“I am going to spend the next couple of minutes talking about poop,” the New York City-based architect Ate Atema told his audience at the New York Times Cities for Tomorrow Conference, which took place in early July.
According to Atema, more than 700 cities have “major poop problems” because they depend upon antiquated combined sewer systems, which mix sewage with storm water.
Atema’s topic was apt for a conference about the future of cities, because combined sewer overflows (CSOs) constitute one of the biggest environmental threats to metropolitan areas like New York. As little as a tenth of an inch of rainfall in New York City is enough to cause a CSO. When that happens, sewage-laced storm water is released into the city’s harbor and its rivers, where it kills aquatic life, spreads vapors linked to diseases and causes beach closings. At the conference, Atema said that New York City generates up to 27 billion gallons of this malodorous cocktail annually, enough to fill a 10-foot-diameter pipe stretching from Bangkok to Times Square.
With cities getting bigger, the sewage problem is just getting worse. In cities such as New York, replacing existing combined sewer systems with separate pipes for storm water and sewage is not an option because it would be prohibitively expensive and disruptive. However, expanding the capacity of the existing system also is a costly undertaking. New York City has committed to a multi-billion-dollar plan to build new sewage treatment plants as well as a novel green storm-water infrastructure program to reduce the flow of storm water. The green elements that the city is building include green roofs and bioswales, which are planted areas that filter polluted water.