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The Massachusetts Oyster Project For Clean WaterThe Massachusetts Oyster Project For Clean Water Restoring oysters to their natural Restoring oysters to their natural range to improve harbor water range to improve harbor water

qualityquality

Exploration of the Cost-Exploration of the Cost-Effectiveness of Using Oysters for Effectiveness of Using Oysters for

Nitrogen Removal From Nitrogen Removal From Wastewater Relative to the Cost Wastewater Relative to the Cost

of Constructing Incremental of Constructing Incremental Waste Water Treatment Plant Waste Water Treatment Plant

CapacityCapacity

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Nitrogen Waste Nitrogen Waste Average person excretes 12 pounds per year.Average person excretes 12 pounds per year. It also can be in high concentrations in It also can be in high concentrations in

agricultural run-off.agricultural run-off. Excessive release to the environment can lead Excessive release to the environment can lead

to a build up of nutrients, called eutrophication. to a build up of nutrients, called eutrophication. eutrophication can in turn encourage the eutrophication can in turn encourage the overgrowth of weeds, algae, and cyanobacteria overgrowth of weeds, algae, and cyanobacteria (blue-green algae) in an algal bloom.(blue-green algae) in an algal bloom.

The decomposition of the algae by bacteria can The decomposition of the algae by bacteria can use up so much of the oxygen that the area use up so much of the oxygen that the area effectively dies. effectively dies.

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Oyster BenefitsOyster Benefits Filtering water in tidal estuariesFiltering water in tidal estuaries

30 gallons per oyster per day30 gallons per oyster per day Feeding on phytoplankton and silt Feeding on phytoplankton and silt Improves water clarityImproves water clarity Offsetting impact from sewer overflows and other manmade Offsetting impact from sewer overflows and other manmade

pollutantspollutants Capturing nitrogen, algae and bacteriaCapturing nitrogen, algae and bacteria

Serve as keystone species in the benthic environmentServe as keystone species in the benthic environment

Crassostrea Virginica

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Oysters Also Sequester NitrogenOysters Also Sequester Nitrogen Oysters are 1.4% nitrogen by weight according Oysters are 1.4% nitrogen by weight according

to Shumway World Aquaculture 2003.to Shumway World Aquaculture 2003. Shells are stable and last for centuries in situ.Shells are stable and last for centuries in situ. Harvested shellfish remove the shells from the Harvested shellfish remove the shells from the

ecosystem- permanently shifting the nitrogen ecosystem- permanently shifting the nitrogen burden.burden.

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Oysters Offer Other AdvantagesOysters Offer Other Advantages Oysters are passive by nature as they do Oysters are passive by nature as they do

not migrate or travel.not migrate or travel. Oysters require minimal on-site Oysters require minimal on-site

maintenance. maintenance. Reproducing populations of oysters Reproducing populations of oysters

become a frees self-sustaining nitrogen become a frees self-sustaining nitrogen sequestration system.sequestration system.

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Oysters Are More Active in Warm Oysters Are More Active in Warm Weather When The Burden Is HigherWeather When The Burden Is Higher

Particulate Carbon

Source: MWRA

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Cost of RemovalCost of Removal Waste water treatment plants are built Waste water treatment plants are built

with a variety of goalswith a variety of goals Reducing suspended solidsReducing suspended solids Reducing total oxygen burdenReducing total oxygen burden Reducing nitrogen is just one part of the Reducing nitrogen is just one part of the

puzzle.puzzle. Adding incremental treatment for Adding incremental treatment for

additional nitrogen removal can be additional nitrogen removal can be expensive. expensive.

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According to a 2004 study by Gannet According to a 2004 study by Gannet Fleming the incremental cost per pound Fleming the incremental cost per pound

removed ranged up to $30.29removed ranged up to $30.29

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To look at the cost of Nitrogen To look at the cost of Nitrogen removal via oysters we built a model removal via oysters we built a model

using certain assumptionsusing certain assumptions Oyster spat 1 mm in size were purchased Oyster spat 1 mm in size were purchased

for $0.01 eachfor $0.01 each Volunteer labor was available from non-Volunteer labor was available from non-

profits such as the Mass Oyster Projectprofits such as the Mass Oyster Project Oyster shells contain 1.4% nitrogen by Oyster shells contain 1.4% nitrogen by

weight. weight. We ignored those shells that died before We ignored those shells that died before

one year, nitrogen in the meat, and any one year, nitrogen in the meat, and any sequestration from reproduction of the sequestration from reproduction of the stockstock

We also assumed that shells from oysters We also assumed that shells from oysters that died in year 2 died at a size of one that died in year 2 died at a size of one alive for 365 days. alive for 365 days.

