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

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Systems Analysis of Zaragoza UWS Guillermo Penagos emissions from composting and dewatering were the most significant impacts. Anaerobic treatment showed lower energy consumption than aerobic digestion. Swage management alternatives in contraposition form end-of-pipe technologies were evaluated by Bengtsson et al., (1997) compared conventional wastewater systems with liquid composting and urine separation. The study showed that the separation system has lower pollution loads to water and is more efficient for nutrient recycling than conventional systems. Only few studies have addressed the whole urban water cycle (Lassaux et al, 2005) and even with similar choices of system boundaries, the outcomes might be contrasting. Some publications give more importance to energy and chemical consumption, other stress groundwater withdrawal, other suggest that more attention should be given to pollution burdens (nutrients, BOD, heavy metals, etc). Results will differ from each other depending on the scale of the system, the economic development of the city subjected to study, the external activities that are considered and even the base unit for impact calculation: per year, per person and per year, per cubic meter of water. System Boundaries should be chosen according to the purpose of the study (Lundin and Morrison, 2002), but LCA is aimed to avoid planning and operation alternatives that improve environmental performance of one sub process but worsen other part of the cycle. In principle an LCA should include as many upstream and downstream externalities associated with the system as possible. Upstream activities considered in LCA studies of UWS largely focus on chemical use for both drinking and waste water treatment, energy consumption and atmospheric emissions related to transporting chemicals from producers to water facilities should be included within system boundaries. A more comprehensive approach would also include energy consumption and hazardous emissions related to the production of such chemicals (Lassaux et al., 2005; Lundie et al., 2004) Most evident downstream activity of a UWS is WW discharge. Most LCA studies also focus on sludge production and final disposal. Water recovering, nutrient recycling and minimizing hazardous emissions are the main subject here. Once again energy 12
Systems Analysis of Zaragoza UWS Guillermo Penagos consumption and atmospheric emissions derived from sludge disposal are suggested to be included within system boundaries. Another important question concerning system boundaries is water infrastructure. The usual time perspective to plan and construct a UWS is of several decades. But sustainability is a long term concept, therefore a time horizon projection of about 100 years is suggested. The construction of the water supply also may have significant environmental impacts which can be quantified such impact on the basis of the mass of material needed to construct the pipes, considering lengths, diameters and comparing different materials. Environmental Impact of putting pipes into the ground may also be considered (Lundin & Morrison, 2002) Lassaux et al. (2005) found infrastructure construction as having a significant contribution to the overall environmental impacts of the UWS. This is very important since improving WWT systems will increase environmental impacts in one way, because materials are used for construction, and then chemicals and energy are consumed. The authors also found that construction phase is responsible for important environmental impacts before tap (withdrawal pipeline, drinking water treatment, and distribution network) have less impact than stages after tap (sewer system and WWTP). In fact sewer network construction was the factor that contributed the most to the global environmental load of the anthropogenic water cycle from the Wallon region in Belgium. In contrast, Lundie et al. (2004) found infrastructure construction to contribute with less than 4% of all different categories of burdens to the environment, for both present conditions and alternative future scenarios of Sydney’s UWS. Lundie et al. (2004) used an LCA approach for assessing alternative future scenarios for strategic planning of Sydney’s UWS with a high degree of segmentation within the system. In order to select the best environmental performance different alternatives were classified after LCA in two categories: (1) options that improve the overall environmental performance and (2) options that improve one area of the system but worsen other areas. Sustainability is about management options that improve the system as a whole. This is one of few LCA studies covering the whole UWS. Main focus regarding environmental performance was given to water withdrawal and energy consumption. 13
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