One reliable & comprehensive source of information about sludge and the dangers associated with its use is the Sludge-Free Alliance, based in nearby Berks County. Here’s an introductory paragraph from their website:
For just one moment, think of everything that gets flushed or rinsed down the drain… all the human waste, cleaners, poisons, soaps, and pharmaceuticals from homes combine with the waste of every business, industry, school and hospital to create a toxic stew…. The waste water treatment plant uses chemicals, minerals, squeezing, and heating to separate the sewage solids from the liquids and release the water back into our communities. The solid by-product after the water is removed from the sewage is called sludge. Sludge is tested for arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc…
Does it make sense to spread this toxic mess on the land where our food is grown?