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Drexel Researchers Recycle Rainwater from Urban Rooftops

March 31, 2011

March 31, 2011 A team of Drexel civil and environmental engineers are studying ways to use rainwater as a resource rather than disposing of it as waste. Rather than conveying it in pipes to treatment plants and receiving water bodies, the team suggests that rainwater runoff can be recycled for non-potable building uses, become an irrigation supply for gardens and farms and infiltrated into the ground to enhance urban ecosystems. In search of ways to control regulatory compliance costs and maintain service levels, cities such as New York and Philadelphia are paying careful attention. 

The project, led by Dr. Franco Montalto, assistant professor of civil, architectural and environmental engineering, and a team of undergraduate and graduate students, are working on a number of projects across the urban northeast and beyond. In Drexel’s backyard, the team is working with organizations such as the Partnership Community Development Corporation and Urban Tree Connection to compare the quantity and quality of runoff from vegetated, “cool” (a term referring to roofs coated with reflective paints) and conventional roof surfaces.

“During the same rain event, we expect that the vegetated roof surfaces will produce lesser volumes and rates of cooler runoff than the other surfaces,” says Montalto. “If we then store this runoff in cisterns and tanks, it can be made available for urban agriculture activities, for example, reducing urban potable water consumption and associated costs to property owners.”

By diverting this water from the city’s sewer system, the frequency and volume of combined sewer overflows can theoretically be reduced; this is a key benefit to water utilities like the Philadelphia Water Department and the New York City Department of Environmental Protection, two sponsors of the group’s research. 

The team is also working in a variety of urban green spaces. These include tree pits, vegetated traffic islands, sidewalk planters, constructed wetlands and urban parks. Kimberly DiGiovanni, a doctoral candidate working with Montalto, is comparing engineered green spaces to old growth forests to better understand how they partition rainwater. The goal is to understand how readily the engineered sites can be used to mitigate the effects of urbanization on the flow of water through cities, especially given potential shifts in precipitation patterns due to anthropogenic climate change.

“I’m interested in whether these engineered natural spaces really are restoring ecological functions into cities,” said DiGiovanni.

Alex Waldman, a doctoral student on the team, has been intently studying how such strategies could be integrated into other grass-roots community revitalization efforts, an important precursor to achieving wide-scale implementation.

Currently, the team’s partners include the Cramer Hill Community Development Corporation, the Camden County Municipal Sewerage Authority, the Gowanus Canal Conservancy in Brooklyn, NY, New York City Department of Parks and Recreation, Rocking the Boat in Bronx, NY and Unisphere Inc, in Queens, NY. Sponsors other than those mentioned above include the US Forest Service and the National Science Foundation. 
In addition to supervising the field monitoring efforts, Montalto collaborates with Dr. Sabrina Spatari, assistant professor of civil, architectural and environmental engineering and Dr. Ulrike Wegst, assistant professor of materials science and engineering, specifically to investigate how hydrologic changes might translate into reduced urban energy consumption and green house gas emissions. Through this research, Spatari and Wegst will be able to assess if less pumping will be required and other mechanical operations at water and wastewater treatment plants.