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New York State Pollution Prevention Institute R&D Program
2015-2016 Student Competition
Project Report – Cover Page
University/College Name Stony Brook University
Team Name The Sustainable Seawolves
Team Member Names Vani Nayyar
Kristin Welch
Armend Perasevic
Emily Nocito
External Affiliation/Business Partner The Office of Sustainability; The
Sustainability Studies Program; 10 by
2020; The Stony Brook University
Environmental Club; The Long Island
Groundwater Research Institute
Project Name Constructed Wetlands: Tackling Suffolk
County’s Wastewater System
Environmental area/opportunity addressed Wastewater Treatment
Please provide a brief one paragraph summary of your project.
Due to the outdated technology of Suffolk County’s wastewater treatment system, there is a large
amount of nitrogen-rich effluent leaching from homes. Suffolk County and the rest of Long
Island depends on a federally designated sole-source aquifer for drinking water. High levels of
nutrient loading can cause the drinking water we depend on to become inconsumable by
Environmental Protection Agency standards. To address this issue, we explored the feasibility of
using constructed wetlands as a solution to treat wastewater released from local homes in Suffolk
County. After extensive research of the literature we designed a small-scale mock-up of a
constructed wetland that is being solely used as an educational tool to visually represent the
process of nitrogen filtration.
Student Team Member Signatures:
Vani Nayyar _______________________________
Kristin Welch _______________________________
Armend Perasevic _______________________________
Emily Nocito _______________________________
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Constructed Wetlands: Tackling Suffolk County’s Wastewater System
Problem Statement
In the past 30 years, Suffolk County’s federally designated sole source aquifer has
increased dramatically in organic nitrogen. This is largely due to 74% of the county’s population
relying on outdated septic tank systems, which contributes to 70% of their total nitrogen load
(Songhen, 2014). These tanks discharge nitrogen, phosphorous, and pathogenic bacteria into the
groundwater. The high levels of organic nitrogen cause declining quality of drinking water. If
nitrate and nitrite levels exceed EPA limits of 10 mg/L and 1 mg/L respectively, the 1.5 million
residents of the county would have contaminated sources of drinking water (EPA, 2016).
Additionally, these nutrients can enter Long Island rivers, estuaries, and the Long Island Sound
causing damages varying from harmful algae blooms to brown tides (Songhen, 2014).
Left unchecked, this issue could lead to large environmental and monetary damages.
Suffolk County officials are exploring alternative solutions to treat sewage--such as membrane
technology or sewering clustered communities--before it reaches the ground and surface waters
(Songhen, 2014). Of the options considered, we believe that constructed wetlands (CW) are the
most viable option for the dispersed and expansive population of Suffolk County. When
connected to septic tanks, CW act as passive biological filters which remove nitrogen,
phosphorus, and various pathogens from the septic effluent before being discharged into the
groundwater (Vymazal, 2011).
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Project Summary/Background
Numerous studies have been conducted worldwide to study the efficiency, cost
effectiveness, and design parameters of CW. After extensive literature research, we designed a
small-scale mock-up of a CW. This is being used as an educational tool to visually represent the
process of wastewater treatment. This physical scale model combined with both visual
presentation and demonstrations to the public will provide the information needed.
We opted for a hybrid model that includes an initial vertical flow system (VFS) that then
transitions into a horizontal flow system (HFS). Although these two systems can be used
separately, we chose a hybrid model to favor the microbial processes that reduce nitrogen and
also to prevent exposure through subsurface flow. The plants we suggest are selected for their
ability to cope with both Long Island’s temperate climate and its nitrogen issues (Yount &
Crossman, 1970). Although the plants themselves do not treat the wastewater, they enhance and
provide additional substrate for crucial microbial processes that promote the reduction in
nutrients, the biological oxygen demand, and total suspended solids.
