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Treatment Wetlands Appropriateness

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figure 1: Cattails in Arcata's Treatment Wetlands

Cost[edit]

Funding for Wastewater treatment is limited in Arcata, a small city in California with a population of 17,294[1]. Limited operational budgets made Treatment Wetlands an appealing solution to Arcata's Wastewater problems. The costs of Treatment Wetlands are largely based on the price and availability of land[2]. Otherwise, treatment wetlands are a low-cost alternative to activated sludge systems because constructed wetlands utilize natural processes as opposed to using an energy demanding process of running pumps to inject oxygen into the sludge to treat wastewater[3].

Location[edit]

Location is a deciding factor in the placement of Treatment Wetlands. Treatment Wetlands are unable to function in freezing climates[4]. Also, high levels of rainfall can increase the amount of effluent created by the Wastewater Treatment Plant. This effect is exaggerated by the surface area of the oxidation ponds. Since oxidation ponds are open to the air and take up 55 acres of the Arcata Marsh, rainwater will naturally be added to the water being treated. An increase in effluent can increase the need for a larger capacity in disinfection[5].

Plants[edit]

Plants were chosen carefully in order to account for large changes in flow rate. The changes in flow rate in Arcata, CA are caused by a seasonal change in population that nearly doubles between August and May (due to Humboldt State University's school sessions) as well as an aging sewer system part of which was built in the 1880's. The sewer system is subject to infiltration during heavy rainfall. These changes limit the selection of plants available for use in the Treatment Marsh.


There were three groups of plants that were used:

  1. Submergent plants "provide surface area for decomposers (fungi) and bacteria that nitrify and denitrify" (EPA 1993) the wastewater.
  2. Emergent, whose roots contribute to the biological filter of solids and provide shade from UV rays.
  3. Floating Plants, which are primarily used to shade and block out sunlight.

Preference was given to native plants; Hardstem Bulrush and Cattails are native plants that are present at the Wastewater Treatment Plant. The most prominent plants that are in use at the Arcata Treatment Wetlands are listed in Table 1 .


Table 1
Plants used in the Treatment Wetlands
Common Name Latin name Picture Purpose
Submergent Sago Pondweed Potamogeton pectinatus Plants provide an area for fungus and bacteria to add and remove nitrogen.
Emergent Hardstem Bullrush

(native)

scirpus acutus Roots provide a place for bacteria and fungus to add and remove nitrogen. Emergent portions provide shade to prevent the growth of algae, cool water, reduce evaporation, and add oxygen via photosynthesis[6].
Water Dropwort Oenanthe
Arcata-7133 Water Dropwort reduced.jpg
Cattail

(native)

typha
Arcata-7120 reduced.jpg
Floating Duckweed Lemna
Hydrocotyle Hydrocotyle
Arcata-7021 Hydrocotyle reduced.jpg
[7]

References[edit]

  1. California State Statistical Abstract. (January 2007).California Statistical Abstract.Retrieved May 5, 2008, from http://www.dof.ca.gov/HTML/FS_DATA/STAT-ABS/Toc_xls.htm
  2. Homer, Denise. Interview. 27 Mar. 2008.
  3. Poppendieck, Dustin. Interview. 28 Mar. 2008.
  4. Poppendieck, Dustin. Interview. 28 Mar. 2008.
  5. Couch, David. Interview. 7 March 2008.
  6. United States Environmental Protection Agency. (1993). A Natural System for Wastewater Reclamation and Resource Enhancement (EPA832-R-93-005e). Arcata, CA.
  7. Shrader, Jesse. 2008.
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