Biosolids soil application: Why a new special on an old issue?

The term biosolids was introduced in the early 1990s by the Water Environment Federation to define the solid, semisolid, or liquid residues generated during primary, secondary, or advanced treatment of domestic and industrial sanitary sewage sludge through one or more controlled processes that reduce pathogens and attractiveness to vectors. Although the term biosolids is related to the definition of sewage sludge, it only refers to the portion of sewage sludge that has undergone adequate treatment to permit its land application, such as anaerobic and aerobic digestion, composting, thermal or air drying, and alkaline stabilization with additives such as lime or cement kiln dust.