Assessing urban wastewater system upgrades using integrated modeling, life cycle analysis and shadow pricing

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INTRODUCTION
Sustainable development has now been adopted as an overarching goal of all economic and 31 social development by multiple United Nations agencies, individual nations, local governments 32 and corporations 1 . Prerequisites for this are decisions encompassing technical economic, social 33 and environmental considerations 2 . For urban wastewater systems (UWSs) management this 34 integration can only be achieved through the integration of state-of-the-art tools that support 35 decision making. 36 Water management agencies are already conducting several studies to ensure the operation of 37 the UWS adheres to these principles (for example the KALLISTO project 3-6 by the Waterschap 38 de Dommel (WdD)). These studies have evaluated the cost-effectiveness and the technical 39 performance of various proposed UWS upgrades, often looking at the ecological improvement of 40 the receiving water body. An important tool in these analyses has been integrated modeling, 41 encompassing the whole UWS and receiving medium and enabling dynamic assessments of the 42 systems at hand 3-8 . Despite the great strides made during these assessments, some aspects often 43 remain unaddressed -primarily global and long-term environmental impacts. 44 Life Cycle Analysis (LCA) is a technique to quantify the impacts associated with all the stages 45 of a product, service or process from cradle-to-grave, in order to evaluate the environmental 46 impact of its entire life cycle 9 . The application of LCA allows for the assessment of secondary, 47 global impacts brought about by the proposed measures for UWS upgrading. There have been biochemical processes of the whole system (sewer system, WWTP and receiving water body). 53 For this purpose we employ an integrated model of the UWS -already used in previous studies [3][4][5][6] 54 -which has shown to be a powerful tool to analyse and evaluate the proposed measures. This 55 allows for a more integrative analysis as well as climatic and seasonal variations in the influent 56 composition. The river model allows for the consideration of its functions and its capacity to 57 dilute and uptake the discharged loads. Integrated modeling also provides the ability to 58 investigate the dynamic effect of operational changes and upgrades on the assessment of the 59 LCA impact categories. 60 Weighting is an optional step during a LCA and it can be used to include a prioritisation of the  20 . Currency appears to be a unit that can be easily integrated by 68 decision-makers in the decision process and be contrasted against other indicators 19,21 . It is also a 69 unit that is easily understandable and communicable by a wide range of decision-makers 22 .

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Valuation aims to express the value society puts on them in monetary terms for purposes of 71 assessment and internalisation 23 . By attaching a value on an emission the estimated 72 environmental damage (or 'cost') can be an indicator of the environmental losses for the society 73 regarding its present and future emission goals 24,25 . This a largely vague undertaking, mainly 74 hindered by the fact that in many cases no market exists for elements such as water quality or 75 The studied system is the Eindhoven WWTP and its collection system, located in the southeast  Table 1.  In this study we employ shadow prices to attach weights on the estimated impacts. Uncertainty  Table 2 and Supporting Information Tables S1 (for sludge treatment

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The data regarding outputs to water, electricity use and sludge production were obtained using depletion) can then be seen looking at the "Outputs to water at the end the river reach" (Table 2) 203 of each measure. The specific contribution of CSO events to the total outputs to water is 204 provided in detail in Table S4 of the supporting information for the base case and measure D

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(storage tanks). The total contribution of CSO events to the ammonium loads emitted appeared 206 to be a small part of the overall emissions (less than 1.2%), as well as the contribution of the 207 phosphorus loads (7.7% and 4.8% for the base case and measure D equivalently), attributed to 208 the fact that the total CSO volume is less than 4% the WWTP effluent volume over 10 years.   Table S9.

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Due to the disparity between the values as well as possible theoretical preferences (e.g. damage 250 versus abatement) all three sets were applied for weighting, as a means of addressing the 251 uncertainty behind their estimations and their relative importance.