Converting sludge into earth

As an alternative to waste treatment plants, more man-made wetlands are being used to sanitize sludge without pollution or high energy costs.

Here's why they're so effective: Who would have thought that an efficient and environmentally friendly wastewater treatment plant actually grows in the ground? With the cost of maintaining filter and sand bed methods of treatment on the rise, man-made wetlands are becoming a popular solution to waste management needs.

This natural treatment process, which originated in Europe in the 1970s, is formally known as phytoremediation. It all begins when waste from sewage system, landfills, or chemical plants ? collectively called "sludge" ? is poured onto beds of reeds or other plants that have natural decontaminating and water-extracting properties.

Every month or so, two or three new layers of sludge are applied to these reed or plant beds. Although the plant type used in these wetlands must be suitably adaptive to the region, three varieties are the most common. The first is phragmites communis, or the common reed, which excels at dewatering. The second is phalaris arundinacea, or canarygrass reed, which can be used to treat water that is not critically contaminated and improve its quality to drinkable levels. On the other hand, it can also handle heavy-duty metal ions found in landfill leachate. It is often used in combination with peat moss, which with its optimal surface area, is perfect for waste that requires intense treatment. Cattails, natural wetland dwellers, are also being considered for future treatment use.

All of these plants work in roughly the same fashion. Reed beds, which do not have to be habitually cleared away like sand beds, are resilient, and they can adapt after a heavy loading if constructed properly.

All year round, the roots, which grow out of the plants' sides, clear away channels for water to drain back to the treatment plant. But this only accounts for some of the water. Seventy-five percent of the sludge, consisting of 98% water, evaporates with the help of the reed plant, usually more quickly in warm weather. A soil-like compound is left behind and consumed by bacteria both under ground (anaerobic) and above the surface (aerobic).

The proficiency of phytoremediation can be seen in statistics. In one square foot, the aerobic bacteria of a reed bed digest 25-75 gallons of sludge per year. Over several years, the amount of sludge that creates 10 tons of solids in a filter process only creates three in a wetland. No swamp monsters breed here: only 2-5% percent of the original sludge volume will remain once the process is complete, and 20% - 70% of the harmful solids are reduced. Some wastes only require 24 hours of treatment time.

Finally, wetland treatment sites cost as low as $10 per square foot ? only 25% of the price of traditional treatment plants.

Best of all, Mother Nature approves this process. It does not use any chemicals during treatment, nor is it dependent on fossil fuels or electricity. It relies only on solar power, in the sense that the sun sustains the principle machinery: the plants.

Wastes in the wetlands secrete no foul odors since the bacteria produces odorless byproducts, like carbon dioxide and oxygen. It also neutralizes the sludge digested by the anaerobic bacteria before it is exposed to the open air.

There are currently over 60 wetland treatment plants in the United States ? from the deserts of Arizona to the farmlands of New England.