Municipal Solid Wastes (Unpublished M.S. thesis, Columbia University, 2002), <http://www.seas.columbia.edu/earth/ 

kleinthesis.pdf>.

48 International Energy Agency, Gasification Network, Technology (2005), <http://www.gasnet.uk.net/index. 

php?name=VGVjaG5vbG9neQ==&open=VGVjaG5vbG9neQ== >; Klein, ibid. 
18 

Table 4. Pyrolysis Types and Engineering Designs 

Pyrolysis Type Engineering Design 

Slow Pyrolysis Converts organic material slowly to tar in the complete absence of 

oxygen. Compared to fast pyrolysis, slow pyrolysis is very timeconsuming and produces low yields of tar-derived products.49 

Fast Pyrolysis Converts organic material rapidly to the gaseous state in the 

absence of oxygen, and then condenses the gas into either bio-oil or 

hydrogen.50 Fast pyrolysis processes include open-core fixed bed 

pyrolysis, ablative fast pyrolysis, cyclonic fast pyrolysis, and rotating 

core fast pyrolysis systems. 

Starch and sugar fermentation is a biochemical decomposition process through which glucosecontaining material is chemically decomposed to form ethanol and carbon dioxide. This fermentation 

process can be categorized as either wet-mill or dry-mill fermentation processes. This classification of 

starch and sugar fermentation design specifications is illustrated in Table 5 below. 

Table 5. Starch and Sugar Fermentation Types and Engineering Designs 

Starch and Sugar 

Fermentation Type 

Engineering Design 

Wet Mill The corn is soaked in water or dilute acid to separate the grain 

into its component parts (e.g., starch, protein, germ, oil, kernel 

fibers) before converting the starch to sugars that are then 

fermented to ethanol.51 

Dry Mill The kernels are ground into a fine powder and processed 

without fractionating the grain into its component parts. Most 

ethanol comes from dry milling.52 

Lignocellulosic biomass fermentation is a biochemical decomposition process through which 

lignin-, cellulose-, and/or hemicellulose-containing biomass is chemically decomposed to form 

ethanol and carbon dioxide. Lignocellulosic biomass fermentation processes are similar enough that 

49 Wisconsin Biorefining Development Initiative, Biorefining Process: Fast Pyrolysis (2007), 

<http://www.wisbiorefine.org/proc/fastpyro.pdf>. 

50 International Energy Agency, Pyrolysis Network Overall Fast Pyrolysis Process, <http://www.pyne.co.uk/?_id=71>; 

International Energy Agency, Pyrolysis Network Reactors: Bubbling Fluid Beds, <http://www.pyne.co.uk/?_id=69>; 

U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, Pyrolysis and Other 

Thermal Processing (2005), <http://www1.eere.energy.gov/biomass/pyrolysis.html>. 

51 Wisconsin Biorefining Development Initiative, Biorefining Process: Wet Mill Corn Processing (2007), 

<http://www.wisbiorefine.org/proc/wetcorn.pdf>. 

52 Wisconsin Biorefining Development Initiative, Biorefining Process: Dry Mill Corn Processing (2007), 

<http://www.wisbiorefine.org/proc/drycorn.pdf>. 
19 

they are rarely divided into subtypes. There are several different pretreatment options available for 

lignocellulosic biomass, which are described in greater detail in Appendix C. 

Transesterification is a chemical conversion process through which oils and fats are converted to 

methyl ester, also known as biodiesel. Transesterification is rarely subdivided into further 

classifications. 

Anaerobic digestion processes can be categorized as psychrophilic, mesophilic or thermophilic, 

according to the affinity of bacteria for cool, intermediate or warm temperatures, respectively. This 

classification of anaerobic digester engineering design specifications is illustrated in Table 6 below. 

Table 6. Anaerobic Digestion Types and Engineering Designs 

Anaerobic Digestion 

Type 

Engineering Design53 

Psychrophilic or 

“low-temperature 

digestion” 

The natural decomposition path for manures at temperatures found in 

lagoons. These temperatures vary from about 38 to 85°F (3 to 29°C). 

Biogas production will vary seasonally with variations in lagoon 

temperature. Uncovered lagoons in the U.S. typically operate in the 

psychrophillic range. 

Thermophilic Uses digesters to promote bacteria that grow at temperatures 

between 135 and 155°F (57 to 68°C). These digesters are heated 

and biogas production will not vary seasonally. This type of 

digestion is unusual due to the high cost to maintain temperatures in 

this range. 

Mesophilic Cultivates bacteria that have peak activity between 90 and 105°F (32 

to 40°C). These digesters are heated and biogas production will not 

vary seasonally. Most United States energy-recovery digesters 

operate in the mesophilic range. 

Landfill gas can be collected from sites categorized as bioreactor vessels or landfill sites. These sites 

release methane as a product of the natural or artificial decomposition of landfill material. This 

classification of the engineering design specifications of landfill gas collection sites is illustrated in 

Table 7 below. 

53 Energy and Environmental Analysis, Inc. and Eastern Research Group, Inc. Biomass Combined Heat and Power 

Catalog of Technologies. Washington: U.S. Environmental Protection Agency Office of Air and Radiation, Combined 

Heat and Power Partnership, 2007 (unpublished draft) 
20 

Table 7. Landfill Gas Collection Types and Engineering Designs

Landfill Gas 

Collection Type 

Engineering Design 

Bioreactor Vessels A landfill that is manipulated with the addition of liquid or air, so as 

to facilitate rapid decomposition54 This optimization of the natural 

decomposition process results in rapid gas formation. 

