Good day Chris. I noted your ...

Good day Chris. I noted your interest in this topic of biosolids and and application. 
In the application to land there would be the 3 stages of the wastewater treatment. Primary, Secondary and Tertiary. As it pertains to biosolids, the primary screening would remove the large items and plastics in a mechanical grid. This would be best landfilled (but perhaps a case by case basis). 
Secondary treatment and flocculation and settlement ponds - that would produce the good stuff! The sludge would have "dried sufficiently by solar exposure and be treated with lime to reduce pathogens and odors. 
Now regards application to land - in Britain we had the Safe Sludge Metrix! There are parameters for contaminants, certain metals and chemicals, and pathogens. Random testing ascertains the suitability of the sludge - lets give an example. Leafy vegetables are as a rule incompatible, whereas orchards of peeled citrus would be ideal. 
If the biosolids are of a lower grade - i.e. some exceedence of thresholds - these would be applied to reclamation of mining quarries etc - where the waste could be dumped into furrows and these used to plant trees. 

My favorite is the dissication and the manufacture of Sewage Derived Fuel pellets that can be co fired in a if i recall the technical design parameter a Fluidised Bed (a grate with oxygen added to the combustion in a Coal Powerstation), or added to a Biomass Burner too. 

There is also the interm potential to utilise the Sewage Sludge as Biogas if sufficient nitrogen can be introduced, and the correct innoculant, and then the liquid sludge be applied to agricultural land chiefly fodder crops like silage. 

Success.