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

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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 38
Systems Analysis of Zaragoza UWS Guillermo Penagos for 75% of the total load to the river. Once again “Almozara” and “Paper mills” loads are quite comparable. Nearly 60% of nitrogen is being removed from the sewage by the WWT system and ends up in the sludge (no data concerning denitrification were available). Since “Cartuja” plant is designed to remove phosphorus, the relative contribution of this facility to the TP loads to the Ebro River is relatively low as compared with all other pollution loads that have been already mentioned and it is even comparable to those loads from the other two facilities. As consequence of TP removal at “Cartuja” plant 65% of this nutrient is disposed in a landfill for hazardous materials (see figure 2) and only 3.5% is recycled to agriculture. 39
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