Impacts from urban water systems on receiving waters – How to account for severe wet-weather events in LCA?

Abstract

Sewage systems are a vital part of the urban infrastructure in most cities. They provide drainage, which protects public health, prevents the flooding of property and protects the water environment around urban areas. On some occasions sewers will overflow into the water environment during heavy rain potentially causing unacceptable impacts from releases of untreated sewage into the environment. In typical Life Cycle Assessment (LCA) studies of urban wastewater systems (UWS), average dry-weather conditions are modelled while wet-weather flows from UWS, presenting a high temporal variability, are not currently accounted for. In this context, the loads from several storm events could be important contributors to the impact categories freshwater eutrophication and ecotoxicity. In this study we investigated the contributions of these wet-weather-induced discharges relative to average dry-weather conditions in the life cycle inventory for UWS. In collaboration with the Paris public sanitation service (SIAAP) and Observatory of Urban Pollutants (OPUR) program researchers, this work aimed at identifying and comparing contributing flows from the UWS in the Paris area by a selection of routine wastewater parameters and priority pollutants. This collected data is organized according to archetypal weather days during a reference year. Then, for each archetypal weather day and its associated flows to the receiving river waters (Seine), the parameters of pollutant loads (statistical distribution of concentrations and volumes) were determined. The resulting inventory flows (i.e. the potential loads from the UWS) were used as LCA input data to assess the associated impacts. This allowed investigating the relative importance of episodic wet-weather versus "continuous" dry-weather loads with a probabilistic approach to account for pollutant variability within the urban flows. The analysis at the scale of one year showed that storm events are significant contributors to the impacts of freshwater eutrophication and ecotoxicity compared to those arising from treated effluents. At the rain event scale the wet-weather contributions to these impacts are even more significant, accounting for example for up to 62% of the total impact on freshwater ecotoxicity. This also allowed investigating and discussing the ecotoxicity contribution of each class of pollutants among the broad range of inventoried substances. Finally, with such significant contributions of pollutant loads and associated impacts from wet-weather events, further research is required to better include temporally-differentiated emissions when evaluating eutrophication and ecotoxicity. This will provide a better understanding of how the performance of an UWS system affects the receiving environment for given local weather conditions.

Assessing environmental impacts of large centralized wastewater treatment plants with combined or separate sewer systems in dry/wet seasons by using LCA

“…It can be seen that, the selection of appropriate functional unit is prominent as the total treated water discharge volume to the environment is more in the wet season than the dry season, leading to the possible higher total pollutant mass load to the environment. It is noteworthy that although FU1 has been widely used for seasonal LCA assessment of WWTP Lorenzo-Toja et al 2016;Li et al 2017;Risch et al 2018), effects from the variation of influent compositions and flow could not be reflected very well if only using per unit volume as a functional unit (Rodriguez-Garcia et al 2011;Piao et al 2016). The functional unit as per kgPO 4 3 -eq removed based on eutrophying substances removal (e.g.…”

“…Since 1990s, LCA has been applied to the field of wastewater treatment (Corominas et al 2013). In a study with LCA, Risch et al (2018) reported that loads from storm events contributed significantly to eutrophication and ecotoxicity of WWTPs in Responsible editor: Philippe Loubet Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11356-020-08038-2) contains supplementary material, which is available to authorized users.…”

“…The square of correlation coefficient, R 2 , between flow rate and average monthly rainfall ranged from 0.21 to 0.85, indicating that the flow rates of wastewater to WWTPs with combined sewer systems in different catchment areas were affected by rainfall intensity to different extents (Mines et al 2007). It is believed that highly pollutant loaded influent in dry season can usually have satisfactory levels of pollutants removal while diluted influent by storm water is prone to cause operational issues (Lorenzo-Toja et al 2015;Risch et al 2018), and lower treatment efficiency. In many cases, however, lower effluent pollutant concentrations were reported from WWTPs during wet weather due to the dilution of wastewater (Joel et al 2017;Li et al 2017).…”

Passive samplers to quantify micropollutants in sewer overflows: accumulation behaviour and field validation for short pollution events

“…In case of rain events, untreated wastewater and stormwater may be discharged via sewer overflows to creeks and lakes, when the hydraulic capacity of either wastewater treatment plant or of sewer system locally is exceeded. These discharge events can negatively impact natural aquatic environments since organic pollutant concentrations may exceed environmental quality standards (Launay et al 2016;Mutzner et al 2016;Risch et al 2018;Brudler et al 2019). In stormwater, the occurrence of polar organic pollutants (pharmaceuticals, pesticides subsequent referred to as contaminants) depends strongly on local factors, including land use, substance application, rain fall intensity and duration, as well as dry periods between storms.…”

Peer Review #1 of "Assessment of the ecotoxicity of urban estuarine sediment using benthic and pelagic copepod bioassays (v0.1)"

“…The growing demand for resources and services has increased the pressure for agricultural and industrial activities, and urban development (Neumann et al 2015;van Vliet et al 2015). Estuaries have become highly vulnerable to this pressure, due to the continuous input of municipal, agricultural and industrial runoff, storm water discharges and accidental wastewater overflows (de los Ríos et al 2016;Risch et al 2018;Rodrigues et al 2017;Willis et al 2017). These stressors, added to the increase in sedimentation have made estuaries a sink for pollutants with affinity for small particles (Reichelt-Brushett et al 2017;Swales et al 2012;Vermeiren et al 2016).…”