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

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Systems Analysis of Zaragoza UWS Guillermo Penagos 4.3.6 Sludge production Figure 17 shows the annual production of sludge (dry matter) produced by Zaragoza UWS. Here both DWT and WWT sludge are presented together. Clearly those two are completely different kind of waste and impact the environment in different way. However, solid waste production as such is generally used as environmental performance indicator for urban systems. Hence it is also considered here as well. It is evident that solid waste production from this UWS has significantly increased from 2001. The reason is that DWTP began dewatering sludge from 2002. From 2003 DWT sludge becomes the major component of solid waste for the water system. Total solid waste from the water system is around 14,000 ton year -1 . According to the Local Agenda 21 Office this amount represents around the 4% of total solid waste produced by the city every year. 16 DWTP Cartuja Almozara Paper mills 14 Sludge (10 3 ton) 12 10 8 6 4 2 0 2001 2002 2003 2004 2005 2006 Year Fig 17. Sludge (as dry matter) production by Zaragoza UWS 4.4 Zaragoza UWS in the future The vision of Zaragoza for its UWS has been focused on water supply. The main goal was to reduce water withdrawal to 65 million 3 year -1 by 2010 and has already been achieved. Other goal is to reduce unaccounted tap water below 15%, but there is no time horizon for this goal. However this indicator has been reducing 2% per year on average since 2002 when the plan for improving water supply started (see table 2). If the city manages to keep decreasing unaccounted water at such rate, it will reach 15% by 2015. 42
Systems Analysis of Zaragoza UWS Guillermo Penagos Other aspects of environmental urban water sustainability are not expressed as goals for the water system. However Zaragoza city signed the Aalborg summit for sustainable European cities. The goals of Zaragoza sustainability vision that apply to the UWS and a list of suggested actions to achieve each goal are shown in table 5. Table 5. Goals of the Aalborg summit that apply to the UWS of Zaragoza Goal Necessary actions to achieve the goal 1 To reduce water withdrawal Water recycling, infrastructureupgrading (on going action), demand management (demo activity within the SWITCH project) 2 To reduce unaccounted water Infrastructure upgrading, demand management 3 To improve water supply quality Shifting to a different raw water source (on going action), shifting to a different DWT technology 4 To contribute to improve the ecological Status of the Ebro River 5 To reduce dependence on fossil fuels To reduce pollution loads to the River Shifting to renewable energy sources (depends on National Government Policies) 6 To reduce the ecological footprint To reduce resource consumption 7 To reduce the production of solid waste To reduce sludge production 4.4.2 Focus problem and drivers affecting Zaragoza sustainability vision The tree problem methodology is used here to define the goal of environmental sustainability as the focus problem of Zaragoza UWS. Several drivers that might affect the environmental performance of such system are shown in figure 18. 43
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