After cities have cleaned out waste in water treatment plants, they're left with clean water and something called sewer sludge that's packed with human waste, toxins, and other impurities you wouldn't want in your water. Kansas City treated it like other cities and burned it in incinerators. Until they realized its value.
Now the city uses the sludge as fertilizer on its 1,340 acres of city-owned corn and soybean fields. Don't worry, the crops aren't used for human (food) consumption. Instead, the city sells the crops to biofuel makers. It's an endeavor that's turned into a money maker for the city, The Kansas City Star reports:
The ingenious part of the equation is that Kansas City has made $2.1 million in net income over the past six years doing something that used to cost it money.
“That is fantastic,” said Tammy Zborel, who works with a sustainability program for the National League of Cities. “That is not a common practice for cities to engage in that level of farming.”
The city still uses the incinerator for some of the sewer sludge, but it's only a fraction of the amount it uses on the fields. In 2011, 9,982 tons of sludge were used as fertilizer, while only 2,044 tons were incinerated. Impressive.
Kansas City-owned farm turns human waste into revenue [Kansas City Star]