What does ‘biosolids’ specifically refer to?

Biosolids specifically refer to treated organic material that comes from the sewage treatment process. After wastewater is treated to remove contaminants, the remaining solids are further treated to stabilize them and reduce pathogens, making them safe for beneficial use. This treated material can be used as organic fertilizer, enriching soil and supporting plant growth, thus playing an important role in waste recycling and sustainable agriculture.

The other options are not applicable when defining biosolids. Raw wastewater contains a mixture of water and contaminants, and solid waste from landfills generally refers to refuse and not processed organic material. Chemically treated waste does not convey the same meaning as biosolids, which emphasizes the biological treatment aspect rather than solely chemical intervention.