Deer Island Sewage Treatment Plant, Massachusetts

The Deer Island waste treatment plant processes Boston's sewage and is the second largest sewage treatment plant in the country (Chicago's is larger). The plant is capable of handling more than a billion gallons of wastewater per day, ejecting treated effluent out giant submerged sprinkler heads at the end of a 9.5-mile long 24-foot-diameter tunnel that leads out to sea. A dozen "egg-shaped" digesters, each around 130-feet tall, loom over the island, and break down solids in the waste. The city's sewage, treated and untreated, has been pumped out to sea from here since 1899.