Types of Biomass

Domestic biomass resources include biomass processing residues including pulp and paper operation, agricultural and forestry wastes, urban wood wastes, municipal solid wastes and landfill gas, animal wastes and terrestrial and aquatic crops grown solely for energy purposes, known as energy crops [1]. In large quantities, the biomass source is called a feedstock. Making use of the waste is more productive than allowing it to sit and decompose on its own, which is sometimes even more hazaradous to the surrounding environment. Below is a more detailed description of each of these types.

(Below) Biomass Samples from the NREL Biomass Research Website

Biomass Processing Residues. All processing of biomass yields byproducts and waste streams collectively called residues, which have significant energy potential. Not all residues can be used for electricity generation, some must be used to replenish the source with nutrients or elements. Still, residues are simple to use because they have already been collected.

• Pulp and paper operation residues. Plants are made up of lignin, hemicellulose and cellulose fiber [2]. Because of its chemical and physical properties, lignin breaks down much easier than cellulose. Pulping is the separation and breaking down of the lignin fibers of a plant in order to "suspen[d] the cellulose fibers" to create paper. [2] Leftover pulp creates a residue. These residues are the byproducts of logging and processing operations. Processing of wood for products produces sawdust and a collection of bark, branches and leaves/needles chipped or pulped. In general, paper mills utlize their pulp residue to create energy for the paper mill, which consumes a vast amount of electricity in order to run. For more on paper pulp creation please visit Paper On The Web

• Forest residues, which includes wood from forest thinning operations that reduce forest fire risk, biomass not harvested or removed from logging sites in commercial hardwood and softwood stands as well as material resulting from forest management operations such as pre-commercial thinnings and removal of dead and dying trees.

• Agricultural or Crop Residues are the leftovers of harvesting. They can be collected with conventional harvesting equipment while harvesting the primary crop or afterwards into pellets, chips, stacks or bales [3]. Agriculture crop residues include corn stover (stalks and leaves), wheat straw, rice straw and processing residues such as nut hulls. With approximately 80 million acres of corn planted annually, corn stover is expected to become a major biomass resource for bioenergy applications [6]. In some areas, especially dry climates, the residues must be left to replenish the soil with nutrients for the next season and can not be completely utilized [3]. The soil can not take out all the nutrients from the residues, which translates to rotting and wasted energy sitting on top of the fields.

Animal waste, such as cattle, chicken and pig manure, can be converted to gas or burned directly for heat and power generation. In the developing world, dung cakes are used as a fuel for cooking [3]. Furthermore, most animal wastes contain high levels of methane. Thus, this method is very unsafe, as the levels of harmful chemicals given off by the biomass is hazardous to the health of users, causing 1.6 million deaths annually in the developing nations [3]. Since, animal wastes farms and animal processing operations create large amounts of animal wastes that constitute a complex source of organic materials with environmental consequences, utilizing the manure to produce energy properly lowers the environmental and health impacts. These wastes can be used to make many products and generate electricity through methane recovery methods and anaerobic digestion [4].

Urban wood waste. According to a fact sheet supplied by the California Integrated Waste Management Board, wood waste is the largest source of waste from construction products [5], generating close to 4 million tons of waste in California alone. Urban wood waste generally consists of lawn and tree trimmings, whole tree trunks, wood pallets and any other construction and demolition wastes made from lumber. This rejected material can easily be collected after a construction or demolition project and turned into mulch, compost or used to fuel bioenergy plants [5].

Municipal Solid Waste. Residential, commercial, and institutional post-consumer wastes contain a significant proportion of plant derived organic material that constitute a renewable energy resource. Waste paper, cardboard, wood waste and yard wastes are examples of biomass resources in municipal wastes. The International Energy Agency (IEA) is conducting research on municipal wastes and their use in creating bioenergy. The study will be conducted through the end of 2006. For more information, please see IEA Website.

Landfill gas. The natural byproduct of bacterial digestion of organic garbage contains vast amounts of methane which can be captured, converted and used to create energy most often through anaerobic digestion (AD). These wastes are collected and recycled through a process called anaerobic digestion and composting. Collection of landfill waste as an organic renewable resource for bioenergy is beneficial for a number of reasons, including protection of public health through treatment of waste, decreasing landfill space and inevitably decreasing odors associated with a landfill, aiding in waste management practices. Samir Khanal at Iowa State University has written a paper detailing sulfide odor control. For the text of this short write up please click here.

Energy crops are bioengineered to be fast-growing plants, trees or other herbaceous biomass which are harvested specifically for energy production use. These crops can be grown, cut and replaced quickly. For a complete list of potential plants which may be used as energy crops, please see the Handbook of Energy Crops.

Herbaceous Energy Crops

Herbaceous energy crops are perennials that are harvested annually after taking two to three years to reach full productivity. These include grasses such as switchgrass, miscanthus (Elephant grass), bamboo, sweet sorghum, tall fescue, kochia, wheatgrass, and others. These crops are generally grown for fuel production.

Woody Energy Crops

Short-rotation woody crops are fast growing hardwood trees harvested within five to eight years after planting. These include hybrid poplar (seen below), hybrid willow, silver maple, eastern cottonwood, green ash, black walnut, sweetgum, and sycamore.

Industrial Crops

Industrial crops are being developed and grown to produce specific industrial chemicals or materials. Examples include kenaf and straws for fiber, and castor for ricinoleic acid. New transgenic crops are being developed that produce the desired chemicals as part of the plant composition, requiring only extraction and purification of the product.

Agricultural Crops

These feedstocks include the currently available commodity products such as cornstarch and corn oil; soybean oil and meal; wheat starch, other vegetable oils, and any newly developed component of future commodity crops. They generally yield sugars, oils, and extractives, although they can also be used to produce plastics and other chemicals and products.

Aquatic Crops

A wide variety of aquatic biomass resources exist such as algae, giant kelp, other seaweed, and marine microflora. Commercial examples include giant kelp extracts for thickeners and food additives, algal dyes, and novel biocatalysts for use in bioprocessing under extreme environments [7]

Sources Cited:

[1] Montana Greenpower (May 12, 2005).
[2] Paper On The Web (May 16, 2005).
[3] Thomas B. Johansson, ed et al. "Biomass for Energy: Supply Prospects." Renewable Energy: Sources for Fuels and Electricity. Island Press: Washingtong, D.C. 1992. p. 609.
[4] Animal Waste Management. The University of Arizona. http://ag.arizona.edu/animalwaste/awenergy.html. July 5, 2005.
[5] Quality Management Pamphlet provided by the IEA Bioenergy Sector at http://www.novaenergie.ch/iea-bioenergy-task37/Dokumente/managementpaw3.PDF or http://www.novaenergie.ch/iea-bioenergy-task37/publicationspublic.htm
[6] "Ag economist: U.S. soybean acreage down, but not out." Purdue University. http://news.uns.purdue.edu/html4ever/2005/050331.Hurt.planting.html
[7] National Renewable Energy Laboratory. www.nrel.gov.