Flotation thickening In a dissolved air flotation (DAF) sludge thickening process,
air is introduced into liquid sludge that is being held at an elevated pressure.
When the sludge is depressurized, the dissolved air is released as finely divided
air bubbles carrying the solids to the top, where they are compacted and removed.
Flotation-filtration cell A package treatment plant which consists of both
dissolved air flotation and filtration unit processes.
Fluidized bed incinerator In the fluidized bed system, dewatered sludge or small
solid waste is fed into a bed of hot sand fluidized by circulating air. There is rapid
drying and combustion of the sludge or solid waste. Ash is carried out of the
incinerator by the combustion gases and is separated by a wet scrubber system or
equivalent.
Fluorinated gases Powerful synthetic greenhouse gases such as
hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride that are emitted
from a variety of industrial processes. Fluorinated gases are sometimes used as
substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons) and are often used in coolants,
foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants.
These gases are emitted in small quantities compared to carbon dioxide (CO 2 ),
methane (CH 4 ), or nitrous oxide (N 2 O), but because they are potent greenhouse
gases, they are sometimes referred to as high global warming potential gases
(high GWP gases).
Fluorocarbons Carbon-fluorine compounds that often contain other elements such
as hydrogen, chlorine, or bromine. Common fluorocarbons include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons
(HFCs), and perfluorocarbons (PFCs).
Forage (a) The food supply of an animal; (b) an action (of a person or animal)
searching widely for food or provisions.
Force main A pipe that carries wastewater under pressure from the discharge side
of a pump to a point of gravity flow downstream.
Forcing mechanism A process that alters the energy balance of the climate system,
i.e., changes the relative balance between incoming solar radiation and outgoing
infrared radiation from Earth. Such mechanisms include changes in solar irradiance, volcanic eruptions, and enhancement of the natural greenhouse effect by
emissions of greenhouse gases.
Fossil fuel A general term for organic materials formed from decayed plants and
animals that have been converted to crude oil, coal, natural gas, or heavy oils by
exposure to heat and pressure in the Earth’s crust over hundreds of millions of
years.
Freeboard The vertical distance from the normal water surface to the top of the
confining wall.
Fuel switching In general, this is substituting one type of fuel for another. In the
climate-change discussion, it is implicit that the substituted fuel produces lower
carbon emissions per unit energy produced than the original fuel, e.g., natural gas
for coal.
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air is introduced into liquid sludge that is being held at an elevated pressure.
When the sludge is depressurized, the dissolved air is released as finely divided
air bubbles carrying the solids to the top, where they are compacted and removed.
Flotation-filtration cell A package treatment plant which consists of both
dissolved air flotation and filtration unit processes.
Fluidized bed incinerator In the fluidized bed system, dewatered sludge or small
solid waste is fed into a bed of hot sand fluidized by circulating air. There is rapid
drying and combustion of the sludge or solid waste. Ash is carried out of the
incinerator by the combustion gases and is separated by a wet scrubber system or
equivalent.
Fluorinated gases Powerful synthetic greenhouse gases such as
hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride that are emitted
from a variety of industrial processes. Fluorinated gases are sometimes used as
substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons) and are often used in coolants,
foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants.
These gases are emitted in small quantities compared to carbon dioxide (CO 2 ),
methane (CH 4 ), or nitrous oxide (N 2 O), but because they are potent greenhouse
gases, they are sometimes referred to as high global warming potential gases
(high GWP gases).
Fluorocarbons Carbon-fluorine compounds that often contain other elements such
as hydrogen, chlorine, or bromine. Common fluorocarbons include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons
(HFCs), and perfluorocarbons (PFCs).
Forage (a) The food supply of an animal; (b) an action (of a person or animal)
searching widely for food or provisions.
Force main A pipe that carries wastewater under pressure from the discharge side
of a pump to a point of gravity flow downstream.
Forcing mechanism A process that alters the energy balance of the climate system,
i.e., changes the relative balance between incoming solar radiation and outgoing
infrared radiation from Earth. Such mechanisms include changes in solar irradiance, volcanic eruptions, and enhancement of the natural greenhouse effect by
emissions of greenhouse gases.
Fossil fuel A general term for organic materials formed from decayed plants and
animals that have been converted to crude oil, coal, natural gas, or heavy oils by
exposure to heat and pressure in the Earth’s crust over hundreds of millions of
years.
Freeboard The vertical distance from the normal water surface to the top of the
confining wall.
Fuel switching In general, this is substituting one type of fuel for another. In the
climate-change discussion, it is implicit that the substituted fuel produces lower
carbon emissions per unit energy produced than the original fuel, e.g., natural gas
for coal.
12 Glossary of Natural Resources and Environmental Pollution Control
451