I propose for the sanitation of black water as opposed to the grey water that should be going to agriculture we use a leach field system that pumps out the black water into a large open swamp for use by plants like lillies,cattails,reeds and other native swamps plants that use it and filter it over a long winding course that sends it over many levels till it gets to a clean enough state to water the grazing pastures or orchards. this is both economic and self repairing as nature will grow to accomedate the amount of food you give it therfor increasing the filter strength.
that could work for a small city, but what about the scalability of such a system?
after a certain amount of time, things might get a little backed up. Also, we would need to worry about the spread of certain bacteria and diseases.
