An LCA framework to assess environmental efficiency of water reuse: Application to contrasted locations for wastewater reuse in agriculture

Wastewater reuse (WW-reuse) is an alternative water resource that may answer present and future water-scarcity issues, supplying diverse categories of water users: agricultural, industrial or even domestic. A literature review of 30 LCAs of WW-reuse case studies highlights that the majority are located in arid or semi-arid climates, with a third in coastal areas, thus illustrating the historical development of WW-reuse. However, the conclusions for these very site-specific cases (local conditions) cannot be extrapolated to all other situations where WW-reuse issues arise (continental location, temperate climate, etc.). The review also reveals that the assumptions and calculation approaches used in these case studies were not homogeneous. The aim of this study is therefore to propose a homogeneous conceptual framework for the evaluation of the environmental efficiency of WW-reuse, based on an adapted system boundary, a transparent and solid water balance as well as a comparison with a standardized reference system for water supply, applicable to all local situations. Through the application of this framework to urban WW-reuse for agricultural irrigation, various parameters are analysed to identify parameters that drive the WW-reuse eco-efficiency relative to archetypes of water supply mix (WSmix). Two wastewater regeneration treatment alternatives with contrasting energy demands are assessed in order to evaluate the range of reclaimed water quality that might be requested by local water policies. Four main parameters are adjusted to compare the scenarios across a panel of contrasting situations: the geographical situation (coastal or continental), the level of water scarcity, the origin of the local water resource and the composition of the electricity mix. Overall results highlight situations where reclaimed water is clearly recommended from an environmental point of view (as for coastal water-scarce situations or when compared to desalinated water) and others where it is less eco-efficient than the local WSmix (energy-intensive regeneration treatment in a continental area for instance). The nutrient content of treated urban wastewater, following denitrification during wastewater treatments, is not sufficient to provide significant environmental benefits (avoided fertilizer production) to the WW-reuse scenarios. A paradigm shift in the design of wastewater treatment plants could be a source of eco-efficiency for WW reuse, allowing for optimal recovery of the nutritional content from the wastewater.