Biosolid

The Clean Water Act requires that communities treat their wastewater to return this resource safely to the environment. When wastewater is treated, the process produces a semisolid, nutrient-rich byproduct known as biosolids. When treated and processed properly, biosolids can be recycled and applied to crop land to improve soil quality and productivity because of the nutrients and organic matter that they contain. Historically called sewage sludge, biosolids is the term now used to emphasize the beneficial nature of this recyclable material. Biosolids often contain approximately 93 to 99 percent water, as well as solids and dissolved substances present in the wastewater or added during wastewater or biosolids treatment processes. The quantity of municipal biosolids produced annually in the United States has increased dramatically since 1972, from roughly 4.6 million dry tons in 1972 (Bastian, 1997) to 6.9 million dry tons in 1998. This is a 50 percent increase from 1972, when the Clean Water Act first imposed minimum treatment requirements for municipal wastewater, and is greater than the 29 percent increase in U.S. population from 1972 to 1998 (Council of Economic Advisors, 1999).
source:  EPA website - A report on Biosolids Generation, Use, and Disposal in The United States