Abstract
Decentralized greywater reuse presents a viable pathway toward alleviating severe water stress in Mediterranean regions; however, the environmental trade-offs across the complete life cycle of nature-based treatment systems remain insufficiently characterized. This study performs a comprehensive cradle-to-grave Life Cycle Assessment (LCA) of decentralized horizontal subsurface flow (HSSF) and vertical subsurface flow (VSSF) constructed wetlands designed for residential greywater treatment and non-potable reuse (toilet flushing and landscape irrigation). Using a functional unit of 1 m3 of treated effluent over a 30-year system lifespan and applying the ReCiPe 2016 Midpoint and Endpoint (H) methods alongside the AWARE water scarcity indicator, primary empirical data gathered from pilot installations in a semi-arid Mediterranean basin were evaluated. Results indicate that the construction phase represents the primary contributor to environmental impacts, with quarrying, aggregate transport, and high-density polyethylene (HDPE) geomembranes responsible for over 68% of the embodied Global Warming Potential (GWP) and Mineral Resource Scarcity. The VSSF configuration exhibited a 22% lower GWP (0.41 kg CO2-eq/m3) compared to the HSSF configuration (0.53 kg CO2-eq/m3), primarily driven by its smaller footprint and reduced media volume. When accounting for the displacement of conventional municipal water supply, both systems yielded net-negative environmental impacts in Water Consumption (-0.91 m3 world-eq/m3) and mitigated marine eutrophication. These findings confirm that decentralized subsurface constructed wetlands, particularly VSSF systems utilizing localized aggregates, serve as ecologically sound infrastructure for bolstering water security in drought-prone Mediterranean climates.
