Coagulant Blends in Surface Water Treatment: Purification Effects, Chemical Stability Impact, Global Warming Potential, and Practical Considerations

This study evaluated inorganic-organic coagulant blends for surface water treatment, focusing on purification performance, chemical stability, environmental impact, and potential practical applications. The blends consisted of poly(diallyldimethylammonium chloride) (polyDADMAC) combined with either aluminum sulfate (ALS) or polyaluminum chloride (PAX-XL 19 F). Laboratory-scale coagulation tests were conducted using two dosing strategies: a fixed dose of one coagulant combined with increasing doses of the other. Treatment performance was assessed based on color, turbidity, permanganate index (PI), and ultraviolet absorbance at 254 nm (UV 254 ). Chemical stability was evaluated using the Langelier Saturation Index (LSI), Ryznar Stability Index (RSI), Puckorius Scaling Index (PSI), Larson Ratio (LR), and saturation indices. The production-related Global Warming Potential (GWP) of the inorganic coagulant components was also estimated. The most effective treatment configurations were achieved when polyDADMAC was applied at a fixed dose of 2.5 mg/L while the dose of the inorganic coagulant was increased. The polyDADMAC/ALS blend at 2.5/22.0 mg/L and the polyDADMAC/PAX-XL 19 F blend at 2.5/19.3 mg/L achieved comparable color removal (66.67 ± 12.47% and 66.67 ± 4.71%, respectively) and turbidity removal (85.20 ± 4.58% and 84.64 ± 5.93%, respectively). The PAX-XL 19 F/polyDADMAC blend demonstrated greater PI removal efficiency and a less pronounced impact on water chemical stability. However, replacing ALS with PAX-XL 19 F resulted in a higher estimated production-related GWP. Overall, the results indicate that coagulation using selected coagulant blends can effectively support the preliminary treatment of surface water for drinking water production as well as selected non-potable applications.