An American University Constructed Wetland

Achieving the Green Dream

By: Sara Schwartz

What is a Constructed Wetland?Wastewater treatment system based on

ecological systems found in natural wetlandsAble to control the wetland to meet certain

treatment standards Vegetated submerged bed: water flows through

media (gravel) instead of being exposed to the air

Basic Components

Pre-treatment tank: solids settle hereCells containing plants and mediaPlants: roots act as substrate for bacteria which

digest organic matter ex. Bulrush, Cattail Media: usually gravel, acts as filter for

suspended solidsLiner: type of plastic or rubberInlet and outlet drains: help regulate water flowIndoor filters: increase clarity, decrease

particulateStorage tank

Water FlowStorage tank trickle filter (cylindrical tank with

plastic media and air, different bacteria hosted

and treats different contaminants), one of two top

cells, sand filter, third cell, 1/3 to sand filter and

2/3 back to trickle filter to repeat process

Inside: 2 different sized micron filters UV filter

sock filterpressure tankstoilets

Commonly Asked Questions

Are they reliable? What do they treat?Performs many of same functions as conventional wastewater

treatment, acts as filter and a sink for sediment and precipitates, recycles and transforms nutrients, treats total suspended solids, biochemical oxygen demand, nitrogen, metals, toxic organics

Does it smell?May have odors by inlet pipes, but overall not a problem

because water remains below the surface of the media

What about bugs?No pools of standing water exposed to air, so not a

problem

Nitrogen Removal

Commonly Asked QuestionsHow long do they take to become fully

operational?Sidwell took about 1.5 years, need more than one growing season

to reach proper plant density, and 3 to 6 months for microbial biomass to establish in media

How much effort is needed for operation and maintenance?

About one day a week for labor, monthly or weekly inspection of weirs, weekly sampling of water, control panel provides constant feedback for technicians

How long do they last?Estimated to last 15 years but systems vary What happens in the winter?System still works but transformation and removal of nitrogen may

occur at slower rate

Our WetlandLocation: front lawn

Beeghly-unused, natural slope, visible to visitors, proximity to science classes

Capacity: treat about 300 gallons a day from bathrooms (small system), requires about 300 square feet, lawn is 14,700 square feet

Would wait for extension to be built

CostsUpfront: EPA estimates $20 per ft2, AU

wetland=$6000, lots of factors including aesthetics but with other filters and piping NSI says

$64,540.88

Maintenance: about 6% of total cost, paid annually, $360, NSI says a couple thousand a year, energy costs minimal

Funding options: DDOE $986,000 in grants for LID/green infrastructure, Chesapeake Bay Trust grants, EPA grants for green infrastructure

Benefitsslow the flow of storm water and decrease sewage

overflows into D.C. rivers reduce our use of the D.C. water supply, reduced Sidwell

Friends Middle School’s use of the water supply by 93%

decrease the university’s water bill by reusing treated water for toilet flushing, take in less water and put out less water, thus decreasing those charges on our water bill

 could help us gain up to 9 LEED credits, also give us more

points for our STARS report and contribute to our status as a leading green school

 

Benefitseducational outreach possibilities for Chemistry,

Biology, Water Resources, Ecohydrology, Sustainable Cities, and more (checking nitrogen, pH, dissolved oxygen, etc.).

 research opportunities for professors such as Dr.

MacAvoy studying movement of nutrients, and the new professor specializing in water.

 noticeable feature on campus tours and therefore a

good example of how AU is working to be sustainable  the construction of a wetland would not impact the

extension of the Beeghly building

Next StepsReceive quote from Natural Systems International-said water from lab sinks would be okay, cleaning supplies

down drain more of a concern, look for mop sinks in maintenance closets

-could design it to get nitrogen out so can use for irrigation- Not easy to re-plumb toilets, maybe just use for extension

More research: better estimate of wastewater (see number of students in classes, faculty profile, how much will come from extension), effect of reduction of students in summer, see how much space available for indoor filters

Submit to Facilities Management, Office of the Architect, District Department of Health