closed loop systems

Looking for information on closed loop biological water recycling. I am working on a new project, see http://www.mj3.biz/biz/storage/IndianSprings-current.pdf.
The aquaponics system is closed loop but the human/waste loop on the outside is open. In this particular area, arid desert, pushing toward closed loop would be desirable. The aquaponics system is a biologcal filter, not mechanical or chemical. So I would like the equivalent on the outside loop. I see this as a opportunity to do some closed system testing while being useful in the real world.
Does anyone know the status of SSI's E-lab research? Or URLs to other implementable technologies? What would really help is some detailed data on water safety requirements vs biological waste systems. I have never really understood how dumping waste water back into a river to be used by the next town down the river was any different from sending it back into the pipes.
Mitchell James