Comparative life cycle assessment of membrane distillation for inland concentrate management

Membrane Distillation (MD) is an emerging thermally-assisted desalination process that can produce high-quality water from high-salinity streams using low-grade heat, thus supporting near-zero liquid discharge. To adopt MD as a concentrate management technology, it is essential to compare environmental and economic implications of MD to conventional management alternatives. This work presents a comparative environmental life cycle and cost assessment of MD and conventional concentrate management technologies (i.e., evaporation ponds, deep well injection (DWI), mechanical concentrators) for the treatment of saline streams. Environmental impacts are quantified as a single score in points/m³ (pt/m³). Results indicate that MD has the second lowest environmental impact scores, with a range between 0.02 and 0.04 pt/m³ and cost from 0.81 to 1.52 USD/m³. Although evaporation ponds and DWI have some of the lowest environmental impacts (0.01–0.13 pt/m³) and disposal costs (1.05–6.77 USD/m³), the application of these technologies are limited to geographical constrains (e.g., climate and geology). Additionally, despite the low environmental impact of evaporation ponds and DWI, they do not place value on resource recovery. Finally, although brine concentrators offer a modular and scalable approach to concentrate management, they have the highest impacts and costs ranging from 1.04 to 1.18 pt/m³ and 7.47–7.94 USD/m³, respectively. In each system, the main environmental and cost stressors can differ, signifying the lowest cost does not always align with the lowest impact – underscoring the need for tailored treatment solutions. Overall, results support MD as a cost-competitive concentrate management technology with low environmental impacts and the added benefit of producing high-quality water.