CREDIT: ISTOCKPHOTO (toilet); SOURCE: “CHARACTERIZATION, RECOVERY OPPORTUNITIES, AND VALUATION OF METALS IN MUNICIPAL SLUDGES FROM U.S. WASTEWATER TREATMENT PLANTS NATIONWIDE,” BY Paul WESTERHOFF ET AL., IN ENVIRONMENTAL SCIENCE & TECHNOLOGY. Published online JANUARY 12, 2015

For more sewage moneymaking schemes, see Steve Mirsky's Anti Gravity column.