Cradle-to-grave life cycle assessment of membrane distillation systems for sustainable seawater desalination

Membrane distillation (MD) is an emerging seawater desalination technology capable of utilizing low-grade heat. Many studies have been dedicated to MD systems design; however, few have offered comprehensive life cycle assessment (LCA). This paper develops a cradle-to-grave LCA framework for MD systems to shed some light on the environmental performance of MD technology. The MD systems consist of direct contact/air gap MD modules, heat exchangers, pumps, pipelines, and other equipment of heat sources. The MD modules comprise membrane, housing, condenser, and spacer. The heat sources are geothermal and solar energy, with auxiliary power from the grid and renewable energy sources. Life cycle inventories of the major components of the systems are established for the assessment. The ReCiPe 2016 method is chosen in this paper, including 18 midpoint indicators and three endpoint damage indicators. Results suggest that the major environmental impacts of renewable energy-driven MD desalination plants arise from the construction materials for the heat sources and the auxiliary power consumption in the operation stage. The environmental impacts can be reduced by 24.57%-70.79% when the auxiliary electricity supply from the grid is switched to renewable energy sources.