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Due to the outdated technology of Suffolk County’s wastewater treatment system, there is a large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relying on outdated septic tank systems, which contributes to 70% of their total nitrogen load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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