What are biosolids?

Biosolids isn't just a fancy term for excrement. Biosolids do come from sewage or sludge but biosolids have gone through some form of treatment to eliminate odors and control potential spread of disease. Excrement is organic material rich in nutrients, but can also contain organisms such as bacteria, viruses, and parasites that are pathogenic or vectors of disease. But those nutrients make biosolids a desirable alternative to chemical fertilizers. But how do we make them safe for use?