Landfill Sites Traditional locations of solid waste disposal in the United States. 

These sites can include sanitary landfills and sanitary landfills 

re-circulating leachate.55 

Aerobic digestion processes can be categorized as static pile, enclosed compost, in-vessel compost, 

and turned wind-roll composting systems. Some designs can also be modular, for easy application to 

small business operations, rural areas, developing countries, and biorefineries. These methods can be 

used in conjunction with many facilities, including aerobic digestion of biosolids from wastewater 

treatment plants.56 This classification of aerobic digestion engineering design specifications is 

illustrated in Table 8 below. 

Table 8. Landfill Gas Collection Types and Engineering Designs 

Aerobic Digestion 

Type 

Engineering Design57 

Static pile 

(passive windrow) 

A low-tech and labor-efficient approach to making compost. However, 

the process is time-intensive, as compost is produced by natural 

aeration. 

Enclosed compost 

vessel 

(bin compost) 

A low-tech, moderately labor-efficient approach to making compost. The 

compost is formed through natural aeration and turning. 

In-vessel 

compost system 

Produces compost in drums or other vessels. The system is a high-tech 

and labor efficient approach, as the vessels are aerated automatically 

with machines. 

Turned windrow 

compost system 

Produces compost in piles. The piles are mechanically aerated and are 

thus a low-tech and medium-labor option. 

54 U.S. Environmental Protection Agency, Office of Solid Waste, Municipal Solid Waste: Bioreactors (2006), 

<http://www.epa.gov/epaoswer/non-hw/muncpl/landfill/bioreactors.htm>. 

55 Energy and Environmental Analysis, Inc. and Eastern Research Group, Inc., op. cit. 

56 U.S. Environmental Protection Agency, Biosolids Generation, Use, and Disposal in the United States (1999), 

<http://www.epa.gov/epaoswer/non-hw/compost/biosolid.pdf>. 

57 British Columbia (Canada) Ministry of Agriculture, Food, and Fisheries, Composting Factsheet: Composting Methods 

(1996), <http://www.agf.gov.bc.ca/resmgmt/publist/300series/382500-5.pdf>. 
3. Products

Vacuum Pyrolysis

Flash Pyrolysis

Any Organic Material

1. Biomass Conversion 

Technology 2. Feedstocks 

Downdraft Co-Current Fixed Bed 

Updraft Co-Current Fixed Bed 

Cross-Draft Fixed Bed 

Open Core Fixed Bed 

Pressurized Circulating Fluidized Bed 

Atmospheric Circulating Fluidized Bed 

Plasma Arc Gasifier 

2-stage Gasifier 

Open Top 

Aqueous Phase Reforming 

Ablative Fast Pyrolysis 

Cyclonic Fast Pyrolysis 

Rotating Core Fast Pyrolysis 

Open Core Fast Pyrolysis 

Any Organic Material 

Examples: Agricultural wastes, hazardous organic wastes, 

industrial wastes. 

Pretreatment: Waste typically segregated. 

Qualifications: Dry MSW is favorable. Coal size distribution must 

be controlled to ensure good bed permeability. 

Final Conversion Technology (Optional): Fischer-Tropsch 

Catalytic Conversion 

Any Organic Material 

Pretreatment: Sorting 

Qualifications: None

Thermochemical

Gasification Pyrolysis 

Fast

Pyrolysis 

Novel

Design 

Fluidized

Bed 

Fixed

Bed 

4. (Optional) Final 

conversion 

technology 

Figure 7. Feedstocks for Biofuels, Bioenergy, and Bioproducts 

(See Appendix C for greater detail.) 

Pretreatment: Sorting.

Qualifications: Waste must be pre-sorted and processed to

<6 mm (1 to 2 mm. preferred) and <10% moisture content to

assure high heat transfer rate.

Intermediate Products: Combustible gases, liquids, tar

inert fluidizing gases.

Final Products: Electricity, Thermal Energy, Hydrogen, 

and other alcohols, Diesel type fuels, Gasoline.

Co-products: Charcoal, Ash, Carbon Dioxide.

Intermediate products: Syngas and Charcoal

Final Products: Bio-Oil and Charcoal

Co-products: Electricity and Thermal Energy

Intermediate Products: Mash, Sugar

Final Products: Ethanol

Co-products: Distillers grains plus solubles, Carbon Dio

Intermediate Products: Starch, Sugar

Final Products: Ethanol

Co-products: Corn oil, corn gluten meal, corn gluten fee

dioxide, liquid bio-fertilizers

Intermediate Products: Cellulose, hemicellulose. lignin

Final Products: Ethanol

Co-products: Carbon Dioxide, residual cellulose and lig

electricity and thermal energy

Grains

Mostly: Corn

Pretreatment: Separation of the oil, protein, fiber and the bulk of

the nutrients from the starch

Grains, Sugars and Waste , Starches and Sugars

Examples: Grains (corn, sorghum, barley), Sugars (Sugarcane and 

beets), Beer, and other waste sugars and starches.

