Acetic acid: An acid with the structure of C2H4O2. Acetyl groups are bound through an ester linkage to hemicellulose chains, especially xylans, in wood and other plants. The natural moisture present in plants hydrolyzes the acetyl groups to acetic acid, particularly at elevated temperatures.

Accumulator Tank: A large, well-insulated hot water tank. Accumulators are plumbed in to take heat directly from the boiler, they then have a secondary heating coil to take heat for heat and hot water to the rest of the system. This has the effect of decoupling heat demand from heat production, allowing the boiler to operate at best efficiency and to accept interruptions to the heat supply. It also allows some lee-way in the specification of the boiler, as the accumulator is able to smooth some of the peaks and troughs in demand.

Acid: A solution that has an excess of hydrogen ions (H+).

Acid detergent fiber (ADF):  Organic matter that is not solubilized after one hour of refluxing in an acid detergent of cetyltrimethylammonium bromide in 1N sulfuric acid. ADF includes cellulose and lignin. This analytical method is commonly used in the feed and fiber industries

Acid hydrolysis: The treatment of cellulosic, starch,  or  hemicellulosic materials using acid solutions (usually mineral acids) to break down the polysaccharides to simple sugars.

Acid insoluble lignin: Lignin is mostly insoluble in mineral acids, and therefore can be analyzed gravimetrically after hydrolyzing the cellulose and hemicellulose fractions of the biomass with sulfuric acid.

Acid soluble lignin: A small fraction of the lignin in a biomass sample is solubilized during the hydrolysis process of the acid insoluble lignin method. This lignin fraction is referred to as acid soluble lignin and may be quantified by ultraviolet spectroscopy

Acre: An area of land measuring 43,560 square feet.

Adaptive Management: A dynamic approach to forest management in which the effects of treatments and decisions are continually monitored and used, along with research results, to modify management on a continuing basis to ensure that objectives are being met.

Adsorption: The adhesion, in an extremely thin layer,  of  molecules (as in gases, solutions, or liquids) to the surface of  solid  bodies or liquids with which they are in contact.

Aerobic: Able to live, grow, or take place only where free oxygen is present.

Aerobic fermentation: Fermentation processes that require the presence of oxygen.

Agricultural residue: Agricultural crop residues are the plant parts, primarily stalks and leaves, not removed from the fields with the primary food or fiber product. Examples include corn stover (stalks, leaves, husks, and cobs); wheat straw; and rice straw.

Air dry : The state of dryness at equilibrium with the water content in the surrounding atmosphere. The actual water content will depend upon the relative humidity and temperature of the surrounding atmosphere.

Alcohol: An alcohol is an organic compound with a carbon bound to a hydroxyl group. Examples are methanol (CH3OH) and ethanol (CH3CH2OH).

Aldehyde: Any of a class of highly reactive organic chemical compounds characterized by the common group CHO and used in the manufacture of resins, dyes, and organic acids.

Aldoses: Occur when the carbonyl group of a monosaccharide is an aldehyde.

Algae : Algae are primitive plants, usually aquatic, capable    of synthesizing their own food by photosynthesis. Algae is currently being investigated as a possible feedstock for producing biodiesel.

Alkali: Soluble mineral salt of alkali metals having characteristically “basic” properties.

Alkaline hydrolysis: The use of solutions of sodium hydroxide (or other alkali) in the treatment of cellulosic material (wood) to break down cellulose to simple sugars.

Alkali lignin: Lignin obtained by acidification of an alkaline extract of wood.

Alkaline metals : Potassium and sodium oxides (K2O + NaO2) that are the main chemicals in biomass solid fuels that cause slagging and fouling in combustion chambers and boilers.

Alkylation: A process for manufacturing high-octane blending components used in unleaded petrol or gasoline.

Amalgamation: the process of combining or uniting multiple entities into one form.

Amylase: Family of enzymes that act together to hydrolyze starch to individual glucose and dextran units.

Anaerobic: Living or active in an airless environment.

Anaerobic digestion: Degradation of organic matter by microbes in the absence of oxygen to produce methane and carbon dioxide.

Anaerobic process: A (part of a) process that occurs in the absence of free oxygen.

Anhydrous: A material that does not contain water, either adsorbed on its surface or as water of crystallization.

Annual: A plant that completes its life cycle in one year or less.

Annual removals: The net volume of growing stock trees removed from the inventory during a specified year by harvesting, cultural operations, such as, timber stand improvement, or land clearing.

API gravity: A measure of the lightness or heaviness of petroleum that is related to density and specific gravity. ⁰API = (141.5/specific gravity @ 60⁰F) – 131.5.

Appliance efficiency: The ratio of output energy to input energy when the combustion system is running under design conditions. Also called steady state efficiency.

Aquatic plants: The aquatic biomass resources, such as algae, giant kelp, other seaweed, and water hyacinth. Certain microalgae can produce hydrogen and oxygen while others manufacture hydrocarbons and a host of other products. Microalgae examples include Chlorella, Dunaliella, and Euglena.

Arabinan: The polymer of arabinose with a repeating unit of C5H804. Can be hydrolyzed to arabinose.

Arabinose: A five-carbon sugar - C5H1005. A product of hydrolysis of arabinan found in the hemicellulose fraction of biomass.

Archaea (formerly Archaebacteria ): A group of single-celled microorganisms. A single individual or species from this domain is called an archaeon (sometimes spelled "archeon"). They have no cell nucleus or any other organelles within their cells.

Aromatic: A chemical that has a benzene ring in its  molecular structure (benzene, toluene, xylene). Aromatic compounds have  strong, characteristic odors.

Asexual reproduction: The naturally occurring ability of some plant species to reproduce asexually through seeds, meaning the embryos develop without a male gamete. This ensures the seeds will produce plants identical to the mother plant.

Ash: Residue remaining after ignition of a sample determined by a definite prescribed procedure.

Ashing auger: An auger, operated manually or by a motor, used to remove ash from the base of a furnace or boiler setting. Also called ashing screw.

Asphaltene (asphaltenes): The brown to black powder material produced by treatment of petroleum, heavy oil, bitumen, or residuum with a low-boiling liquid hydrocarbon.

Attainment area: A geographic region where the concentration of a specific air pollutant does not exceed federal standards.

Auger:  A rotating, screw-type device that moves material through a cylinder. In alcohol production, it is used to transfer grains from storage to the grinding site and from the grinding site to the cooker.

Avoided costs: An investment guideline describing the value of a conservation or generation resource investment by the cost of more expensive resources that a utility would otherwise have to acquire.

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