Each day, when four million Angelenos flush the toilet, most of the waste flows to the Hyperion Treatment Plant, adjacent to Los Angeles International Airport. After the waste is treated with biological, chemical, and physical processes, the city is left with 700 tons -- the equivalent weight of 350 SUV's -- of biosolids: organic matter that is rich in nutrients and stripped of harmful pathogens and some odors.
As this "SoCal Connected" segment discussed, much of the biosolids are trucked to a city-owned farm in Kern County called Green Acres. There, it's used as fertilizer to grow things like wheat and corn, which are fed to livestock and zoo animals.
But the Green Acres farm accounts for only about 80 percent of L.A.'s biosolids. What happens to the rest? It only goes to a few other places.
About 10 percent of the city's biosolids ends up in an unlikely place: one mile beneath Terminal Island in Long Beach and San Pedro harbors. Beginning six years ago, L.A. embarked on a first-of-its-kind, experimental project to pump biosolids into emptied oil and gas reserves. Deep underground, the earth's heat will break down the biosolids. Eventually, the organic material will yield methane gas, while the rock traps carbon dioxide. The well has already produced methane, but not enough to capture and use, sanitation spokesperson Diane Gilbert said.
The city will continue its experiment at Terminal Island until at least the end of 2018, when its permit is set to expire. "Our experimental objectives are to see how much storage we can get, and how fast gas can be generated," said Gilbert.
Still another portion, 100 tons per week, goes to Griffith Park, where it's mixed with plant trimmings and waste from zoo animals -- known as "zoo doo" -- and composted. After fifteen days, the compost heap is ready to be used as fertilizer in city parks, schools, and the L.A. Zoo.
The small remainder of biosolids gets shipped to Kern County, San Bernardino County, or Arizona by a contractor. Some of this is applied to land, just like the waste taken to Green Aces, and some of it goes to factories that produce fertilizer.