CW are not a new concept for wastewater treatment. They have been researched
extensively over the past several decades alone and are continuing to gain momentum as an
alternative method to treat wastewater. Despite advances in the scientific community, the general
public lacks knowledge on this ecologically engineered and inexpensive system. This is
extremely disadvantageous for Suffolk County and the 360,000 septic tank systems and
leachpools it houses. Of these, 200,000 are degrading groundwater and marshland habitats that
act as a second line of defense during storm events (Songhem, 2014). Compared to other
alternatives, such as sewering all of Suffolk County, CW create a natural and cheaper way to
remove nitrogen from wastewater. Through our physical small scale model, we aim to bridge the
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disconnect between the scientific community and homeowners. However, ecologically
engineering a natural process for each individual home is not easily undertaken and requires
public support.
Based on our literature review and economic analysis, we believe that that this is the most
sustainable solution for Suffolk County to pursue. CW biomimic processes of wetlands which
can be operated with minimal maintenance and installed at significantly lower costs than other
systems (EPA, 2016).
Relationship to Sustainability
Sustainably handling septic effluent before it reaches the groundwater in Suffolk County
is crucial to abating potential damages that can have exponentially increasing effects and costs.
Benefits of CW include increasing endemic biodiversity in the surrounding waterways and the
lowering of nitrogen content in the wastewater emitted into the ground. Due to the passive
engineering of the CW, it decreases energy and resource consumption in comparison to other
technologies.
Averting damage to Suffolk County’s sole source aquifer alleviates the danger of
unusable groundwater. Limiting the amount of nutrients reaching surrounding waters will
improve the health of Long Island’s waterways. The
increased resiliency against storm surges through the
strengthening of coastal wetlands will also benefit all of
Long Island as well as nearby New York City (Sobata et al.,
2015). One potential tradeoff of CW would be the land that
the homeowner’s forfeit. However, this is generally a small An example of a CW for a single family home.
(WPC, 2010)
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area and can resemble a visually attractive garden.
Materials and Methods
After learning about nitrogen loading in multiple classes and its implications for the
future of Long Island, we decided to confront the issue using an educational approach. With
encouragement from our advisor, the Director of Ecosystems and Human Impact Program, we
designed and built a small-scale physical model to represent the main processes and functions in
a CW.
By using two 15 gallon aquariums, each with the dimensions of 24” X 12” X 12” (L X D
X H), it allowed viewers a cross-sectional view into the inner workings of a CW. In both
aquariums, we created basins that ran 16” along the bottom with slanted slides that extended 6”
upwards. We constructed the basins using sturdy styrofoam layers which were then painted green
in order to represent the land in a homeowner’s backyard. With the initial structure in place,
pond liner covered the styrofoam to act as an impermeable surface that would force the
wastewater to go through the CW before entering the leachpool. We designated the first tank to
be a VFS; the second, a HFS.
In the VFS, a 18.75” pipe started from the left side of the tank and ran along the bottom
to represent the entering of wastewater from the septic tank. On the right hand side, a small 3.25”
pipe exited the structure 2” below the top. Also along the right hand side was a 15” baffle that
was placed 2” above the bottom pipe. This barrier forces the wastewater to flow in a meandering
path which allows for a longer hydraulic retention time (Vymazal, 2005). In between these
structures, we added a height of 0.77” of coarse white gravel to the bottom followed by 3.9” of
fine gravel which the wastewater would run through. The 0.77” of substrate included soil for the
artificial plants to be placed in. These three different substrates are normally found within
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functioning CW to provide additional nutrient removal based on their hydraulic conductivity
(Brix & Arias, 2005). The artificial plants in the VFS represent Common Reeds which were
spread apart in an alternating sequence of two and four inches.
In the HFS, a 3.25” pipe was placed 2” below the top left corner to show the reception of
the VFS wastewater. On the bottom right corner, a 4.75” pipe exited the aquarium along the
bottom of the basin, representing the release of the treated wastewater into the leachpool. The
same measurements for the different layers of substrate were used for the HFS. On the top layer
of the HFS, artificial plants represented Scirpus, Cattails, and Swamp Asters, each 4” apart.
