3.2.3 Substances flow analysis in Vasastaden, Göteborg
Substances flow analysis for different sewage systems have been performed in Vasastaden,
Göteborg by Ahlman et al., (2004). The study showed that there is no benefit to introduce a source
separating system for blackwater, if the sludge cannot be recycled to agriculture or land where the
conventional sewage sludge is not accepted. Further, the total cost to build separating sewage
systems will be 30 times higher for nitrogen and app. 200 times more expensive for phosphorus.
This makes it not reasonable to reconstruct present sewage systems only looking at nitrogen and
phosphorus (Ahlman et al., 2004). There would be possible to find other solutions at the source or
the treatment plant, which give less cost per kg recovered phosphorus respectively nitrogen. The
introduction of source separating systems has not reach satisfaction in the hygiene and the
environmental area state Ahlman et al., 2004.