For millennia, people around the world have used human excreta on fields as fertilizer, making good use of the energy and nutrients it contains, such as nitrogen, potassium and phosphorus.
Today, the same principle is used in the application of sewage sludge to agricultural fields. After sewage is processed to extract and clean wastewater, what’s left is a semi-solid mass known as biosolids. Good-quality, uncontaminated biosolids are applied to fields around the world, especially in Europe and Japan. But fertilizing fields with biosolids must be done with great care, because biosolids can contain pathogens, heavy metals, industrial chemicals, pharmaceuticals and so on.
Biosolids can also be used for forest remediation, to fill landfill sites and for urban landscaping. They are a useful feedstock for biodigesters or can be incinerated for heat recovery and electricity generation. Biosolids can even be used as a building material, such as for pavement materials or building bricks.