Pretreatment: Grinding, cooking and fermentation

Cellulosic/Woody Biomass 

Pretreatment: Hydrolysis (Dilute Acid, Concentrated Acid, 

Enzymatic, Steam explosion)

Wet-Mill Fermentation

Dry-Mill Fermentation

Lignocellulosic Biomass Fermentation

Biochemical 

ical

Ethanol Production Anaerobic Digesters Landfill Aerobic 

oduction

Mesophilic Process or Thermophilic

Process

Slow 

Pyrolysis

Anaerobic activated sludge process 

Anaerobic clarigester

Anaerobic contact process 

Anaerobic expanded-bed reactor 

Anaerobic filter

Anaerobic fluidized bed 

Anaerobic lagoon

Anaerobic migrating blanket reactor 

Batch system anaerobic digester 

Expanded granular sludge bed digestion

Hybrid reactor 

Imhoff tank 

One-stage anaerobic digester 

Submerged media anaerobic reactor 

Two-stage anaerobic digester 

Upflow anaerobic sludge blanket digestion

Upflow and down-flow anaerobic attached 

growth 

Bioreactor vessel

Landfill Site

Static Pile

Enclosed Compost

Turned Window

In-Vessel Compost

Transesterification

Practically any Organic Waste

Pretreatment: Sorting

Qualifications: A separation between organic and contaminants is

necessary.

Oils, fats, used cooking oils, greases, methanol or ethanol and 

a catalyst

Pretreatment: Used cooking oils, yellow greases, and some tree 

oils are taken through an esterification process to remove fatty acid 

Organic Wastes

Pretreatment: Sorting pre-treatment

Qualifications: The waste must be contained, compacted and 

covered in a vessel

Organic Wastes

Pretreatment: None Qualifications: None

Intermediate Products: Oils fats or greases taken throu

transesterfication

Intermediate products: None

Final Products: Valuable Compost

Co-products: Heat and Carbon Dioxide. (May be usefu

greenhouse environment or for heating)

Intermediate products: Biogas composed of Methane, 

Dioxide, Nitrogen, Hydrogen, Hydrogen Sulfide and Oxy

Final Products: Electricity, thermal energy, methane. C

for vehicle fuel.

Co-products: Carbon Dioxide for possible use in greenh

operations, and Biofertilizers.

Intermediate products: N/A.

Final Products: Biogas, Thermal Energy, Digestate.

Co-products: Liquid and Solid Biofertilizers.

Almost any organic material: paper, grass clippings, leftover food,

sewages, animal wastes; and other forms of biomass such as

distillers grains.

Pretreatment: Sorting or screening to remove inorganic material.

Qualifications: The material may need to be pre-processed and 

water added.

21 

Feedstock and Pretreatment 

Conversion technologies are designed to accept specific types of feedstock for optimal processing. 

Feedstocks can include oils, fats, greases, sludge, sugars, starches, lignocellulosic biomass, biosolids, 

municipal solid waste, and woody biomass. These feedstocks are included in the Appendix C matrix, 

as illustrated below in Figure 7. 

1. Feedstock 

classification and 

examples for 

each technology 

2. Feedstock 

pretreatment for 

each technology 

3. Feedstock 

qualifications for 

each technology 

Particular feedstocks may also need to be prepared through specific physical processes, such as 

sorting, shredding, hydrolysis, or drying. This section also discusses the feedstocks appropriate for 

certain technologies, and includes pretreatment options and feedstock qualifications. 

Gasification systems can accept any organic material, including agricultural wastes, black liquor 

from pulping operations, hazardous organic wastes, and industrial wastes. Dry, uniformly sized 

organic material is preferable. This organic material is typically segregated in a pretreatment process 

before gasification.58 

Pyrolysis systems can accept any organic material, including agricultural wastes and municipal solid 

wastes. For fast pyrolysis systems, dry, sorted, and homogeneously sized (<6mm) organic material 

typically achieves a high heat transfer rate.59 

Starch and sugar fermentation systems can accept any sugar- or starch-containing material such as 

grains, sugarcane, beets, beer, and waste sugars. Typically, wet-mill fermentation uses grains, while 

dry-mill fermentation uses grains, sugars, starches, and sugar wastes. In wet-mill fermentation, grains 

58 Emanuele Scoditti and N. Parker, “IEA Bioenergy Agreement, Task 33: Thermal Gasification of Biomass, Review of 

Energy Conversion Devices” (2003), < http://media.godashboard.com/gti/IEA/ReviewofEnergyConversionDevicesrev. 

pdf>.; Wisconsin Biorefining Development Initiative, Biorefining Process: Biomass Gasification (2007), 

<http://www.wisbiorefine.org/proc/biomassgas.pdf>. 

59 Wisconsin Biorefining Development Initiative, Biorefining Process: Fast Pyrolysis (2007), 

<http://www.wisbiorefine.org/proc/fastpyro.pdf>. 
22 

are preprocessed, so as to separate the oil, protein, fiber, and nutrients from the starch. In dry-mill 

fermentation, the grains are grinding and cooking before fermentation.60 

Lignocellulosic biomass fermentation systems can accept any lignin-, cellulose-, and/or 

hemicellulose-containing material, including forest residue, crop residue, and switchgrass. 

Lignocellulosic material should be preprocessed in order to break lignocellulosic material into sugars. 

