i think the alternatives would probably come about far easier if the city upstream would treat its water properly.
>
...- most
>urban sewage is human waste.
some things to consider...
a significant number of cities have "combined sewer systems" which treat stormwater and sanitary sewage together during rain events. stormwater usually has the really nasty stuff in it. heavy metals, petroleum, dioxins, rats, rubbers, and needles just to think of a few. add to that industrial flows-some pretreated, some not-and you have a witches brew of shit!
i'm not necessarily challenging the concept of sewage treatment, but means to the end. there are documented technologies that can be used to treat the human sanitary sewage and deal with the toxic shit that can use natural systems and achieve exceptional results.
as with all technologies that actually seem to help humanity, these things are generally suppressed by some sort of powerful financial interest. this time its the wastewater-industrial complex.
aml