Substance flow analysis as a tool for mitigating the impact of pharmaceuticals on the aquatic system
Introduction
The presence of pharmaceuticals in surface water around urban areas was highlighted by several researchers during the last decade (Alder et al., 2001; Kolpin et al., 2002; Schowanek and Webb, 2002; Bendz et al., 2005; Zuccato et al., 2006; Van De Steene et al., 2012). Indeed, pharmaceuticals consumed by humans are excreted in urine and faeces as parent compounds or metabolites and enter the sewage system; they usually reach the wastewater treatment plant (WWTP), where they are partially removed before being discharged into surface water (Kümmerer, 2008). Many of these substances are of major concern regarding their possible long-term impacts on both humans and the aquatic environment (Fent et al., 2006; Jones et al., 2005; Kostich and Lazorchak, 2007; Dussault et al., 2008). Scientists and engineers therefore came to the conclusion that reducing pharmaceuticals and, more generally, micropollutant discharge from urban areas is of high priority (Kümmerer, 2008; Williams, 2005; Ternes and Joss, 2006).
In recent years, an increasing number of research has been undertaken to investigate different technical solutions to remove pharmaceuticals in the WWTP (Ternes and Joss, 2006; Miège et al., 2008). Common investigated technologies include ozonation combined with sand filters (see for example Nakada et al., 2007; Kim et al., 2008) or activated carbon (see for example Roswell et al., 2009) combined or not combined with nanofiltration (Kazner et al., 2008) or ultrafiltration.
However, wastewater discharge is not the only way for pharmaceuticals to reach surface water. During rain periods, mixtures of stormwater and wastewater are also rejected in the aquatic system through combined sewer overflows (CSO). These episodic discharges are rarely taken into account despite the fact that they may contribute to an important aquatic contamination, and can sometimes present a risk for the aquatic organisms (Even et al., 2007; Weyrauch et al., 2010; Phillips et al., 2012). Therefore, the management of pharmaceuticals in urban areas should take into account all emission sources to the aquatic system, and should also include the impacts of these discharges on the receiving environments. A holistic view of emissions and risk for the aquatic environment is thus needed for the mitigation of pharmaceutical impacts.
In this paper, we propose such an approach based on substance flow analysis (SFA). Briefly, SFA describes and quantifies the material flows through a defined system, and has been originally proposed for regional analysis by Baccini and Brunner (1991). Later the SFA was enhanced with modelling concepts to allow simulations on the basis of current system knowledge (Baccini and Bader, 1996; Bader and Scheidegger, 2012). Such an approach was successfully used for phosphorous management in a large city (Huang et al., 2007). Furthermore, different studies in Switzerland and in Austria demonstrated its potential as a basis for river basin pollution control with respect to nutrients (Lampert and Brunner, 1999; Sarikaya et al., 1999; Somlyódy et al., 1999). A SFA was also tested and validated for heavy metals (Chèvre et al., 2011) for the same region of interest presented in this paper. This latter study focused on stormwater discharges carrying organic and inorganic substances to the aquatic environment mainly during rain events (Burton and Pitt, 2002; Rossi et al., 2004). The SFA, as proposed in this last study, allows modelling with little data and profound system knowledge. Measurements, literature values and estimations or plausible reasoning can be used as input data.
The overall goal of this paper is to use SFA as a tool for the implementation of strategies aimed at reducing the risk of pharmaceutical discharges in the aquatic environment. We will base our investigations on the city of Lausanne, whose CSOs, stormwater and WWTP ends up in the Bay of a large lake, Lake Geneva. This lake serves as a recreational area and is an important source of drinking water for more than 600,000 habitants (www.cipel.org). Two sources of pharmaceuticals will be considered, namely urban and hospital consumption. Discharges into the lake can occur via WWTP and CSOs. Finally, the environmental risk for the aquatic life in the Bay will be used as an indicator to evaluate the current state and to select the best strategy.
Section snippets
Substance flow analysis
The analysis of the contribution of the different discharges to surface water was performed using a mathematical substance flow analysis (Bader and Scheidegger, 2012). Such an analysis is based on the principle of mass balance: a substance enters a closed system and may be transported or transformed in the system, and may also leave the system. In our case, the system is defined by the sewer catchment and the receiving water, the bay of Vidy in Lake Geneva.
The SFA proposed in this study is
Substance flow analysis
Fig. 2 presents the SFA for the four pharmaceuticals. The loads are given in [kg/year]. The dominant input in the system for all pharmaceuticals is the human consumption in the city. However, for ciprofloxacin, entry into the sewer system from the hospitals represents 30% of the total input, and for the other three substances between 7% and 9%. For some specific pharmaceuticals, hospitals can therefore be an important source of water pollution, as already highlighted by Langford and Thomas
Conclusion
This study showed that SFA constitutes a very interesting tool for describing pharmaceutical behaviour in the urban water system and for developing the best strategy for pharmaceutical elimination. Indeed, the results show that the contribution of CSO to surface water pollution is low compared to that of the WWTP. The improvement in the treatment at the WWTP will thus significantly reduce the impact on the aquatic system, whatever the method chosen for chemical removal. However, in certain
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