engineering community typically has not been involved in conservation,
but now engineers are collaborating with biologists, ecologists, and
other scientists to solve some of the world's water problems.
By Corinna Wu
the Purdue University Research Farms in West Lafayette, Ind., found
themselves in some deep doo-doo. A machine that automatically sprays
fertilizer over crops failed to turn itself off, dumping a huge amount
of liquid manure over the field. By the time the accident was discovered,
excess manure had begun flowing into the farms' drainage ditch, threatening
to contaminate the Wabash River downstream.
have turned into a major incident, but luckily, Purdue engineering students
had recently completed constructing a sort of wastewater treatment facility
right next to the ditch: an artificial wetland. The heavily contaminated
water was pumped into the wetland and emerged clean enough to swim in.
wetlands and most people conjure up an image of a humid swamp edged
with cypress trees, buzzing with mosquitoes, and maybe supporting an
alligator or two. But natural wetlands are found in all kinds of climates
and are variously known as swamps, bogs, fens, sloughs, or marshes,
depending on the kind of vegetation found there. Water can saturate
it just part of the year or all year round. And like Purdue, many communities
in the United States and around the world are actually building artificial
wetlands to solve wastewater treatment problems.
referred to as the kidneys of the world, wetlands clean
water by filtering out contaminants and concentrating them. Water moves
through a wetland slowly, giving plants and microorganisms a chance
to ingest and break down pollutants. Compounds containing nitrogen and
phosphorus might make water unfit to drink but are the very nutrients
that plants and microbes need to thrive. Some types of vegetation can
even take up and store heavy metalsa property that has prompted
environmental scientists to consider plants as a low-cost way to remediate
sites contaminated with industrial waste. After moving through a wetland,
the now-clean water usually makes its way to a stream or deep into the
wetlands serve the same purpose as the natural onesto treat contaminated
water. In some parts of the world, such as Africa, a wetland might be
the only such treatment available, says Thomas Crisman, director of
the Center for Wetlands at the University of Florida, Gainesville. It's
raw sewage going in. And like at the Purdue Farms, a constructed
wetland can act as a buffer zone for agricultural runoff, intercepting
fertilizers and pesticides before they trickle into the environment.
urban areas, constructed wetlands usually act as the last step in the
filtration process. We see them as a means of retrofitting old
sewage treatment plants in small municipalities, Crisman says.
They don't have the ability to upgrade their facilities, yet they're
dumping out into a local stream. And so a small town could put a wetland
at the end of their sewage treatment plant to polish it off.
town of Gilbert, Ariz., located southeast of Phoenix, wetlands don't
do any clean-up at all. About 15 years ago, Gilbert decided that it
would reuse 100 percent of its water supply and built a treatment plant
to handle the wastewater it generated. At the same time, the town decided
to funnel part of that water back into the ground through a group of
11 ponds on a 72-acre sitea wetland in the middle of the desert.
is treated before being sent to the ponds and then drains through the
sandy soil, eventually making its way to wells where it can be pumped
out again for use. About a third of the 6 to 7 million gallons of wastewater
the town processes daily makes it into the basins, says Scott Anderson,
director of the Riparian Institute, the organization that promotes and
develops Gilbert's wetland preserves. It takes only a week for the water
to completely percolate into ground, he adds, and only 5 percent is
lost to evaporationnot bad for Arizona's sunny, dry climate. Anderson
says that since the first wetland site at Neely Ranch was built in 1990,
the ponds have indeed succeeded in raising the water table.
of the basins also had an unintended effect. We were inadvertently
attracting a lot of different kinds of birds, especially migratory birds
during particular seasons, says Anderson. This happened even though
they had not planted any vegetation to encourage birds to use the ponds
as a pit stop. So Anderson and his colleagues decided to go all out
and develop the site as a riparian habitat, a waterside landscape characterized
by trees like cottonwoods and willows. Riparian areas only occupy 1
percent of Arizona's landscape but support more than 60 percent of its
wildlife. Years ago, there used to be a lot of water running through
this valley, says Anderson. But we've since dammed those
rivers, so that's taken away a lot of the riparian areas. And
more of them are in danger of disappearing as water is siphoned off.
Ranch and a newer preserve at Water Ranch have become favored places
for birdwatchers; the Audubon Society has identified 140 different species
that make appearances at the sites. Circled with paths and picnic areas,
the ponds are now part of recreational areas for the townoases
in the desert. Some of the water is diverted to a fishing lake, stocked
with trout, bass, and catfish.
says that since natural wetlands serve many purposes, constructed wetlands
are a way for engineers to achieve several goals at once. The
engineering community [traditionally] has not been involved in conservation.
Now here's the ability to engineer a system that can serve a conservation
purpose. For example, he and his colleagues are trying to identify
ways of squeezing value out of wetlands beyond their traditional benefits.
If you consider wastewater as a resource, then wastewater can
be used to create products, he says.
with the Technical University in Darmstadt, Germany, for example, he's
looking at bamboo as a potential product. A strong, flexible, fast-growing
grass, bamboo can be chipped into particle board or used as a building
material. We're trying to create a product that's part of the
maintenance of the system, he explains. That way, regular maintenance
of the wetland would yield an additional source of income, which would
be especially welcome in developing countries.
constructed wetlands offer a way to look at old problems in new ways.
As an example, Crisman cites a project that was initiated a few years
ago by students at the University of Florida. They redesigned a planned
stormwater retention basin on campus into a functional wetland, securing
all the necessary permits and getting the support of the university
and local water management authority. Called the Stormwater Ecological
Enhancement Project, it's now used as a teaching facility. We're
really trying to do those things at the interface between classical
engineering and ecology and conservation, Crisman says. Those
sort of hybrid programs are where it's going to go in the future.
the constructed wetland next to the research farms is part of the Engineering
Projects in Community Service (EPICS) program funded by the National
Science Foundation. EPICS pairs student engineering teams with community
service organizations, allowing the students to get real-world experience
as technical consultants. The constructed wetlands [project] is
atypical of the normal program because we don't have a true social service
agency that we're working for, says William Oakes, co-director
of EPICS at Purdue. In a sense, we're working for the environment.
find these experiences useful, even if they never work on another constructed
wetland for the rest of their careers. In all areas of civil engineering,
environmental impacts are becoming more and more important, says
Geoff Henggeler, a junior civil engineering student who's worked on
the constructed wetland at Purdue for about two years. I don't
think that there's a single civil engineering project that you could
be involved with that doesn't involve environmental engineering at least
to a minor degree.
projects at universities draw students from all different areas of science
and engineering. Twenty different majors are represented in the EPICS
project, Oakes says. The opportunity to collaborate with a diverse group
of people is valuable training, since wetlands engineers often rely
on the expertise of biologists, ecologists, and hydrologists to figure
out the needs of a particular site.
engineering solution, constructed wetlands serve multiple purposes.
Some of those goals can be measured in dollars, but others are harder
to assign a value. In Gilbert, what started as a municipal water project
has become a point of pride for the town. Communities here in
the valley have their own identity, says Anderson. Gilbert's
kind of identified this as their own little niche, creating these habitats,
these areas that are really unique. And it's been very successful.
And for engineering students finding their way to a career, working
on a constructed wetland project is one way to put their classroom skills
to a real-world test.
Wu is a freelance writer based in suburban Washington, D.C.
She can be reached at firstname.lastname@example.org.