Recycling Collecting and reprocessing a resource so that it can be used again. An
example is collecting aluminum cans, melting them down, and using the aluminum to make new cans or other aluminum products.
Reduction A chemical reaction involving the addition of electrons to a chemical
entity.
Refinery A refinery is a production facility composed of a group of chemical
engineering unit processes and unit operations refining certain materials or
converting raw material into products of value.
Refining waste A refining waste or refinery waste is the waste or wastewater from a
refinery.
Reflectivity The ability of a surface material to reflect sunlight including the visible,
infrared, and ultraviolet wavelengths.
Reforestation Planting of forests on lands that have previously contained forests
but that have been converted to some other use.
Relative humidity The ratio of the partial pressure of water vapor in the air to the
vapor pressure of water at the temperature of the air, which contains the water
vapor.
Relative sea level rise The increase in ocean water levels at a specific location,
taking into account both global sea level rise and local factors, such as local
subsidence and uplift. Relative sea level rise is measured with respect to a
specified vertical datum relative to the land, which may also be changing elevation over time.
Renewable energy Energy resources that are naturally replenishing such as biomass, hydro, geothermal, solar, wind, ocean thermal, wave action, and tidal
action.
Reservoir dredging It is common for cities and municipalities to source the
community’s water from open-air reservoirs. Sometimes these reservoirs will
silt-in or become contaminated with material that drains from the surrounding
area. Dredging is an efficient and effective way to continually keep these reservoirs clean.
Residence time The average time spent in a reservoir by an individual atom or
molecule. With respect to greenhouse gases, residence time refers to how long on
average a particular molecule remains in the atmosphere. For most gases other
than methane and carbon dioxide, the residence time is approximately equal to the
atmospheric lifetime.
Resilience A capability to anticipate, prepare for, respond to, and recover from
significant multihazard threats with minimum damage to social well-being, the
economy, and the environment.
Respiration The process whereby living organisms convert organic matter to CO 2 ,
releasing energy and consuming O 2 .
Retention time The time water, sludge, or solids are retained or held in a clarifier or
sedimentation tank.
Return activated sludge (RAS) (a) Settled activated sludge, returned from the
bottom of final sedimentation clarifiers, to mix with incoming raw or primary
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example is collecting aluminum cans, melting them down, and using the aluminum to make new cans or other aluminum products.
Reduction A chemical reaction involving the addition of electrons to a chemical
entity.
Refinery A refinery is a production facility composed of a group of chemical
engineering unit processes and unit operations refining certain materials or
converting raw material into products of value.
Refining waste A refining waste or refinery waste is the waste or wastewater from a
refinery.
Reflectivity The ability of a surface material to reflect sunlight including the visible,
infrared, and ultraviolet wavelengths.
Reforestation Planting of forests on lands that have previously contained forests
but that have been converted to some other use.
Relative humidity The ratio of the partial pressure of water vapor in the air to the
vapor pressure of water at the temperature of the air, which contains the water
vapor.
Relative sea level rise The increase in ocean water levels at a specific location,
taking into account both global sea level rise and local factors, such as local
subsidence and uplift. Relative sea level rise is measured with respect to a
specified vertical datum relative to the land, which may also be changing elevation over time.
Renewable energy Energy resources that are naturally replenishing such as biomass, hydro, geothermal, solar, wind, ocean thermal, wave action, and tidal
action.
Reservoir dredging It is common for cities and municipalities to source the
community’s water from open-air reservoirs. Sometimes these reservoirs will
silt-in or become contaminated with material that drains from the surrounding
area. Dredging is an efficient and effective way to continually keep these reservoirs clean.
Residence time The average time spent in a reservoir by an individual atom or
molecule. With respect to greenhouse gases, residence time refers to how long on
average a particular molecule remains in the atmosphere. For most gases other
than methane and carbon dioxide, the residence time is approximately equal to the
atmospheric lifetime.
Resilience A capability to anticipate, prepare for, respond to, and recover from
significant multihazard threats with minimum damage to social well-being, the
economy, and the environment.
Respiration The process whereby living organisms convert organic matter to CO 2 ,
releasing energy and consuming O 2 .
Retention time The time water, sludge, or solids are retained or held in a clarifier or
sedimentation tank.
Return activated sludge (RAS) (a) Settled activated sludge, returned from the
bottom of final sedimentation clarifiers, to mix with incoming raw or primary
12 Glossary of Natural Resources and Environmental Pollution Control
477