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Plant Roots and Discarded Materials Purify Wastewater

Bob Cameron (photo by Steve Williams)With global freshwater supplies depleting rapidly, a system designed by Penn State horticulturalists may make wastewater usable for growing vegetables, flushing toilets, cooling buildings, and other applications.

Mimicking wetland processes, the system purifies dirty water by enmeshing plant roots in discarded materials inside upright pipes. “The treated water has very low levels of suspended solids and no detectable levels of E. coli,” says doctoral student Robert D. Cameron.

Designed by Cameron and associate professor Robert D. Berghage, the system reduces nitrate levels from washing machine wastewater by 90 percent and boron by 92 percent. Other pollutants are similarly reduced, all within three days.

Two plastic corrugated pipes filled with layers of gravel, composted manure, peat moss, tire crumbs, potting soil, and crushed limestone stand in a basin planted with papyrus and horsetail reed. Holes drilled in the pipes are planted with tomatoes, peppers, basil, and orchids; then wastewater is pumped in.

“As the dirty water trickles down the pipes, the tight mesh created by the soil, gravel, and roots filters out pollutants,” explains Cameron. Bacterial colonies among the roots consume dissolved organic matter, while periodic replacement of plants removes trapped pollutants not metabolized. Adding iron scraps or clay will trap phosphorus.

For more information read the Penn State Live release.