We left out the amortization of the cost of We left out the amortization of the cost of a $12,000 upweller as well as electricity a $12,000 upweller as well as electricity and insurance pending actual experience. and insurance pending actual experience.

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Our model Our model

Variables to be filled

Hard Numbers

Output

Cost per pound of nitrogen removal at treatment facility $16.55 Cost for a pound of Nitrogen Removal $16.55

Cost per Oyster $0.01 Cost per Oyster $0.01 Year 1 Year 2 Year 3

Oysters Bought 1655 Oysters bought 1655

Percentage Nitrogen 1.4% Percentage surviving year one 45%Oysters Surviving Year 1 745

One Year Oyster Shell Weight 0.044Oysters dying in year 2 148.95

Two Year Oyster Shell Weight (lbs) 0.088 Shell weight (lbs) each 0.044Shell pounds 6.5

Three Year Oyster Shell Weight (lbs) 0.118 Nitrogen Percentage 1.40%Pounds of Nitrogen in Shell 0.09

Percentage Surviving Year 2 80%Oyster Survival Year 1 45% Oysters Surviving Year 2 596

Number 745 Oysters dying in year 3 179Oyster Survival Year 2 80% Shell weight (lbs) each 0.0875

Number 596 Shell Pounds 15.6Oyster Survival Year 3 70% Nitrogen Percentage 1.40%

Number 417 Pounds of Nitrogen in Shell 0.22Finalist Survivals 25%

Percentage Surviving Year 3 70%Oysters Surviving Year 3 417

Shell weight (lbs) each 0.12Increase in nitrogen removal 0.0% Shell Pounds 49.3

Nitrogen Percentage 1.40%Pounds of Nitrogen in Shell 0.7

Total Pounds of Nitrogen 1.00Increase in Efficiency 0.0%

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DrawbacksDrawbacks Oysters can be a tempting hazard and Oysters can be a tempting hazard and

efforts must be made to ensure that they efforts must be made to ensure that they are not harvested- particularly if they are are not harvested- particularly if they are downstream from waste treatment plants downstream from waste treatment plants that provide incomplete treatment.that provide incomplete treatment.

Oysters are hardy and will grow in many Oysters are hardy and will grow in many places, but establishing reproducing places, but establishing reproducing colonies is challenging.colonies is challenging.

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AdvantagesAdvantages While not appropriate as a first line treatment While not appropriate as a first line treatment

oysters can provide a vehicle for augmenting oysters can provide a vehicle for augmenting nitrogen removal without adding bricks and nitrogen removal without adding bricks and mortar, which could be important in constrained mortar, which could be important in constrained locations.locations.

Oysters can be placed at low cost and offer Oysters can be placed at low cost and offer recurring benefits.recurring benefits.

Since many sites have high pollution levels this Since many sites have high pollution levels this will not allow harvesting creating much needed will not allow harvesting creating much needed sanctuary populations. sanctuary populations.

With over 200 species inhabiting an oyster reef With over 200 species inhabiting an oyster reef we are enhancing biodiversity, creating shelter for we are enhancing biodiversity, creating shelter for creatures low on the food chain such as crabs creatures low on the food chain such as crabs and shrimp as well as feedstock for threatened and shrimp as well as feedstock for threatened species, such as flounder. species, such as flounder.

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ConclusionsConclusions This preliminary analysis shows that placement This preliminary analysis shows that placement

of oysters may offer a cost-effective way to of oysters may offer a cost-effective way to augment conventional waste treatment in augment conventional waste treatment in reducing nitrogen load.reducing nitrogen load.

Further examination and refinement of the Further examination and refinement of the model based on experience will provide model based on experience will provide additional value. additional value.

There are a host of ancillary environmental There are a host of ancillary environmental benefits that may make oysters an attractive benefits that may make oysters an attractive option as waste treatment facilities seek to option as waste treatment facilities seek to enhance their public image. enhance their public image.