Construction design for VFS.
Construction design for HFS.
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To choose appropriate plants for our model, we followed the guideline as written by
Chris Tanner’s paper, Plants for constructed wetland treatment systems - A comparison of the
growth and nutrient uptake of eight emergent species. The general requirements for suitable
plant choice in CW are as follows: (1) Ecological acceptability, (2) Tolerance of local climatic
conditions, pests & disease, (3) Tolerance of pollutants and hypertrophic waterlogged conditions,
(4) High pollutant removal capacity (Tanner, 1996).
In the vertical CW, we opted to use the Common Reed (Phragmites). These reeds assist
in nitrogen removal, but also counteract clogging of the filter. Because the reeds are semi-
emergent plants, it will also insulate the filter in the winter (Brix & Arias, 2005).
In the horizontal portion of our model, we chose to use semi-emergent plants due to their
ability to anchor anywhere (Yount & Crossman, 1970). Scirpus, also known as bulrushes, are
native to North America and are able to grow in surface water, resistant to temperature change,
and are adept nitrogen fixers (Kana & Tjepkema, 1978). Cattails (Typha) were also chosen
because they are are endemic to Long Island and can be placed in both the horizontal and vertical
portions of the model. This species take up not only nitrogen, but phosphorus as well and has
been found to decrease biochemical oxygen demand (Coon et al. 2000). Swamp Aster
(Symphyotrichum), is native to Suffolk County and has a high nitrogen removal rate (Brix &
Arias, 2005).
Determining the social cost of nitrogen involved several assumptions, and some
calculations to fit our own scope. First, there are about 360,000 homes in Suffolk County, with
an average of 4 residents (US Census, 2015). Average nitrogen excretion per capita, depending
on low and high levels for households, is 48 kg/year and 64 kg/year, respectively (Birch et al,
2011). We also compiled nitrogen impacts by dollar value based on locations within Suffolk
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County to be 18.93 $/kg/N, and 31.97 $/kg/N, for low and high levels respectively. For example,
a home near the Peconic Estuary can damage surrounding bodies of water many times faster
simply because of their location.
The finished model was our biggest milestone because it allowed us to bring the concept
of CW to the public through a physical model that utilized visualization. Our comprehensive
literature review that spanned several months informed our model and our course of action.
While two members mostly worked on the physical model, and two members focused on
the essay, we equally contributed in the literature research needed for all steps, including the
poster and presentation which will be presented on April 22nd, 2016. Additional support from
the Professor of Eco-based Literature assisted us through the essay portion, and a senior
linguistics major helped with syntax and grammar.
Results, Evaluation and Demonstration
Our educational model visually represents how a CW would look and its interaction with
the wastewater flowing out of a septic tank. However, the model is only one aspect of our
overarching goal of education. In order to properly examine the feasibility of a CW for a single
household, we relied on extensive literature research into the costs, alternatives and efficiency of
nitrogen removal.
By building a physical scale model that incorporates both HFS and VFS, our goal was to
portray maximum nitrogen removal. On its own, a VFS can remove 43% of the total nitrogen
(Brix & Arias, 2005). With a hybrid CW, it will increase the nitrogen removal to roughly 80% by
favoring nitrification and denitrification processes within the system (Vymazal, 2011). Although
our CW model specifically targets nitrogen removal, the design can be altered to fit the nutrient
removal needs by changing substrates and plant choices.
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Comparison of different methods of treatment shows the clear benefit of CW as an
efficient and feasible method for reducing nitrogen. For example, Mastic-Shirley is a
neighboring district within Suffolk County with a proposal to sewer their homes and businesses
at an initial capital cost of over $315 million (Suffolk Sewer Study, 2016). Across 12 different
`districts, we can see initial capital costs reaching well over $5 billion to sewer all of Suffolk
County with a nitrogen reduction of 70%. This value is not including the very large maintenance
and annual fees seen in sewage treatment plants (Suffolk Sewer Study, 2016). However, our
literature research into the economic feasibility of CW yielded an average cost per home of
$2,280.97 with a nitrogen reduction of 69% (EPA, 2000). With an estimation of 360,000 homes
in the county, that gives us almost $821 million as the initial cost which is much lower than the
cost of sewering Suffolk County. CW also have little to no maintenance costs after their
installation, further reducing their cost.
