When Ben and Jerry's needed to drastically reduce its wastewater emissions, the Vermont-based company came up with some unconventional solutions: First it purchased about 300 pigs and fed them ice cream slop - the same gooey stuff it had previously fed to the sewers. Then it started processing other liquid wastes in a "solar aquatics system" - a big greenhouse that sent wastewater through a series of tanks filled with a variety of plants, bacteria, snails and fish that absorbed, broke down or otherwise consumed the former wastes. The strategy is part of a broader trend of harnessing nature to reduce water pollution.
Several hundred water treatment facilities in the United States now rely on constructed wetlands. Some of these facilities are relatively small like the wetland built to handle the 1200 gallons of sewage per day in a formerly abandoned school in North Carolina that was too remote to be hooked up to a municipal system. The wetland was modeled after nature, using a combination of soil, plants and microbes to process the wastewaster. Every six to eight hours, wastewater is sent through sand hills for filtering; it then enters an artificial marsh, where microbes and plants store and transform pollutants. Water then passes through a second marsh wetland, where additional filtering is performed by soils along the banks after a simulated flood. Next, the water is disinfected by ultraviolet light and dispatched to a greenhouse where tropical plants take in most of the remaining nutrients. "Nature has been cleansing water for millions of years, so we figure it's got the process figured out pretty well," says the designer, Mr. Halford House of North Carolina State University.
Much larger systems are also possible, such as the 3700 acre wetland complex in Columbia, Missouri, built to handle 13 million gallons of effluent per day from the wastewater treatment plant in Columbia, Missouri. After passing through a series of ponds, filled with marsh vegetation, the effluent is dramatically cleaned before entering the Missouri River. More than 120 species of birds and waterfowl now regularly visit the conservation area built around the constructed wetlands. As a result of this project, the city found a way to get rid of (and clean) its wastewater, yielding a water source for a planned wetlands project, while in turn creating new habitat.
The experience was similar in Arcata, California, where 154 acres of a marsh and wildlife sanctuary now stand on the site of a closed landfill. Effluent from the town's water treatment plant passes through a network of marshes for cleaning. Marsh vegetation retards water flow, enhancing the settling of solids. A host of microbial species - algae, fungi, protozoa and bacteria - then go to work, removing additional substances from the wastewater and breaking them down. More than 200 bird species have been seen at the sanctuary, along with river otters and other creatures. The constructed wetlands, proponents say, show that wastewater can be a resource rather than just a disposal problem.
More than half of the wetlands in the United States have been lost to human activities and as much as 90 percent of the wetlands in states such as California and Ohio have been wiped out.