This is most commonly achieved though hydrolysis, a process in which water is used to break apart 

a chemical compound. Common types of hydrolysis include dilute acid hydrolysis, concentrated acid 

hydrolysis, enzymatic hydrolysis, and steam explosion.61 

Transesterification systems can accept any oil, fat, or grease, including used cooking oils, animal 

fat, and plant oils. Typically, feedstocks with fatty acid content exceeding 4 percent must be 

pretreated in an esterification process—a chemical process that reduces the fatty acids in the 

feedstock to an acceptable concentration for the transesterification reaction.62 

Anaerobic digestion systems can accept any organic material, including sewage, animal wastes, 

grass clippings, and paper. Wet organic material is favorable, and water may be used to moisten dry 

material. The material may need to be preprocessed to remove inorganic material.63 

Landfill gas collection systems can accept any organic material, including agricultural wastes, and 

organic municipal solid wastes. Because landfill gas is a product of natural decomposition, the higher 

the organic content of the waste, the more methane is produced. This organic material is typically 

segregated before being landfilled. 

Aerobic digestion systems can accept any organic material, including agricultural wastes, manures, 

and food waste. The organic material is typically separated from inorganic contaminants before being 

digested.64 

Final Processing: Intermediate, Final, and Co-products 

Intermediate products consist of output from the primary conversion processes; these intermediate 

products require further processing to obtain the desired final products. Principal intermediate products include: pyrolytic bio-oil, combustible gas, inert gases, pelletized feedstock, fertilizer, lipids, 

biodiesel, steam, methane, ethanol, and butanol. These products are then processed and converted 

into the desired final energy product using technologies such as turbines, engines, and boilers. The 

final products that result from this processing and conversion include electricity, heat, and fuel. 

60 Wisconsin Biorefining Development Initiative, Biorefining Process: Dry Mill Corn Processing (2007) <http://www. 

wisbiorefine.org/proc/drycorn.pdf>; ibid, Biorefining Process: Wet Mill Corn Processing, <http://www.wisbiorefine. 

org/proc/wetcorn.pdf>.; ibid, Biorefining Process: Fermentation of 6-Carbon Sugars and Starches, 

<http://www.wisbiorefine.org/proc/fermentss.pdf>. 

61 Wisconsin Biorefining Development Initiative, Biorefining Process: Fermentation of Lignocellulosic Biomass (2007), 

<http://www.wisbiorefine.org/proc/fermlig.pdf>. 

62 Wisconsin Biorefining Development Initiative, Biorefining Process: Esterification/ Transesterification (2007), 

<http://www.wisbiorefine.org/proc/ester.pdf>. 

63 Wisconsin Biorefining Development Initiative, Biorefining Process: Anaerobic Digestion (20007), 

<http://www.wisbiorefine.org/proc/anaerobic.pdf>. 

64 Wisconsin Biorefining Development Initiative, Biorefining Process: Aerobic Digestion/ Composting (2007), 

<http://www.wisbiorefine.org/proc/aerobic.pdf>. 
Co-products, also called biobased products, are products output from the primary conversion process 

that require minimal or no further processing. Co-products may have substantial economic value that 

adds to the proceeds from the principal energy product being sought. These products include 

chemical feedstock, animal feed, food items, charcoal, and fertilizers. 

Table 9 below illustrates these intermediate, final, and co-products. 

Table 9. Technologies and Intermediate, Co-products, and Final Products 

Technology Intermediate Products Bio-based Co-products Final Products 

Gasification Combustible gases 

Combustible liquids 

Combustible tars 

Inert fluidized gases 

Charcoal 

Ash 

Carbon dioxide 

Electricity 

Heat 

Fuel 

Pyrolysis Syngas 

Bio-oil 

Charcoal 

Charcoal 

Non-combustible gases 

Electricity 

Heat 

Starch and Sugar 

Fermentation 

Wet-mill 

glucose 

fermentation 

Mash 

and 

sugar 

Distillers grains 

Carbon dioxide 

Fuel 

Electricity 

Heat 

Dry-mill 

glucose 

fermentation 

Starch 

and 

sugar 

Corn oil 

Corn gluten meal 

Corn gluten feed 

Carbon dioxide 

Liquid biofertilizers 

Lignocellulosic 

Biomass 

Fermentation 

Cellulose 

Hemicellulose 

Lignin 

Carbon dioxide 

Residual cellulose and 

Lignin 

Fuel 

Electricity 

Heat 

Transesterification n/a Methyl ester (biodiesel), 

Methanol, Glycerin (for 

soaps, lubricants, and 

chemical feedstock) 

Fuel 

Electricity 

Heat 

Anaerobic 

Digestion 

Biogas 

Thermal energy 

Digestate 

Liquid fertilizers 

Solid fertilizers 

Electricity 

Heat 

Landfill Gas 

Collection 

Biogas (a mixture of 

methane, carbon dioxide, nitrogen, hydrogen, 

oxygen, and hydrogen 

sulfide) 

Carbon dioxide 

Uncomposted refuse 

Biofertilizers 

(Co-products of landfill 

gas processing minimal) 

Electricity 

Heat 

Aerobic Digestion Heat and fertilizer Carbon Dioxide Heat 

23 
Ablative Fast Pyrolysis

Cyclonic Fast Pyrolysis

Rotating Core Fast Pyrolysis

Open Core Fast Pyrolysis

Vacuum Pyrolysis

Flash Pyrolysis

Any Organic Material

Pretreatment: Sorting

Qualifications: None

Any Organic Material

Pretreatment: Sorting.

