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

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

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.

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

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.

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.

Oysters Are More Active in Warm Weather When The Burden Is Higher Particulate Carbon Source: MWRA

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.

According to a 2004 study by Gannet Fleming the incremental cost per pound removed ranged up to $30.29

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.

Our model

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.

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.

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.

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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

by Massachusetts Oyster Project for Clean Water on Apr 02, 2010

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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 — Presentation Transcript