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

Systems Analysis of Zaragoza UWS
Guillermo Penagos
2%
11%
48%
13%
1%
Pb
Cu
Hg
Ni
Zn
As
25%
Figure 12. Heavy metals in Zaragoza waste water
Figure 13 shows the heavy metal annual loads from Zaragoza UWS to the
environment. WWT technologies in Zaragoza are not designed to remove those,
therefore it is not surprising that nearly 60% of total load every year is going to the
Ebro river. Around 80% of the loads to the river are produced by “Cartuja” plant.
“Almozara” produces loads that are quite similar to those from “Paper mills”. The
impact of storm water is considerably low. Around 39% of heavy metals from sewage
is disposed at landfill site and only a negligible fraction (around 1%) ends up in
agriculture fields. Total annual loads to the river are around 23 ton year -1 whereas
total loads to landfills are around 13 ton year -1 . Loads to agriculture are 300 kg year -1 .
Comparison between years shows only small differences with no clear tendency of
heavy metal loads to either increase or decrease over time.
4.3.4 Organic matter
Biodegradable and non-biodegradable organic matter loads to the Ebro River
expressed as BOD and COD respectively are shown in figure 14. BOD loads are
around 1,000 ton year -1 and COD loads are around 4,500 ton year -1 . Again around
80% loads come from “Cartuja” plant and loads from “Almozara” plant and from
“Paper mills” are similar. Again the impacts from storm water are relatively low except
for the year 2001 when it produced half of BOD load, increasing the city total two
folds. COD load from storm water in the same year was not as high as BOD load, but
it was comparable to those of “Almozara” and “Paper mills”.
4.3.5 Nutrients
Just as other pollution loads previously described annual loads of nitrogen and
phosphorus do not show any tendency to either increase or decline over the years.
Nitrogen loads to the Ebro River are around 3,000 ton year -1 . “Cartuja” plant accounts
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