Research on Enhancing the Performance of Pre-Treatment Systems for Saline–Alkaline Agricultural Drainage in Southern Xinjiang

Freshwater scarcity in southern Xinjiang has intensified the need for effective utilization of saline–alkaline agricultural drainage. This study evaluates pre-treatment technologies for reverse osmosis (RO) systems to improve water quality and mitigate membrane fouling. Three processes were tested: coagulation–sedimentation–media filtration (G1), micro-flocculation–media filtration (G2), and micro-flocculation (G3) combined with ultrafiltration and varying polyaluminum chloride (PAC) dosages (0–15 mg·L−1). Results show that G1 and G2 significantly outperform G3 in removing turbidity, organic matter, and inorganic ions, achieving SDI15 < 5 and turbidity < 0.3 NTU, meeting RO feedwater standards. Optimal performance occurred at the 7.5–10 mg·L−1 coagulant dosage range, effectively controlling flux decline and fouling. The integrated pre-treatment–ultrafiltration system provides a robust technical framework for saline–alkaline water desalination, offering practical guidance for sustainable water resource utilization in arid agricultural regions.