Bridging environmental and economic dimensions: A comparative techno-economic analysis of reverse osmosis and microalgae-based systems for hypersaline produced water treatment

The sustainable management of hypersaline produced water is a critical challenge for the global oil and gas industry, particularly in water-scarce regions pursuing circular economy objectives. This study presents the first comprehensive comparative techno-economic analysis (TEA) of reverse osmosis with zero liquid discharge (RO-ZLD) and microalgae-based bioremediation systems for treating hypersaline oilfield produced water at an industrial scale (15,000 m 3 /day) in the Gulf Cooperation Council (GCC) region. The analysis integrates discounted cash flow modelling, one-factor-at-a-time sensitivity analysis, Monte Carlo simulation (10,000 iterations), alternative scenario assessment, and multi-criteria decision analysis (MCDA) using the Analytic Hierarchy Process to combine economic and environmental performance indicators from a companion life cycle assessment. The base case results demonstrate that the microalgae system achieves a levelized cost of water (LCOW) of $7.11/m 3 , a 21% reduction relative to the RO system ($9.00/m 3 ), despite requiring threefold higher capital expenditure ($164.6 M versus $52.5 M). This cost advantage is driven by a 38.4% lower gross operational expenditure and $7.22 million in annual co-product revenue from algal biomass valorization. Monte Carlo simulation confirms the robustness of this advantage, yielding non-overlapping 95% confidence intervals (microalgae: $6.56–$7.82/m 3 ; RO: $7.70–$10.48/m 3 ). Under equitable regulatory assumptions incorporating ZLD compliance, the RO pathway cost escalates to $15.73–$57.70/m 3 , widening the disparity by 2.3–8.1-fold. The MCDA reveals that the microalgae system is the preferred alternative under balanced and environment-focused weighting scenarios, establishing it as a viable and economically competitive pathway for circular produced water management.