The escalating global freshwater scarcity, particularly in coastal regions with extreme salinity such as the Persian Gulf (~TDS 45000-70000 mg/L), has intensified the demand for sustainable, energy-efficient, and reliable industrial-scale desalination solutions. This study presents the design, full-scale implementation at a steel manufacturing complex, and operational performance evaluation based on continuous, calibrated measurements over 12 months, of a two-pass reverse osmosis (RO) system, comprising a seawater RO (SWRO) first pass followed by a brackish water RO (BWRO) second pass, developed to produce ultra-pure process water from hypersaline Persian Gulf seawater. All results derive from actual full-scale plant operations (no simulation), with hourly data logging for recovery, TDS, pressure, and fouling indicators. The plant operated at a feed flow rate of 51.5 m³/h, first-pass pressure of 69.6 bar, second-pass pressure of 11.0 bar, and overall system recovery of 31%. Under steady-state operation, the system consistently produced 16.0 m³/h of permeate with a total dissolved solids (TDS) concentration of 4.33 mg/L (<5 mg/L standardized units), which is significantly lower than typical industrial ultra-pure water standards (<10 mg/L) and well below typical SWRO permeate TDS for hypersaline feeds (300–800 mg/L), often reported in the range of 20–50 mg/L. The SWRO stage achieved a recovery of 36.1% with salt rejection exceeding 99.6%, while the BWRO stage further polished the permeate at a recovery of 86%, reducing the final TDS to below 5 mg/L. Measured ion rejection efficiencies for key constituents, including sodium (Na⁺: 97.5%), chloride (Cl⁻: 97.5%), and sulfate (SO₄²⁻: 99.2%), surpass conventional two-pass SWRO-BWRO benchmarks (monovalents 95–97%, divalents 98–99%) under hypersaline conditions. Operational assessment of scaling and corrosion tendencies, specific to Persian Gulf seawater chemistry, revealed a Langelier Saturation Index (LSI) of +1.55 in the SWRO concentrate, indicating a high risk of calcium carbonate scaling, while the BWRO permeate exhibited an LSI of -5.85, indicating strong corrosivity. These risks were effectively controlled through optimized recovery distribution, targeted antiscalant dosing (0.5–1.2 mg/L as per industrial practice), and appropriate material selection, consistent with best industrial practices for high-salinity RO systems. The measured total specific energy consumption (SEC) of the integrated system was 8.27 kWh/m³, comprised of 6.73 kWh/m³ for SWRO and 0.45 kWh/m³ for BWRO. This SEC aligns competitively with hypersaline SWRO systems without ERDs (7–10 kWh/m³), higher than large-scale SWRO with ERDs (3–4 kWh/m³) but optimized for ultra-high purity (<5 mg/L TDS) and reliable small-scale industrial operation without ERDs. This demonstrates a well-balanced trade-off between energy efficiency and separation performance for industrial-scale operations. Overall, the full-scale two-pass SWRO–BWRO system exhibited high operational reliability, technical feasibility, and consistent production of ultra-pure water from hypersaline Persian Gulf seawater. The system met stringent industrial water quality standards, optimized energy consumption, and mitigated scaling and corrosion risks, confirming its suitability as a scalable and sustainable desalination solution for industrial facilities in water-stressed coastal regions.
Mohammadi et al. (Wed,) studied this question.