Ch 18, 21, 23 Vocabulary

primary sewage treatment
Mechanical sewage treatment in which large solids are filtered out by screens and suspended solids settle out as sludge in a sedimentation tank.
secondary sewage treatment
Step in most waste treatment systems in which aerobic bacteria decompose up to 90% of degradable, oxygen-demanding organic wastes in wastewater. This usually involves bringing sewage and bacteria together in trickling filters or in the activated sludge process.
tertiary sewage treatment
Specialized chemical and physical processes that reduce the amount of specific pollutants left in wastewater after primary and secondary sewage treatment. This type of treatment usually is expensive.
arable land
Land that can be cultivated to grow crops.
emigration
Movement of people out of a specific geographic area. See migration.
immigration
Migration of people into a country or area to take up permanent residence.
land-use planning
Process for deciding the best present and future use of each parcel of land in an area.
mass transit
Buses, trains, trolleys, and other forms of transportation that carry large numbers of people.
noise pollution
Any unwanted, disturbing, or harmful sound that impairs or interferes with hearing, causes stress, hampers concentration and work efficiency, or causes accidents.
smart growth
Form of urban planning which recognizes that urban growth will occur but uses zoning laws and an array of other tools to prevent sprawl, direct growth to certain areas, protect ecologically sensitive and important lands and waterways, and develop urban areas that are more environmentally sustainable and more enjoyable places to live.
urban area
Geographic area with a population of 2,500 or more. The number of people used in this definition may vary, with some countries setting the minimum number of people at 10,000-50,000.
urban sprawl
Growth of low-density development on the edges of cities and towns.
zoning
Regulating how various parcels of land can be used.