Experimental Investigation of Simultaneous NaCl, SO4 2-, Turbidity, and pH Removal Using Limestone-Alumina Porous Broad-Crested Weirs.

Water quality deterioration in Iraqi rivers, characterized by elevated dissolved salts, sulfates, and suspended solids, represents a critical environmental challenge that conventional solid weirs cannot address. This study presents a systematic laboratory investigation of a porous broad-crested weir (PBCW) packed with limestone (Ls) and activated alumina (Al) in four configurations (Ls, Al, Al-Ls-Al, and Ls-Al-Ls) to achieve simultaneous removal of sodium chloride (NaCl), sulfate (SO4 2-), turbidity, and pH correction. Experiments were conducted under four hydraulic regimes: through-flow, through-flow limit, transition flow, and overflow limit, with water samples collected at 10 intervals over 240 min. Results show that activated alumina consistently outperformed limestone for ionic removal, with the all-alumina configuration achieving peak NaCl and SO4 2- efficiencies of 10.6% and 9.8%, respectively, under through-flow limit conditions. Limestone configurations provided superior turbidity reduction (up to 69.3%) and pH correction (from 5.80 to 7.05). Among hybrid configurations, Al-Ls-Al delivered the most balanced multicontaminant performance and is recommended for practical deployment. Through-flow limit (Q = 1.85 m3 h-1, h1 = 10 cm) was identified as the optimal hydraulic condition across all configurations. Treatment efficiency declined progressively with time due to adsorption site saturation, with alumina exhibiting steeper decay than limestone. These results establish the PBCW as a viable passive treatment technology for decentralized, low-energy water quality improvement in water-scarce regions.