Qualifications: Waste must be pre-sorted and processed to

<6 mm (1 to 2 mm. preferred) and <10% moisture content to

assure high heat transfer rate.

Intermediate products: Syngas and Charcoal

Final Products: Bio-Oil and Charcoal

Co-products: Electricity and Thermal Energy

Intermediate Products: Mash, Sugar

Final Products: Ethanol

Co-products: Distillers grains plus solubles, Carbon Dioxide

Intermediate Products: Starch, Sugar

Final Products: Ethanol

Co-products: Corn oil, corn gluten meal, corn gluten feed, carbon 

dioxide, liquid bio-fertilizers

Intermediate Products: Cellulose, hemicellulose. lignin

Final Products: Ethanol

Co-products: Carbon Dioxide, residual cellulose and lignin,

electricity and thermal energy

Grains

Mostly: Corn

Pretreatment: Separation of the oil, protein, fiber and the bulk of

the nutrients from the starch

Grains, Sugars and Waste , Starches and Sugars

Examples: Grains (corn, sorghum, barley), Sugars (Sugarcane and 

beets), Beer, and other waste sugars and starches.

Pretreatment: Grinding, cooking and fermentation

Cellulosic/Woody Biomass 

Pretreatment: Hydrolysis (Dilute Acid, Concentrated Acid, 

Enzymatic, Steam explosion)

Wet-Mill Fermentation

Dry-Mill Fermentation

Lignocellulosic Biomass Fermentation

1. Biomass Conversion 

Technology 2. Feedstocks 3. Products 

Thermochemical

Gasification 

Fixed

Bed 

Downdraft Co-Current Fixed Bed 

Updraft Co-Current Fixed Bed 

Cross-Draft Fixed Bed 

Open Core Fixed Bed Any Organic Material 

Examples: Agricultural wastes, hazardous organic wastes, 

industrial wastes. 

Pretreatment: Waste typically segregated. 

Qualifications: Dry MSW is favorable. Coal size distribution must 

be controlled to ensure good bed permeability. 

Final Conversion Technology (Optional): Fischer-Tropsch 

Catalytic Conversion

Intermediate Products: Combustible gases, liquids, tars, and 

inert fluidizing gases. 

Final Products: Electricity, Thermal Energy, Hydrogen, Ethanol 

and other alcohols, Diesel type fuels, Gasoline. 

Fluidized

Co-products: Charcoal, Ash, Carbon Dioxide. 

Bed 

Pressurized Circulating Fluidized Bed 

Atmospheric Circulating Fluidized Bed 

Novel

Design 

Plasma Arc Gasifier 

2-stage Gasifier 

Open Top 

Aqueous Phase Reforming 

Biochemical 

ical

Pyrolysis Ethanol Production Anaerobic Digesters Landfill Aerobic 

oduction

Mesophilic Process or Thermophilic

Process

Slow 

Pyrolysis

Fast 

Pyrolysis

Anaerobic activated sludge process 

Anaerobic clarigester

Anaerobic contact process 

Anaerobic expanded-bed reactor 

Anaerobic filter

Anaerobic fluidized bed 

Anaerobic lagoon

Anaerobic migrating blanket reactor 

Batch system anaerobic digester 

Expanded granular sludge bed digestion

Hybrid reactor 

Imhoff tank 

One-stage anaerobic digester 

Submerged media anaerobic reactor 

Two-stage anaerobic digester 

Upflow anaerobic sludge blanket digestion

Upflow and down-flow anaerobic attached 

growth 

Bioreactor vessel

Landfill Site

Static Pile

Enclosed Compost

Turned Window

In-Vessel Compost

Transesterification

Practically any Organic Waste

Pretreatment: Sorting

Qualifications: A separation between organic and contaminants is

necessary.

Oils, fats, used cooking oils, greases, methanol or ethanol and 

a catalyst

Pretreatment: Used cooking oils, yellow greases, and some tree 

oils are taken through an esterification process to remove fatty acid 

Organic Wastes

Pretreatment: Sorting pre-treatment

Qualifications: The waste must be contained, compacted and 

covered in a vessel

Organic Wastes

Pretreatment: None Qualifications: None

Intermediate Products: Oils fats or greases taken through 

transesterfication

Intermediate products: None

Final Products: Valuable Compost

Co-products: Heat and Carbon Dioxide. (May be useful in a 

greenhouse environment or for heating)

Intermediate products: Biogas composed of Methane, Carbon 

Dioxide, Nitrogen, Hydrogen, Hydrogen Sulfide and Oxygen.

Final Products: Electricity, thermal energy, methane. CNG or LNG 

for vehicle fuel.

Co-products: Carbon Dioxide for possible use in greenhouse 

operations, and Biofertilizers.

Intermediate products: N/A.

Final Products: Biogas, Thermal Energy, Digestate.

Co-products: Liquid and Solid Biofertilizers.

Almost any organic material: paper, grass clippings, leftover food,

sewages, animal wastes; and other forms of biomass such as

distillers grains.

