Using Plants To Purify Canal Water

The conventional way of tackling the problem would be to build a series of large water-treatment plants in the area, which covers about 300 square miles. But Alan Berger, an associate professor of urban design and landscape architecture at MIT, has another idea. Because some plants absorb pollutants as water flows by them, carefully designed wetlands can clean up the countryside while preserving its natural feel and providing public park space.

Berger realized this notion could apply to the Pontine Marshes while on a fellowship at the American Academy in Rome in 2007-2008. He then began trying to persuade officials of the Italian region of Lazio, in the province of Latina, where the marshes are located, to consider the notion. Now, after performing innovative interdisciplinary testing with researchers in MIT’s Department of Civil and Environmental Engineering, Berger believes he knows how to make the concept work best. Regional officials have since become enthusiastic about the idea: In September 2009, Lazio’s government received a grant for 4.5 million euros as part of the European Union’s “Life+” program for environmental works, specifically to clean up the area using natural processes.

That represents a reversal, Berger claims, from the response he usually got when he started floating the idea in Italy. “People said I was insane,” recalls Berger, who has designed several large-scale environmental cleanup projects in his career. “But if you do good research, you can change the type of project that is done.” As Lazio’s planning director, Carlo Perotto, said of Berger in 2008: “He opened a new way of thinking.”

Why inefficiency, here, works

As the waterways of the Pontine Marshes move from inland hills to the sea, they accumulate excess nitrogen and phosphorus from fertilizer used on the adjacent farmland. That affects the crops and livestock using the water further downstream, creating potential hazards throughout the food chain.

However, water polluted in this way can be cleansed after coming into contact with the right kind of vegetation. Marsh grasses absorb toxins and effectively remove them from circulation in the ecosystem. The wetlands Berger wants to build in the Pontine Marshes would direct polluted canal water into a twisting channel with vegetation, from which the water would emerge clean.