When I worked with our family farms (2005 through 2012), my family had used bio-solids extensively since 2002. They would vary the land type where they applied it, and do the soil testing and nutrient management planning to use the appropriate biosolid type to balance soil pH (high lime or low lime biosolid).
I started studying what was happening biologically. The biosolids I tested were bacterially dominated, so their use (especially repeated use) caused more weeds to grow, because the biosolids made the soils more bacterially dominated over time, instead of building the 1:1 Fungal to bacterial ratios needed for healthy row crops and grasslands. The forms, rates, and pulses of nitrogen produced in the bacterially dominated soil stimulated weed seed germination and growth versus grasses or crops.
If you know me you know I am all in favor of putting manure on the land…but letting the animals do it naturally and the dung beetles and earthworms take the poo into soil rapidly, or properly composted with carbon to build the proper fungal to bacterial balance for healthy crops.
Lastly, many cities do not separate their human poo from the industrial and medical waste streams. There are many chemicals used in households and prescription drugs flushed down the toilet each day. So the biosolids needs to be biologically re-mediated to be truly healthy. Just using lime to kill e.coli and mediate pH is not the full answer.
Plants and microbes can bio-remediate and photo-remediate a lot of our wastes, but personally for my farm I do not use the commercially available biosolids. I use our animals for our fertility and do not need to import more.
Lastly, It is critical that even those who disagree with their use take a hard look at our waste streams and what we are creating. We all are part of the problem…but it is our own intersection with these “problems” where the opportunity lies for healing!