Pretreatment: Sorting or screening to remove inorganic material.

Qualifications: The material may need to be pre-processed and 

water added.

More detailed information on intermediate, final, and co-products can also be obtained from the 

Appendix C matrix, as indicated in Figure 8 below. 

Intermediate and Coproducts are detailed in 

the “Products” column 

Figure 8. Intermediate and Co-products in the Biomass Conversion Matrix 

Energy Conversion Processes 

In the previous section, the various products of conversion technologies were outlined, and 

intermediate, final, and co-products were defined. The section also suggested that various energy 

conversion processes must be employed in order to convert intermediate products to final energy 

products and co-products such as electricity, heat, fuels, and chemical feedstock. The accompanying 

matrix does not currently outline in detail the technologies that convert intermediate products to 

variable energy and co-products. In many cases, the technologies are well understood and developed 

and thus were not selected as the focus of this report. However, the following section will briefly 

outline the methods through which intermediate products are converted to final energy and 

co-products. 

Table 10 below illustrates some of the conversion methods frequently employed to convert 

intermediate products into final energy and co-products. 

24 
Table 10. Intermediate Products, Energy Conversion Methods, and Final Products 

Intermediate Product Energy Conversion Method Final Product (Energy and 

Co-Products) 

Biodiesel n/a Chemical Feedstock 

Glycerin Chemical processing 

Cellulose, Hemicellulose, 

and Lignin 

1. Hydrolysis 

2. Fermentation 

Mash and sugar Fermentation (and often, 

subsequent distillation) 

Distillers grains, corn 

gluten feed 

Processing Co-Product (Animal feed and 

other food products) 

Carbon Dioxide n/a Co-product (Industrial Use) 

Bio oil Combustion Electricity 

Heat 

Biodiesel Combustion 

Cellulose, Hemicellulose, 

and Lignin 

1. Hydrolysis 

2. Fermentation 

3. Combustion 

Combustible Biogas Combustion 

Combustible gases (from 

gasification, anaerobic 

digestion, or landfill gas 

collection) 

Combustion 

Mash and sugar 1. Fermentation (and often, 

subsequent distillation) 

2. Combustion 

Combustible liquids Combustion Electricity 

Combustible tars Combustion 

Inert noncombustible 

gases (syngas from 

gasification, pyrolysis, 

anaerobic digestion, or 

landfill gas collection) 

Turbine 

25 
Table 10. (continued) 

Intermediate Product Energy Conversion Method Final Product (Energy 

and Co-Products) 

Liquid and Solid Fertilizers n/a Fertilizer 

Digestate n/a 

Charcoal n/a 

Biodiesel n/a Fuel (Biodiesel) 

Cellulose, Hemicellulose, 

and Lignin 

1. Hydrolysis 

2. Fermentation 

Fuel (Ethanol) 

Inert noncombustible gases 

(syngas) 

Fischer-Tropsch Catalytic 

Conversion 

Mash and sugar Fermentation (and often, 

subsequent distillation) 

Thermal Energy Boiler system Heat 

It is important to understand the variety of energy production capabilities for all conversion 

technologies. Some technologies yield a wide variety of high-value end products, while others yield 

few. However, both have viable applications. For example, gasification systems may be appropriate 

for disaster clean-up, because they accept a wide variety of feedstocks and because their final and 

co-products have a wide variety of applications (e.g., fuel, electricity, heat, and chemical 

feedstocks).65 Conversely, in the case of more particular technologies such as anaerobic digestion, 

the distribution of the final product is often an issue. 

26 

65 Emanuele Scoditti and N. Parker, “IEA Bioenergy Agreement, Task 33: Thermal Gasification of Biomass, Review of 

Energy Conversion Devices” (2003), < http://media.godashboard.com/gti/IEA/ReviewofEnergyConversionDevices 

rev.pdf>. 
Appendix A. 

Selected Online Resources

BIOconversion Blog. An online journal that covers international issues, facility deployments, and 

new developments, at <http://bioconversion.blogspot.com>. Three other three related blogs are 

BIOstock Blog at <http://biostock.blogspot.com>, BIOoutput Blog at <http://biooutput.blogspot. 

com/>, and BIOwaste Blog. <http://biowaste.blogspot.com>. 

Bioenergy Feedstock Information Network (BFIN). A gateway to biomass feedstock information 

resources from the U.S. Department of Energy, DOE national laboratories, and other research 

organizations. <http://bioenergy.ornl.gov/main.aspx>. 

Bioenergy Wiki. An open electronic forum to promote the utilization of bioenergy in a sustainable 

manner. It advances understanding of relevant issues and facilitates sharing of information, views and 

experience. <http://www.bioenergywiki.net/>. 

Biomass Energy Center (BEC). A UK site providing links to information on fuel processing and 

supply chains, emphasizing woodfuel and heat production; also offers a query service focusing on 

biomass fuel types that are commercially available or being researched. 

<http://www.biomassenergycentre.org.uk/portal/page?_pageid=73,1&_dad=portal&_ 

schema=PORTAL>. 

Biomass Program of the Department of Energy. A site describing the development of technology 

for converting biomass to fuels, chemicals, materials, and power, thus fostering growth of 

biorefineries and reducing dependence on imported oil. <http://www1.eere.energy.gov/biomass>. 

