Arcata Wastewater Treatment Plant Uses Constructed Wetlands

Published on March 31st, 2009 | by

The Arcata Wastewater Treatment Plant is one of the first and longest-running constructed wetland systems used to treat municipal wastewater.  Known by locals as the Marsh, the city of Arcata, California’s wastewater treatment facility is comprised of wetland marshes and a wildlife sanctuary.  The Marsh is an example of this unique community’s commitment to environmental politics and appropriate technology.  It facilitates multiple usage of land that not only treats this small urban city’s wastewater, but the Marsh provides wildlife habitat, research, recreation, and educational opportunities for the community.

Photo by humboldt state universityThe Arcata Marsh is used to treat wastewater.
The Arcata Marsh is used to treat wastewater.

Prior to becoming a wildlife sanctuary and marsh used in wastewater treatment, the land south of the city was an old landfill, decaying lumber deck, and pastureland:

Since the creation of the Arcata Marsh and Wildlife Sanctuary, the landscape has changed. Plants have reclaimed the previous dumping sites, and prior “wildlife” that consisted of rats, house cats, and seagulls has been adopted by close to 200 species of birds, as well as many other animals. The secondary treated water now flows through the chain of constructed treatment wetlands and enhancement marshes, and after two months it is piped into the bay, often cleaner and clearer than the bay water itself (Eisenberg 1990).

The process used at the Arcata Wastewater Treatment Plant, Marsh, and Wildlife Sanctuary is as follows:
Image by humboldt state universityArcata wastewater treatment stages

Arcata wastewater treatment stages
  1. Primary Treatment: Headworks remove sediment and other inorganic material by using bar screens and grit separators. Next, the wastewater flows through a clarifier that is used to settle out suspended solids.  Lastly, the solids are sent to a digester where they are turned into compost used in city parks and methane used in the digestion process.
  2. Secondary Treatment: Effluent from the primary clarifier is pumped to the oxidation ponds, where microorganisms naturally remove up to 50% of the biochemical oxygen demand (BOD).  Effluents then proceed to four treatment wetlands on six acres of shaded wetland.  Microorganisms living on the roots of native plants continue to reduce the BOD.
  3. Tertiary Treatment: Some of the water from the four treatment wetlands is chlorinated and dechlorinated before going to the enhancement marshes.  More BODs are removed in the enhancement marshes, and these marshes are open for public recreation.  The enhancement marshes also reduce nitrogen and phosphorous content.  The water is then either discharged into Humboldt Bay or used in the ehancement marshes to continue the cycle.

This unique use of wetland marshes to treat wastewater may not be practical for major metropolitan areas, but it certainly makes sense for Arcata:

Arcata’s treatment system occupies 307 acres (City of Arcata, 2008), roughly the same area as the Los Angeles Hyperion Treatment Plant. An activated sludge treatment plant, Hyperion utilizes energy intensive processes to treat waste such as the aeration of effluent with pure oxygen gas. The Arcata Wastewater Treatment Plant is a constructed wetland that utilizes passive, biological processes to treat effluent. Although non-energy-intensive, these processes do require a large area to function properly. The Hyperion Plant serves a population of 4,000,000 with an average flow of 450 MGD (City of Los Angeles, 2008), and the Arcata Wastewater Treatment Plant serves a population of 17,000 with an average flow of 2.3 MGD.

It is important to note a marsh wastewater system does not require overhauling a city’s infrastructure. Much of Arcata’s sewer system dates from the early 1900s.

The Arcata Marsh and Wildlife Sanctuary includes an interpretive center staffed by a naturalist.  From Japanese Buddhist nuns to local elementary school students, the Marsh has educated and enriched many people’s lives.  150,000 people visit the Arcata Marsh each year.

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