+1 zeuspaul
To avoid biosolids, again buy products with the Organic Materials Review Institute
OMRI seal.
Biosolids are prohibited under OMRI.
The
Mulch & Soil Council (link to pdf) and
US Composting Council do not prohibit biosolids.
If you are ok with biosolids, the highest quality is
Class A Exceptional Quality. Milorganite falls under this category with strict standards regarding pathogens, metals, odors, and vectors.