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Arcata Marsh treatment wetlands

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Overview[edit]

The Arcata Treatment Wetlands are an important phase of Secondary Treatment at the Arcata Waste Water Treatment Facility. These wetlands are perform a unique filtration process that allows the Arcata Wastewater Treatment Plant to release treated waste water into Humboldt Bay. Wastewater flows from the Oxidation ponds to the Treatment Wetlands for filtration and continues onwards to Chlorination and the Arcata Enhancement Marshes as seen in Figure 2. Arcata's Treatment Wetlands serve as an effective means of treating wastewater by removing harmful constituents.

Figure 1:An Engineering Student by the Treatment Wetlands
Figure 2: Arcata Wastewater Treatment Plant Flow Diagram

Why Treatment Wetlands[edit]

"Wetlands are among the most biologically productive ecosystems on the earth"[1], state Kadlec and Knight, authors of Treatment Wetlands. Treatment Wetlands are a cost effective way to purify waste water. Nature does most of the work, which cuts down on electricity use, which in turn cuts down on fossil fuel use. Also no added chemicals are required for the wetlands to work. In addition, wetlands often keep the smell of wastewater to a minimum. The downside to Treatment Wetlands is the amount of space they occupy, Arcata's occupies about 7.5 acres, part of which can be seen in Figure 1.

How Treatment Wetlands Work[edit]

The Arcata Wastewater Treatment Wetlands act as a biological filter for wastewater. The Arcata wetlands cover approximately 7.5 acres and are on average 2 feet deep throughout [2]. The primary function of the wetlands is to remove suspended solids, nutrients, metals, and organic compounds from the wastewater[3] by means of aquatic vegetation.

Treatment Wetlands remove constituents from the wastewater that were added in the Oxidation Ponds; this is the phase previous to Treatment Wetlands, this is noticeable in Figure 2. In the oxidation ponds algae powered by the sun creates O2 which is then absorbed by bacteria as they consume small organic matter in the wastewater. The resultant wastewater that flows into the Treatment Wetlands is high in suspended solids that need to be removed before the treatment process is complete.

The surface of the Treatment Wetlands are covered with aquatic plants, like Scirpus Acutus[1] as seen in Figure 3, that block light penetration to the water.

  • Dense vegetation on the surface of of treatment wetlands blocks sunlight which kills aerobic algae that have grown in the Oxidation Ponds. The algae then settle out to the bottom.
  • The roots of aquatic plants help to absorb harmful nutrients, metals, and organic compounds. This can be seen in Figure 4.
  • Water flows slowly through the Treatment Wetlands in about 2 days and then continues its journey to the chlorination basin.
Figure 3(Scirpus Acutus)A plant that occupies a majority of the Wetlands
Figure 4:Cross-section view of Treatment Wetlands, the roots assist in the absorption of nutrients, metals, and organic compounds

Constituents in Wastewater that Treatment Wetlands Remove[edit]

Suspended Solids[edit]

  • Any particulate suspended in water (TurbidityW) can be measured as total suspended solids using gravimetric techniques. Composed of any mix of nutrients, metals, and organic compounds. Wetlands are designed to optimize removal of suspended solids[4] by creating a stagnant environment filled with aquatic life. Stagnant water and dense vegetation cause suspended solids to either settle out of the water or absorption into plant tissues.

Nutrients[edit]

  • Phosphorus, nitrogen, and other nutrients that are in high concentrations can be detrimental to the health of many organisms including humans. For example, high concentrations of nitrate in drinking water supplies can cause methemoglobinemia, or "blue baby" syndrome, in infants[5]. The plants in the wetlands uptake these nutrients into their tissues, during their growing season, thus removing them from the water[6].

Metals[edit]

  • Trace metals can exist in wastewater in concentrations high enough to be toxic to fish, birds, humans and many other creatures. Metals like cadmium, copper, nickel, lead and zinc can be effectively removed by treatment wetlands. The metals can either settle into the bottom of the wetland, absorb into the plants, and/or gather on the outside of plant masses[7].

Organic Compounds[edit]

  • Sometimes wastewater contains man made organic chemicals that are a product of industry or household use. These chemicals are often harmful to humans in relatively small amounts. Treatment Wetlands can effectively assist in the removal of these by microbes or soil absorption[8].

The Pros and Cons of Treatment Wetlands[edit]

Pros[edit]

  • Wetlands are easy to maintain
  • The initial cost of constructing them can be less than the initial cost of alternate methods of secondary wastewater treatment, like activated sludge systems.
  • Wetlands cleanse the water through natural means without the use of chemicals

Cons[edit]

  • Wetlands occupy large spaces, Arcata's Treatment Wetlands occupy 7.5 acres.
  • Because they occupy large spaces they are generally not suitable for urban environments

The Next Phase[edit]

After the wastewater completes its two day journey it continues onward to the chlorination basin as seen in the diagram in Figure 2. The wastewater is then chlorinated and sent to the enhancement marshes and eventually into Humboldt Bay.


Treatment Wetlands in the News[edit]

Treatment Wetlands are being implemented across the world:

  • [2] Environmental Health Perspectives
  • [3] USA Today


References[edit]

  1. Kadlec 1996
  2. FOAM 2008
  3. DeBusk 1999
  4. DeBusk 1999
  5. DeBusk 1999
  6. DeBusk 1999
  7. DeBusk 1999
  8. DeBusk 1999
This Book can be found online at

http://books.google.com/books?hl=en&id=Y1XFb94MioUC&dq=treatment+wetlands&printsec=frontcover&source=web&ots=I5UWj8m-1l&sig=bWurAuyx9MOVxmkTziKG9jkLyLc#PPA3,M1


  • This page originally created by Myles Danforth
  • Photos courtesy of Dustin Poppendieck
  • Diagram courtesy of Myles Danforth