Environmental performance and design trade-offs of a multi-stage zero liquid discharge desalination brine valorization system: An ex-ante life cycle assessment

Frameworks for management and valorization of desalination brine are increasingly investigated as circular economy solutions for a globally significant waste stream. However, the environmental trade-offs associated with integrated zero liquid discharge (ZLD) systems remain poorly understood, particularly at early stages of technology development. This study applies an ex-ante life cycle assessment (LCA) to evaluate four alternative configurations of a multi-stage brine valorization system against conventional direct brine discharge. The assessment is based on laboratory-scale experimental data and incorporates chemical precipitation, membrane separation, thermal concentration, crystallization, and flotation processes to recover magnesium, calcium, potassium, sodium salts, and high-purity water. Environmental impacts were quantified per cubic meter of seawater reverse osmosis reject brine treated using either direct discharge or resource recovery pathways. Environmental impacts were quantified using ReCiPe 2016 Midpoint (H), with an added impact indicator to better assess brine discharge-related impacts. Results showed that scenarios using Ca(OH)₂ for magnesium precipitation consistently outperformed those using NaOH, mainly due to lower burdens from alkali production. The best-performing scenario achieved lower impacts than direct brine discharge in 9 of 18 midpoint categories, also eliminating localized aquatic ecotoxicity impacts and providing circularity benefits. However, climate change, acidification, and fossil energy use impacts remained higher than those of the reference scenario, caused mainly by electricity consumption in the MED stage. Sensitivity and scenario analyses confirmed that environmental performance is strongly influenced by electricity demand, chemical inputs, and the background electricity mix. The findings demonstrate the potential of the ZLD system, the value of ex-ante LCA as a design-support tool and highlight the importance of energy efficiency and electricity decarbonization.