California Biomass Collaborative. An organization based at the University of California, Davis 

aimed at enhancing the sustainable management and development of biomass in California. <http:// 

biomass.ucdavis.edu>. 

California Biomass Facilities Reporting System (BFRS). A source of extensive searchable data on 

California biomass facilities and other resources. <http://cbc2.ucdavis.edu>. 

Conversion and Biomass to Energy. A site of the California Integrated Waste Management Board. 

<http://www.ciwmb.ca.gov/organics/conversion>. 

Gasifier Inventory. An overview of existing biomass gasifier installations and accompanying 

manufacturers. Users submit an input form for access to the database. <http://www.gasifiers.org>. 

Great Lakes Biomass State-Regional Partnership. One of five regional programs supported by the 

U.S. Department of Energy to encourage greater production and use of biomass for energy 

generation. <http://www.cglg.org/biomass/index.asp>. (Others are the Northeast Regional Biomass 

27 
Program <http://www.nrbp.org>; Pacific Regional Biomass Energy Partnership <http://www.pacificbiomass.org>; Southeastern Regional Biomass Partnership <http://www.serbep.org>; and Western 

Regional Biomass Energy Program <http://www.westgov.org/wga/initiatives/biomass>). 

IEA Bioenergy. An organization established by the International Energy Agency in 1978 to 

accelerate use of environmentally sound and cost-competitive bioenergy on a sustainable basis. 

<http://www.ieabioenergy.com>. 

Oregon Department of Energy: Biomass Energy. A site providing general and detailed information 

in the technology and development of biomass energy. <http://www.oregon.gov/ENERGY/RENEW/ 

Biomass/BiomassHome.shtml>. 

Phyllis: The Composition of Biomass and Waste. A database created by the Netherlands Energy 

Research Center, which enables users to analyze data on individual biomass or waste materials and to 

obtain the average composition of any combination of groups or subgroups. 

<http://www.ecn.nl/phyllis>. 

U.S. Environmental Protection Agency. Several EPA-managed bioenergy technical assistance 

programs promote the development of bioenergy products that reduce greenhouse gas emissions. 

The AgStar program encourages the use of methane recovery (biogas) at confined animal feeding 

operations (“CAFO”) that manage manure as liquids or slurries <www.epa.gov/agstar>. The Landfill 

Method Outreach Program (LMOP) promotes the use of landfill gas as a renewable green energy 

source <www.epa.gov/lmop>. The Combined Heat and Power (CHP) Partnership fosters the use 

of highly efficient biomass CHP and other CHP systems <www.epa.gov/chp>. 

Wisconsin Biorefining Development Initiative. An introduction to biorefining processes that can 

transform low-value biobased feedstocks into multiple, higher-value biobased products. 

<http://www.wisbiorefine.org/index.html>. 

28 
Appendix B. 

Ethanol Production Technologies

Ethanol can be produced from several types of feedstocks. Starch and sugars can be directly 

fermented with minimal pretreatment, as illustrated in Figure 9 below. 

Figure 9. Ethanol Production from Starches and Sugars 

Starches and 

Sugars (e.g. 

grain, seed) 

Fermentation 

Process Ethanol 

However, lignocellulosic biomass, which is comprised of Lignin, Cellulose, and Hemicellulose, 

requires more pretreatment before it can be fermented. Thus, in the process of lignocellulosic biomass 

fermentation, the feedstock must first be pretreated with hydrolysis or one of several other treatments. 

Pretreatment breaks the feedstock into component sugars, where it can then be fermented as in starch 

and sugar fermentation above. Due to national goals for cellulosic ethanol this pretreatment step in 

currently being intensively researched, especially the development of special enzymes and genetic 

modifications.66 This process is illustrated in Figure 10 below: 

Figure 10. Pretreatment of Cellulosic Biomass 

Lignocellulosic 

Biomass Pretreatment Fermentation Ethanol 

66 U.S Department of Energy (2006) Breaking the Biological Barriers to Cellulosic Ethanol: A Joint Research Agenda. 

Washington, DC: Department of Energy, Offices of Science/Energy Efficiency and Renewable Energy. 

http://genomicsgtl.energy.gov/biofuels/2005workshop/2005low_feedstocks.pdf 

29 
Appendix C. 

Biomass Conversion Matrix

1. Biomass Conversion 

Technology 2. Feedstocks 3. Products 

Thermochemical

Gasification

Fixed

Bed 

Downdraft Co-Current Fixed Bed 

Updraft Co-Current Fixed Bed 

Cross-Draft Fixed Bed 

Open Core Fixed Bed Any Organic Material 

Examples: Agricultural wastes, hazardous organic wastes, 

industrial wastes. 

Pretreatment: Waste typically segregated. 

Qualifications: Dry MSW is favorable. Coal size distribution must 

be controlled to ensure good bed permeability. 

Final Conversion Technology (Optional): Fischer-Tropsch 

Catalytic Conversion 

Intermediate Products: Combustible gases, liquids, tars, and 

inert fluidizing gases. 

Final Products: Electricity, Thermal Energy, Hydrogen, Ethanol 

and other alcohols, Diesel type fuels, Gasoline. 

Fluidized

Co-products: Charcoal, Ash, Carbon Dioxide. 

