Constructed Wetlands for Wastewater

Conventional on-site wastewater systems (septic systems), even when functioning properly, do not adequately prevent pollutants from reaching groundwater and surface water (see EBN March 1994). A constructed wetland is an alternative that uses plants and microorganisms living in association with plant roots to remove contaminants and nutrients from wastewater, significantly reducing groundwater contamination. Although constructed wetlands can be used to treat both stormwater and wastewater, this primer will focus on the latter.

Conventional septic systems collect wastewater in a septic tank, where organic solids settle out and anaerobic bacteria begin the process of biological decomposition. From there the wastewater is piped to a drainfield and released slowly into the soil, where aerobic bacteria continue to break down the remaining organic matter and pathogens. Conventional septic systems do not remove nitrogen and phosphorus, which fertilize bodies of water, causing algae blooms that deplete oxygen and kill aquatic life (a process known as eutrophication).


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