Comparative life-cycle assessment of reverse osmosis and microalgae-based treatment for hypersaline oilfield produced water

The management of hypersaline produced water (130–190 g L −1 TDS) from oil and gas operations—especially in regions with carbon-intensive grids like Kuwait—poses significant environmental and operational challenges. Its high salinity requires energy-intensive treatment, leading to considerable greenhouse gas emissions and resource depletion. This study addressed these challenges by conducting a cradle-to-grave life cycle assessment to quantitatively compare the environmental performance of conventional reverse osmosis (RO) and an open-pond microalgae-based treatment system. Using the ReCiPe 2016 method and Kuwait-specific grid data, the assessment evaluated trade-offs across eight impact categories. The microalgae system showed a substantial advantage in global warming potential, achieving a net-negative value of −0.15 kg CO₂-eq per cubic meter of treated water, compared with 17.7 kg CO₂-eq emitted by the RO process. Furthermore, the microalgae system provided a net credit for fossil resource scarcity (−0.193 kg oil-eq) and reduced freshwater eutrophication by 60 % relative to RO. However, it also presented important trade-offs, including a 2.19-fold increase in land use, a 9.7-fold increase in marine eutrophication driven by the nitrogen content of the glucose feedstock, and higher human carcinogenic toxicity. Monte Carlo analysis confirmed strong robustness in the comparative ranking for seven of the eight impact categories, with water consumption being the only exception. To address these trade-offs, the study recommends strategic siting on non-arable coastal land, deployment of land-efficient photobioreactor designs, and development of hybrid RO–algae configurations. As the first assessment of hypersaline-produced water under Gulf grid conditions, this work underscores the potential of microalgae-based treatment as a low-carbon and resource-efficient alternative. • Microalgae treatment achieves net-negative GWP, outperforming energy-intensive RO. • System yields fossil resource credits and lowers overall water consumption. • Human non-carcinogenic toxicity significantly reduced compared with RO treatment. • Trade-offs include higher land use and elevated marine eutrophication. • Hybrid RO–algae strategies and coastal siting mitigate environmental burdens.