Earth’s surface is absorbed by water vapor, carbon dioxide, ozone, and several
other gases in the atmosphere and then reradiated back toward the Earth’s surface.
If the atmospheric concentrations of these greenhouse gases rise, the average
temperature of the lower atmosphere will gradually increase.
Greenhouse gas (GHG) Any gas that absorbs infrared radiation in the atmosphere.
Greenhouse gases include, carbon dioxide, methane, nitrous oxide, ozone, chlorofluorocarbons,
hydrochlorofluorocarbons,
hydrofluorocarbons,
perfluorocarbons, sulfur hexafluoride.
Grinding It is a unit operation for reducing the particle size of objects or debris in
the influent wastewater, also termed shredding or comminuting. These devices
may be installed with a screen directly in the wastewater flow or separately out of
the wastewater flow, with the shredded particles returned to the flow downstream
of the screen. Only those shredding and grinding devices that are installed directly
in the influent channel are termed comminuting devices.
Grit chamber It is a grit removal device that is designed to allow the settling out of
this material. Grit removal is an important process for several reasons: (1) to
prevent cementing effects at the bottom of sludge digesters and primary clarification tanks; (2) to reduce the potential for clogging of pipes and sludge hoppers;
(3) to protect moving mechanical equipment and pumps from unnecessary wear
and abrasion; (4) to reduce accumulations of materials in aeration tanks and
sludge digesters, which would result in a loss of usable volume; and (5) to reduce
accumulations at the bases of mechanical screens. There are two types of grit
chambers. The velocity controlled grit chambers limit the velocity in the rectangular channels to a maximum of 1 foot per second (fps). This velocity is low
enough to allow the grit to settle but fast enough to maintain a majority of the
organic material in suspension. The aerated grit chambers are normally sized on
the basis of both detention time and volume of air. Typically, the detention time is
in the range of 2 to 5 minutes, and the air flow is in the range of 0.04 to 0.06 cu ft./
gallon of wastewater. The constant head type of system is normally designed
using an overflow rate of 15,000 gallons per day per square foot and a 1 minute
detention time at peak day flows.
Grit removal Grit removal is accomplished by providing an enlarged channel or
chamber which causes the flow velocity to be reduced and allows the heavier grit
to settle to the bottom of the channel where it can be removed.
Grit (a) It includes sand, gravel, cinders, coffee grounds, small stones, cigarette
filter tips, and other large-sized unwanted materials in wastewater. (b) The heavy
material present in wastewater, such as sand, coffee grounds, eggshells, gravel,
and cinders.
Groundwater The supply of fresh water found beneath the Earth’s surface (usually
in aquifers) which is often accessed through wells and springs.
Habitat fragmentation A process during which larger areas of habitat are broken
into a number of smaller patches of smaller total area, isolated from each other by
a matrix of habitats unlike the original habitat.
Halocarbons Compounds containing either chlorine, bromine, or fluorine and
carbon. Such compounds can act as powerful greenhouse gases in the
454
M.-H. S. Wang and L. K. Wang
other gases in the atmosphere and then reradiated back toward the Earth’s surface.
If the atmospheric concentrations of these greenhouse gases rise, the average
temperature of the lower atmosphere will gradually increase.
Greenhouse gas (GHG) Any gas that absorbs infrared radiation in the atmosphere.
Greenhouse gases include, carbon dioxide, methane, nitrous oxide, ozone, chlorofluorocarbons,
hydrochlorofluorocarbons,
hydrofluorocarbons,
perfluorocarbons, sulfur hexafluoride.
Grinding It is a unit operation for reducing the particle size of objects or debris in
the influent wastewater, also termed shredding or comminuting. These devices
may be installed with a screen directly in the wastewater flow or separately out of
the wastewater flow, with the shredded particles returned to the flow downstream
of the screen. Only those shredding and grinding devices that are installed directly
in the influent channel are termed comminuting devices.
Grit chamber It is a grit removal device that is designed to allow the settling out of
this material. Grit removal is an important process for several reasons: (1) to
prevent cementing effects at the bottom of sludge digesters and primary clarification tanks; (2) to reduce the potential for clogging of pipes and sludge hoppers;
(3) to protect moving mechanical equipment and pumps from unnecessary wear
and abrasion; (4) to reduce accumulations of materials in aeration tanks and
sludge digesters, which would result in a loss of usable volume; and (5) to reduce
accumulations at the bases of mechanical screens. There are two types of grit
chambers. The velocity controlled grit chambers limit the velocity in the rectangular channels to a maximum of 1 foot per second (fps). This velocity is low
enough to allow the grit to settle but fast enough to maintain a majority of the
organic material in suspension. The aerated grit chambers are normally sized on
the basis of both detention time and volume of air. Typically, the detention time is
in the range of 2 to 5 minutes, and the air flow is in the range of 0.04 to 0.06 cu ft./
gallon of wastewater. The constant head type of system is normally designed
using an overflow rate of 15,000 gallons per day per square foot and a 1 minute
detention time at peak day flows.
Grit removal Grit removal is accomplished by providing an enlarged channel or
chamber which causes the flow velocity to be reduced and allows the heavier grit
to settle to the bottom of the channel where it can be removed.
Grit (a) It includes sand, gravel, cinders, coffee grounds, small stones, cigarette
filter tips, and other large-sized unwanted materials in wastewater. (b) The heavy
material present in wastewater, such as sand, coffee grounds, eggshells, gravel,
and cinders.
Groundwater The supply of fresh water found beneath the Earth’s surface (usually
in aquifers) which is often accessed through wells and springs.
Habitat fragmentation A process during which larger areas of habitat are broken
into a number of smaller patches of smaller total area, isolated from each other by
a matrix of habitats unlike the original habitat.
Halocarbons Compounds containing either chlorine, bromine, or fluorine and
carbon. Such compounds can act as powerful greenhouse gases in the
454
M.-H. S. Wang and L. K. Wang