Systems Analysis of Zaragoza Urban Water - SWITCH - Managing ...

Systems Analysis of Zaragoza UWS
Guillermo Penagos
1. Phosphorus
2. Non biodegradable organic matter
3. Nitrogen
4. Heavy metals
5. BOD
This is a very interesting outcome that reflects several internal aspects of Zaragoza
UWS as well as its relation to the surrounding environment.
Secondary WWT via activated sludge is a technology for BOD removal and it works
quite well on this regard. Therefore it is possible to say that improving BOD removal
is not a priority for this UWS.
Since activated sludge is a biological treatment it does not work that well to remove
non biodegradable OM, remaining COD in treated sewage has got a relatively high
impact on the receiving water body.
Zaragoza WWT system is not designed to remove nitrogen. However biodegradable
OM removal is also removing about 40% nitrogen from sewage. The remaining 60%
is still high but it does not seem to have an important impact on the Ebro River, which
might be explained by the fact that nitrogen concentrations in the river are already
high (see table 7).
Concerning heavy metals, again it is important to say that Zaragoza WWT system is
not designed to remove those, nearly 40% are retained by the sludge though. Also
untreated Zaragoza sewage does not contain high heavy metal concentrations.
Therefore this impact is not that significant.
Concerning phosphorus it is possible to say that 68% of Zaragoza WWT system
(Cartuja plant) is actually designed to remove phosphorus. However the
effectiveness of this technology is just around 80%, in addition to this, the combined
impact of Almozara and paper mills WWTPs, which do not remove nutrients, is so
important that TP has got a large impact on the Ebro River. Therefore reducing
phosphorous loads may be considered as the priority for improving Zaragoza UWS
with regard to the Ebro River.
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