Sludge is the muddy material left over from treating everything that goes down a sewer. It consists of human excrement mixed with prescription drugs, solvents, cosmetics, heavy metals, pesticides, plastics, and thousands of industrial chemicals.
Prior to the 1970s, the EPA considered sewage sludge "hazardous waste." Prior to the 1970s, most of our food wasn't grown in it.
But in the 1970s, when the EPA acknowledged that treatment plants "would be generating 10 million tons of sludge per year, a thought that 'gives us all a massive environmental headache,' " they OK'd its use as a "soil conditioner."
"As budget concerns mounted in the late 1970s, the EPA began to pressure sewage plants to adopt the cheapest method available [for disposal]--spreading sludge on farm fields."Here's an excellent documentary on waste and the consequences of spreading sludge on farmland by the National Film Board of Canada. (It's available on DVD, but I've embedded the entire 52 minute film below for free. Double-click along the time bar to skip through it.)
That alternative in the end, the composting toilets, I don't know about that. Do you think it would take off?
Crapshoot: The Gamble with Our Wastes
Jeff McKay, 2003