Bed

Pressurized Circulating Fluidized Bed 

Atmospheric Circulating Fluidized Bed 

Novel

Design

Plasma Arc Gasifier 

2-stage Gasifier 

Open Top 

Aqueous Phase Reforming 

Pyrolysis

Fast

Pyrolysis

Ablative Fast Pyrolysis 

Cyclonic Fast Pyrolysis 

Rotating Core Fast Pyrolysis 

Open Core Fast Pyrolysis 

Any Organic Material 

Pretreatment: Sorting 

Qualifications: None Intermediate products: Syngas and Charcoal 

Final Products: Bio-Oil and Charcoal 

Co-products: Electricity and Thermal Energy 

Slow

Pyrolysis

Vacuum Pyrolysis 

Flash Pyrolysis 

Any Organic Material 

Pretreatment: Sorting. 

Qualifications: Waste must be pre-sorted and processed to 

<6 mm (1 to 2 mm. preferred) and <10% moisture content to 

assure high heat transfer rate. 

Biochemical

Ethanol Production

Wet-Mill Fermentation 

Grains 

Mostly: Corn 

Pretreatment: Separation of the oil, protein, fiber and the bulk of 

the nutrients from the starch 

Intermediate Products: Mash, Sugar 

Final Products: Ethanol 

Co-products: Distillers grains plus solubles, Carbon Dioxide 

Dry-Mill Fermentation 

Grains, Sugars and Waste , Starches and Sugars 

Examples: Grains (corn, sorghum, barley), Sugars (Sugarcane and 

beets), Beer, and other waste sugars and starches. 

Pretreatment: Grinding, cooking and fermentation 

Intermediate Products: Starch, Sugar 

Final Products: Ethanol 

Co-products: Corn oil, corn gluten meal, corn gluten feed, carbon 

dioxide, liquid bio-fertilizers 

Lignocellulosic Biomass Fermentation 

Cellulosic/Woody Biomass 

Pretreatment: Hydrolysis (Dilute Acid, Concentrated Acid, 

Enzymatic, Steam explosion) 

Intermediate Products: Cellulose, hemicellulose. lignin 

Final Products: Ethanol 

Co-products: Carbon Dioxide, residual cellulose and lignin, 

electricity and thermal energy 

Anaerobic Digesters

Mesophilic Process or Thermophilic

Process 

Anaerobic activated sludge process 

Anaerobic clarigester 

Anaerobic contact process 

Anaerobic expanded-bed reactor 

Anaerobic filter 

Anaerobic fluidized bed 

Anaerobic lagoon 

Anaerobic migrating blanket reactor 

Batch system anaerobic digester 

Expanded granular sludge bed digestion 

Hybrid reactor 

Imhoff tank 

One-stage anaerobic digester 

Submerged media anaerobic reactor 

Two-stage anaerobic digester 

Upflow anaerobic sludge blanket digestion 

Upflow and down-flow anaerobic attached 

growth 

Almost any organic material: paper, grass clippings, leftover food, 

sewages, animal wastes; and other forms of biomass such as 

distillers grains. 

Pretreatment: Sorting or screening to remove inorganic material. 

Qualifications: The material may need to be pre-processed and 

water added. 

Intermediate products: N/A. 

Final Products: Biogas, Thermal Energy, Digestate. 

Co-products: Liquid and Solid Biofertilizers. 

Landfill

Bioreactor vessel 

Organic Wastes 

Pretreatment: Sorting pre-treatment 

Qualifications: The waste must be contained, compacted and 

covered in a vessel 

Intermediate products: Biogas composed of Methane, Carbon 

Dioxide, Nitrogen, Hydrogen, Hydrogen Sulfide and Oxygen. 

Final Products: Electricity, thermal energy, methane. CNG or LNG 

for vehicle fuel. 

Co-products: Carbon Dioxide for possible use in greenhouse 

operations, and Biofertilizers. Landfill Site 

Organic Wastes 

Pretreatment: None Qualifications: None 

Aerobic

Static Pile 

Enclosed Compost 

Turned Window 

In-Vessel Compost 

Transesterification 

Practically any Organic Waste 

Pretreatment: Sorting 

Qualifications: A separation between organic and contaminants is 

necessary. 

Intermediate products: None 

Final Products: Valuable Compost 

Co-products: Heat and Carbon Dioxide. (May be useful in a 

greenhouse environment or for heating) 

Chemical

Biodiesel Production

Oils, fats, used cooking oils, greases, methanol or ethanol and 

a catalyst 

Pretreatment: Used cooking oils, yellow greases, and some tree 

oils are taken through an esterification process to remove fatty acid 

that should, preferably, be reduced to less than 1% (at least below 

4%). 

Qualifications: Essentially any bio-oil, animal fat or tallow, used 

cooking oil, yellow/trap grease, plant or tree oil can be converted 

into biodiesel if the fatty acid content is low enough. 

Intermediate Products: Oils fats or greases taken through 

transesterfication 

Final Products: Biodiesel 

Co-products: Glycerin, Soaps 

30 
PRESORTED STANDARD 

POSTAGE & FEES PAID 

EPA 

PERMIT NO. G-35 

Office of Research and Development 

Sustainability Program Washington, DC 20460 

Official Business 

Penalty for Private Use 

$300 

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December 2007 

www.epa.gov