All systems are acceptable in the hygiene and environmental load. In the point of view in resource
usage, blackwater has with urine separation an essential lower exergy usage than other systems and
the system with local treatment plant has the highest exergy usage (as exergy is the qualitative
energy). The local solutions are considerable more expensive than when the city is fully connected
to the large scale system (1). The total cost is such high that it is not defendable with the potential
exergy saving, but must be motivated with demand on recycling/recovery of pure nutrients via a
process, which is driven by a decreased adding of process chemicals.
The results indicate that source separating systems qualitative can be seen to have larger technical
risks than the combined system. Chemical risks need more data to make a quantative risk judgement
of the different systems.