LCI model and tool for chemicals discharged down the drain. Case study on detergent formulations
Muñoz I, Van Hoof G, Rigarlsford G (2016)
Presentation for the 22nd SETAC Europe LCA Case Study Symposium, Montpellier, 20-22 September 2016. Slides available here: WW LCI_SETAC Montpellier.
Existing models for wastewater treatment in LCA reflect average conditions in wastewater treatment plants (WWTPs), rather than the specific fate of particular chemicals and they omit the impact of direct discharges. We present a model and tool to calculate life cycle inventories (LCIs) of chemicals in wastewater, WW LCI. It attributes the exchanges with the technosphere and the environment taking into account the expected behaviour of individual chemicals. The model covers treatment of organic and inorganic chemicals and the WWTP is modelled taking into account the partitioning of each chemical to air, sludge, treated effluent, and depending on its degradability, the transformation by microorganisms to CO2 and excess sludge. Sludge is treated by anaerobic digestion and the fate of any fraction of chemical released to the environment (e.g. treated effluent, direct discharges) is assessed in terms of greenhouse-gas (GHG) as well as nutrient (N, P) emissions following degradation in environmental compartments. Sludge disposal includes incineration, landfilling and agricultural reuse. The model is programmed in Excel and accommodates simultaneous calculations for 30 chemicals, either individually or as a mixture. The resulting LCIs can be automatically imported into the LCA software SimaPro.
The applicability of WW LCI is shown in a case study on three detergent formulations (powder, liquid, concentrate) including 28 chemical ingredients. The impact of these formulations is assessed for a functional unit of one wash, and the results are compared to those of the WWTP model developed for ecoinvent v2. The system boundaries include only the end-of-life stage, i.e. discharge of the three formulations after use in a washing machine, and the impact categories assessed are GHG emissions, freshwater and marine eutrophication and freshwater ecotoxicity.
The results show that, when assessed individually, the impact of some chemicals can be orders of magnitude different when assessed with the ecoinvent model and with WW LCI. When assessed as a mixture (detergent formulations), differences are lower between models and the ranking of formulations is not changed. The main advantages of WW LCI over the ecoinvent model are that it addresses the impacts from direct discharge, relevant for developing countries where connection to WWTPs is limited, and second that it provides a complete substance flow analysis of the assessed chemicals across all environmental impact categories.