Natural processes have always cleansed
water as it flowed through rivers, lakes, streams,
and wetlands. In the last several decades,
systems have been constructed to use some of
these processes for water quality improvement.
Constructed wetlands are now used to improve
the quality of point and nonpoint sources of
water pollution, including stormwater runoff,
domestic wastewater, agricultural wastewater,
and coal mine drainage. Constructed wetlands
are also being used to treat petroleum refinery
wastes, compost and landfill leachates, fish
pond discharges, and pretreated industrial
wastewaters, such as those from pulp and paper
mills, textile mills, and seafood processing. For
some wastewaters, constructed wetlands are the
sole treatment; for others, they are one component
in a sequence of treatment processes