As the children’s book has it, everyone poops. By and large, in the developed world, this means the toilet flush is our last contact with what might be our lowest common denominator.
But what comes next? That poo, after all, goes somewhere. And in America, it basically means that local municipalities make a choice: human waste can go to a landfill, a field, or an incinerator.
The landfill and the incinerator seem clear enough, but can we really put human waste on the fields where we grow our food, or play with our kids?
Human waste becomes “sludge” when it passes through municipal water treatment facilities, and it can be treated and turned into Class A or Class B biosolids (as defined by the EPA).
In terms of land application (spreading the biosolids on the ground as fertilizer), exceptional quality—Class A—biosolids can be used in small amounts with no buffer requirements or crop type/harvesting restrictions. These “exceptional quality” biosolids meet EPA requirements for low levels of metals and bugs.
If used in large quantities, Class A biosolids do have buffer requirements, but no crop harvesting restrictions.
Class B biosolids, on the other hand, basically always have buffer requirements, public access, and crop harvesting restrictions (Class B biosolids are treated, but still contain detectible levels of metals/pathogens).