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Exploration of the Cost-Effectiveness of Using Oysters for Nitrogen Removal From Wastewater Relative to the Cost of Constructing Incremental Waste Water Treatment Plant Capacity

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Here we discuss the first iteration of a model that examines the case for using oysters as a tool to add incremental capacity for removing nitrogen from waste water. It was presented at the 7th......

Here we discuss the first iteration of a model that examines the case for using oysters as a tool to add incremental capacity for removing nitrogen from waste water. It was presented at the 7th Annual Massachusetts Water Resources Conference. The Massachusetts Oyster Project is a non-profit active in oyster restoration. www.massoyster.org

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  • 1. The Massachusetts Oyster Project For Clean Water Restoring oysters to their natural range to improve harbor water quality Exploration of the Cost-Effectiveness of Using Oysters for Nitrogen Removal From Wastewater Relative to the Cost of Constructing Incremental Waste Water Treatment Plant Capacity
  • 2. Nitrogen Waste
    • Average person excretes 12 pounds per year.
    • It also can be in high concentrations in agricultural run-off.
    • Excessive release to the environment can lead to a build up of nutrients, called eutrophication. eutrophication can in turn encourage the overgrowth of weeds, algae, and cyanobacteria (blue-green algae) in an algal bloom.
    • The decomposition of the algae by bacteria can use up so much of the oxygen that the area effectively dies.
  • 3. Oyster Benefits
    • Filtering water in tidal estuaries
      • 30 gallons per oyster per day
      • Feeding on phytoplankton and silt
      • Improves water clarity
      • Offsetting impact from sewer overflows and other manmade pollutants
      • Capturing nitrogen, algae and bacteria
    • Serve as keystone species in the benthic environment
    Crassostrea Virginica
  • 4. Oysters Also Sequester Nitrogen
    • Oysters are 1.4% nitrogen by weight according to Shumway World Aquaculture 2003.
    • Shells are stable and last for centuries in situ.
    • Harvested shellfish remove the shells from the ecosystem- permanently shifting the nitrogen burden.
  • 5. Oysters Offer Other Advantages
    • Oysters are passive by nature as they do not migrate or travel.
    • Oysters require minimal on-site maintenance.
    • Reproducing populations of oysters become a frees self-sustaining nitrogen sequestration system.
  • 6. Oysters Are More Active in Warm Weather When The Burden Is Higher Particulate Carbon Source: MWRA
  • 7. Cost of Removal
    • Waste water treatment plants are built with a variety of goals
      • Reducing suspended solids
      • Reducing total oxygen burden
      • Reducing nitrogen is just one part of the puzzle.
    • Adding incremental treatment for additional nitrogen removal can be expensive.
  • 8. According to a 2004 study by Gannet Fleming the incremental cost per pound removed ranged up to $30.29
  • 9. To look at the cost of Nitrogen removal via oysters we built a model using certain assumptions
    • Oyster spat 1 mm in size were purchased for $0.01 each
    • Volunteer labor was available from non-profits such as the Mass Oyster Project
    • Oyster shells contain 1.4% nitrogen by weight.
    • We ignored those shells that died before one year, nitrogen in the meat, and any sequestration from reproduction of the stock
    • We also assumed that shells from oysters that died in year 2 died at a size of one alive for 365 days.
    • We left out the amortization of the cost of a $12,000 upweller as well as electricity and insurance pending actual experience.
  • 10. Our model
  • 11. Drawbacks
    • Oysters can be a tempting hazard and efforts must be made to ensure that they are not harvested- particularly if they are downstream from waste treatment plants that provide incomplete treatment.
    • Oysters are hardy and will grow in many places, but establishing reproducing colonies is challenging.
  • 12. Advantages
    • While not appropriate as a first line treatment oysters can provide a vehicle for augmenting nitrogen removal without adding bricks and mortar, which could be important in constrained locations.
    • Oysters can be placed at low cost and offer recurring benefits.
    • Since many sites have high pollution levels this will not allow harvesting creating much needed sanctuary populations.
    • With over 200 species inhabiting an oyster reef we are enhancing biodiversity, creating shelter for creatures low on the food chain such as crabs and shrimp as well as feedstock for threatened species, such as flounder.
  • 13. Conclusions
    • This preliminary analysis shows that placement of oysters may offer a cost-effective way to augment conventional waste treatment in reducing nitrogen load.
    • Further examination and refinement of the model based on experience will provide additional value.
    • There are a host of ancillary environmental benefits that may make oysters an attractive option as waste treatment facilities seek to enhance their public image.