In the United States alone, billions of gallons of water are treated each day at wastewater treatment facilities. Once the water is clean, a different challenge remains: determining what to do with the solids that are removed during the treatment process. The resulting mixture is often a unique semi-solid blend of organic and inorganic materials, trace elements, chemicals, and even pathogens, so there is no across the board solution for handling and processing the combinations of constituents that may be present.
Because these solids are often rich in nutrients, like nitrogen and phosphorus—which also happen to be the perfect ingredients for promoting healthy soil and plant growth—many facilities have turned to land application. Before these solids can be put to use for things like fertilizing farmland, however, they must undergo rigorous treatment to meet stringent regulations, at which point they become known as biosolids.