Engineers design wetlands to treat water

By JEFF SIM

SANTA FE, N.M., Oct. 22, 2000 (AP) - Like rain forests and coral reefs, wetlands are complex, vital ecosystems.

Home to thousands of species of plants, wildlife and microbes, they are, in essence, biological dynamos. They also provide a natural filtering process for water runoff, removing pollutants before they reach rivers and water tables.

These ecosystems - with their cattails, reeds, algae, reptiles, fish, herons, mallards - also can work as a model for a natural solution to a pervasive 21st century environmental problem: wastewater.

Throughout the United States, there are about 600 manmade wetlands actively treating wastewater generated by farms, cities, industries and storm run-off, according to the Environmental Protection Agency.

One company, Santa Fe-based Natural Systems International, has designed more than 350 wetlands to treat wastewater for small communities, businesses and schools in the United States, Canada and Mexico.

"It's a very appropriate technology," said John Juston, environmental engineer for DB Environmental Laboratories Inc. in Rockledge, Fla., who is working on stormwater wetlands in the Everglades.

"The place where they fit into the wastewater industry is in small communities, trailer parks, cul-de-sacs - places where it's difficult to tie into the pipes that lead into a traditional wastewater treatment plant," he said.

Since 1992, the city of Ouray, Colo., has used a Natural Systems International design that combines lagoons and a wetlands to treat the community's wastewater.

"It's an excellent system," said Ed Witherspoon, Ouray's public works supervisor, who oversees the two-acre treatment facility a mile north of the town.

"A lot of people don't know it's a wastewater plant because our cattails hide everything. The other day some people came out here and started setting up for a picnic because they didn't know what it was," he said.

Every day, more than 3 billion gallons of water wash down American homes, businesses and industrial drains, according to an EPA estimate.

That averages out to approximately 120 gallons of wastewater per person in the country - every day.

Mike Ogden, chief engineer at Natural Systems International, said constructed wetlands offer a safer alternative to conventional wastewater treatment plants, which use hazardous chemicals and are often surrounded by chain link fences and barbed wire.

"To disinfect in a modern wastewater treatment system (you) chlorinate the water. Everybody understands the value of chlorination: It kills most of the bacteria," he said.

But Ogden says that poses a problem.

"You leave residual chlorine in the water as a result of that process. And to get rid of the chlorine, because it's detrimental to the Rio Grande, you de-chlorinate using sulfur dioxide. And both are highly toxic chemicals."

Ogden, an engineer who started his company in 1989, said his wetlands follow EPA guidelines and are based on the natural processes occurring in wetlands and marshes.

Over the last 20 years, about 200 companies across the United States have been involved in the design and implementation of a variety of natural biological systems - including wetlands - to help purify water in a controlled manner, according to David Pask, an engineering scientist with National Small Flows Clearinghouse, an organization funded by the EPA.

Pask agreed that the use of chlorine and other chemicals as disinfectants to treat wastewater in municipal systems does have risks - hence the need for fences.

"There are exposed liquids in a conventional plant that you can fall into it," he said. "Children can get hurt."

However, Pask said the trend in conventional municipal treatment is to use ultraviolet light and less chlorine as the final step in disinfecting wastewater.

"Utlraviolet light is particularly sensitive to bacteria and viruses, and seems to disrupt bacteriological DNA," he said.

Constructed wetlands generally fall into two categories: those with water flowing over soil at shallow depths and those with water flowing through a porous medium, such as gravel, below the surface. Natural Solutions' wetlands fall into the second category.

A typical design might incorporate a pretreatment septic tank; a wetland to remove solids and soluble organic compounds, improve oxygen content and eliminate odor, bacteria and viruses; and a tank that siphons the treated water, which can be used to irrigate a prairie.

Prairie grasses, Ogden said, eliminate the potential for nitrate contamination of ground water.

In a conventional municipal treatment plant, wastewater is treated by a process of filtering, disinfection and nitrogen removal.

Some experts see the nitrogen removal process as a serious drawback in using constructed wetlands for wastewater treatment.

"Unfortunately, many of these systems are not working as well as they claim. Many of the systems do not appear to meet treatment standards," said Walter Zachrist, assistant director of New Mexico State University's Southwest Technology Development Institute.

"Wetlands are not good at removing nitrogen," said Haywood Martin, chief of the Construction Programs Bureau for the New Mexico Environment Department, who called nitrogen a serious contaminant.

"It's an environmental pollutant and a health hazard," he said. "You want as little being discharged as possible."

Another problem with the wetlands is that "there is some evidence that they plug up fairly rapidly," said Bruce Thomson, professor of civil engineering at the University of New Mexico.

Thomson added, "My main concern about constructed wetlands is that you have very little control over the process once it's installed. There are no valves to adjust the process. If the flow increases or the strength of the waste increases you can't adjust the process."

But Ogden said his designs incorporate viable solutions to nitrogen removal and sediment buildup.

Plus, there are other benefits, he said.

"As many communities in the United States have already shown us, wastewater treatment systems incorporating wetlands provide open space, significant wildlife habitat, running, walking and biking trails," said Ogden, noting the contrast to chain link fences and concertina wire. "With wetlands, that's gone."