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

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Systems Analysis of Zaragoza UWS Guillermo Penagos mostly available only in hard copies. When specific information concerning Zaragoza system was not available, the extrapolation of general information has been considered. 3.2.4 Data analysis A water balance was performed from the information available at Zaragoza municipality (figure 2, and annexes). Mass balances were performed for BOD 5 , COD, TN, TP and Heavy metals at the WWTPs. As shown in Annex 1 there are several processes for which there are no data available at Zaragoza municipality. For such processes, assumptions and extrapolations from literature values were made. A description of these assumptions and calculations is provided next. 3.2.4.1 Storm water No data concerning storm water quality exits in Zaragoza (which is understandable for a semiarid region) therefore the possible effects of storm water upon WWT performance are completely unknown. The possible effect of storm water upon the Ebro River is here extrapolated from the chemical characteristics of sewage and the possible overflows, which have not been actually measured, but have been estimated as follows (for raw data and calculations for storm water refer to annexe 10): Estimated storm water = Precipitation * impervious area Overflows = Estimated storm water + Expected WWTPs inflow – Actual inflow to WWTPs Daily precipitation data for Zaragoza was provided by the Local Agenda 21 Office at Zaragoza municipality. There were no data concerning evaporation, extrapolation was made from Marti (2000). 3.2.4.2 Energy consumption and CO 2 emissions from transportation Environmental impacts derived from transporting both chemical products and sludge were calculated as energy consumption and CO 2 emissions to the atmosphere. Factors from Thonstad (2005) were used (for raw data and calculations refer to annex 9) 18
Systems Analysis of Zaragoza UWS Guillermo Penagos 3.2.4.3 CO 2 Emissions from electricity consumption Raw data concerning energy consumption of the DWTP and the WWTPs were provided by the Local Agenda 21 Office at Zaragoza. The derived CO 2 emissions were calculated regarding the electric energy sources in Spain provided by Ministerio de Industria, Turismo y Comercio de España (2007) referred in figure 9. Emission factors from European Commission (1995) were used (for raw data and calculations refer to annex 8). 3.2.4.4 CO 2 production from sludge Wastewater sludge emits CO 2 as a function of the OM concentration. Raw data regarding wastewater sludge production at the WWTPs were provided by the Local Agenda 21 Office at Zaragoza municipality. COD content in the sludge was calculated from the mass balance between inflow and outflow load at each facility. Multiplication factors from Levlin (2005) were used to calculate TOC content and CO 2 : TOC = 40% of COD CO 2 = 3.66*TOC 3.2.5 Scenario analysis Based on the collected data, an exercise for Scenario Analysis is presented following the methodology suggested by Assimacopoulos (2007) in which the main drivers for change and sustainability are identified by means of a problem tree analysis. Drivers are qualitatively discriminated under the criteria of importance and uncertainty. Possible scenarios resulting from the combination of drivers considered as more important and more uncertain are set. Finally strategies to cope with such scenarios are suggested. The aim of the strategies is to adapt the system to reach a sustainability vision. 19
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