What's the history of sewage treatment? How do biosolids fit in?
Waste disposal is a fact of life. Even the Bible includes instructions for disposing of our excrement: "And thou shalt have a paddle upon thy weapon; and it shall be, when thou wilt ease thyself abroad, thou shalt dig therewith, and shalt turn back and cover that which cometh from thee." (Deuteronomy 23:13)
According to a fascinating article that appeared in Scientific American called "How Does Sewage Treatment Work?", before indoor plumbing, the average person used less than five gallons of water every day. Now that we can flush -- U.S. residents use about 100 gallons of water use a day. That's a whole lot of wastewater that's got to go somewhere.
For years big cities in the U.S. took that water and dumped it directly (sans treatment) into whatever big body of water was nearby. In San Diego, for example, up until 1943 raw sewage went straight to the Pacific Ocean and San Diego Bay. Not good for swimming, that's for sure.
Why not recycle some of that waste instead? People started treating, processing, and turning their wastewater into "biosolids". Biosolids are the byproducts of the wastewater treatment process (they are not "raw" human waste, so don't freak out). They can come as liquids, soils or pellets and are often used to help fertilize crops and improve land.
Milwaukee has been making a product called Milorganite for decades (see photo above); they sell it at big box stores to homeowners in search of lush lawns. A 36-pound bag will cost you about $15 from Amazon.com.
(For you film buffs out there, apparently Milorganite makes an appearance in the movie "Caddyshack".)
The EPA has guidelines (PDF) about the amount of pathogens and chemicals that can be contained in biosolids applied to land.