The abatement of nitrogen has a large external value that was used in our comparison and
feasibility. As mentioned in our methods, nitrogen footprint per household and nitrogen cost per
kilogram were calculated. After 20 years of all of Suffolk County using a CW in their home at a
69% nitrogen removal, there is a potential to abate well over $10.164 billion in damages (Sobata
et al., 2015). To compare current potential technology economically, the 20 year cost of sewering
the county would be $59.183 billion. Over the same timeframe, a CW would cost $3.175 billion
using an estimated high end maintenance cost. The overall benefit of using CW is many times
greater than the cost, while sewering yields an economic loss that outweighs the benefits.
In an attempt to estimate the potential nitrogen removed through CW in Suffolk County,
it was assumed that a 69% nitrogen reduction rate could result in the annual removal of between
11,923,200 and 15,897,600 kilograms of nitrogen (EPA, 2000).
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Although our educational model is for the purpose of outreach, it can easily be scaled to
fit the needs of the households across Suffolk County. When considering the space needed for an
efficient CW, it is suggested that for every person living in the household, the surface area of the
CW is 3.2 m2 (Brix & Arias, 2005). The surface area needed can be adjusted based on the
number of people living in a household. A household of five people, for example, would result in
16 m2 of surface area in order to properly treat the wastewater flowing out of the septic tank
(Brix & Arias, 2005). Despite the colder climate found in Suffolk County, CW are still a viable
option when they are designed with a layer of insulation to prevent freezing. This insulation layer
will allow the system to operate efficiently throughout the winter months in order to continue on-
site treatment (Wallace, 2005).
20 Year Cost Comparison of Current Technology
Comparison across three different treatment possibilities for Suffolk County effluent [Sobata et
al. (2015), Birch et al. (2011), Van Grisen et al. (2013), Dodds et al. (2009), Compton et al.
(2011), Kussiima and Powers (2010)]
Conclusions
The results of our economic analysis leads us to believe that CW are the clear choice
amongst the current available technologies. We have found that they have the potential to have a
social benefit of over $6 billion within the next two decades if implemented county wide. They
have proven to be less energy and labor intensive as well as more efficient at the removal of
Technology 20 Year Cost to
Suffolk County
Nitrogen
Removal
20 Year Social Cost of
Abatement
(High Estimate)
Cost per Kg/N
Sewage $59,183,120,000 70% $10,311,840,000 $183 - $245
Conventional
Technology
$6,387,465,600 61% $8,986,032,000 $22 - $25
Constructed Wetlands $3,175,259,400 69% $10,164,528,000 $10 - $13
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organic nitrogen.
Although artificial and constructed wetlands have been previously utilized in other
environments, it is our goal to implement them on a hyperlocal level. Implementing CW is a
proven sustainable method to naturally reduce nutrient loading from ground and surface water.
We learned education is key to the implementation of such a system. By providing the
comparison of alternative systems to CW, we hope to show homeowners that the low cost and
high nitrogen removal of CW are the best choice for households seeking alternative treatment
options.
The system we designed was based on multiple experiments and studies that researched
the effectiveness for CW to function in a typical Suffolk County lot. By attaching a hybrid CW
as an intermediary step between septic tanks and leachpools, we can reduce organic nitrogen
loads by more than 80% (Vymazal, 2011).
To better understand the receptivity of Suffolk County homeowners, extensive surveys
can be disseminated to the surrounding neighborhoods. These surveys can gauge interest and
provide feedback or concerns about our alternative treatment system.
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References
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Brix, H., & Arias, C.A. (2005). The Use of Vertical Flow Constructed Wetlands for On-Site
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