Maximum use of resources present in domestic "used water".

Environmental protection and the sustainable management of natural resources stand at the foreground of economic and technological activities worldwide. Current sewage technologies, however, deal with diluted wastes and do not focus on recovery and are therefore not sustainable. Here, the most promising methods available for the recovery of nutrients (nitrogen, phosphorus), organic material and energy from "used waters" are examined both at the decentralised and centralised level. Novel approaches for water processing, not implementing aerobic biological treatment as a core technology, are conceived and critically evaluated regarding efficiency, diffuse emissions and requisite costs. By implementing up-concentration of dilute wastewaters, the concentrated stream becomes suitable for the waste-to-energy strategy. The approach of up-concentration of municipal effluent at arrival at the water treatment plant followed by anaerobic digestion of organics and maximal reuse of the mineral nutrients and water is estimated to have a total cost of the order 0.9 euros/m(3); the latter is comparable to that of conventional aerobic treatment technologies which has little or no reuse. It is argued that in view of the fact that recovered nutrients will become of increasing economic and ecological value, this new conceptual design for the treatment of "used water" will become feasible in the next decade.