Applying Biosolids to Land in Michigan
Biosolids are solid, semisolid and liquid residues generated during the treatment of sanitary sewage, or domestic sewage, in treatment works treating domestic sewage (TWTDS). The term was introduced by the wastewater treatment industry in 1991 to describe the residuals or solids created during the biological treatment of wastewater (hence “biosolids”). The wastewater treatment process that produces biosolids is schematically shown in Figure 1. The Michigan Department of Environmental Quality (MDEQ) has also adopted this term for rules made effective in November 1999.
Like animal manure, biosolids are part of the natural cycle of life. They contain inorganic and organic compounds removed during wastewater treatment. The beneficial use of biosolids for land application allows for the nutrient content and soil amendment properties of these residuals to be used advantageously for sustained crop production. For decades, biosolids (previously called sewage sludge) have been used with great success on agricultural lands throughout the world. Land application has been increasingly regulated to protect human health and the environment from various constituents that can be found in biosolids, such as bacteria, viruses and other pathogens (i.e., disease-causing organisms); metals (e.g., cadmium and lead); toxic organic chemicals (e.g., PCBs); and nutrients (the most important being nitrogen and phosphorus). Forty years of research and demonstration projects on applying biosolids to land lead to the conclusion that agronomic use of high quality biosolids is sustainable and very safe.