Sewage sludge application - or biosolids - is a highly regulated field. Assuming everyone is following the laws - set forward by the EPA and enforced by each state’s environmental regulatory arm - biosolid application should be fine. There are limits of the heavy metals allowed per square foot, etc. Typically, industrial sludge still goes to landfill.
Septage - or the liquid from septic tanks - is untreated. That is not the same thing. Biosolids have been through a wastewater treatment facility suitable for land application - not food crops, though. It doesn’t smell great, but in theory, shouldn’t be harmful. Lots of folks question whether the pathogens can survive the process and would be harmful to animals and humans. Other folks question whether the regulation process is sound - in other words, are there more heavy metals - like molybdenum for one - that kinda stuff being put back in too high a concentration.