Characterization of Polycationic Bentonite Clay and its Use as a Coagulation Aid to Enhance Turbidity Removal in Water Treatment Plants

Abstract

Water is a crucial human right highlighted in the UN's Sustainable Development Goals, requiring effective treatment methods to ensure safety and quality before consumption. To meet the standards for potable water, coagulation-flocculation is among the most effective methods for treating surface water, and the enhancing the treatment of water with low turbidity typically requires the addition of coagulants. Bentonite clays are a cost-effective, efficient, readily applicable, and environmentally sound option for enhancing treatment processes. When dispersed in an aqueous solution, bentonite acts like colloidal particles, facilitating particle aggregation by neutralizing negative surface charges during interactions with coagulants. Thus, bentonite clays serve as coagulation aids; however, while this behavior is recognized, it is not yet fully understood. This study evaluated the feasibility of integrating polyaluminum chloride (PAC) and polycationic bentonite for coagulation in low-turbidity water. Thermogravimetric analysis (TGA) of bentonite showcased a total weight loss of 10.6% due to the loss of surface water and available hydroxyl groups which are responsible for increasing its ability to interact with dissolved compounds. Fourier Transform Infrared (FTIR) and X-ray Diffraction (XRD) analyses revealed the presence of montmorillonite, while zeta potential analysis indicated an average potential of -36.60 mV, which is characteristic of materials that form stable dispersions in water. The optimal coagulant (PAC) dosage increased almost linearly with the initial turbidity of the raw water, being 17 mg.L⁻¹ Al₂O₃, 35 mg.L⁻¹ Al₂O₃, and 45 mg.L⁻¹ Al₂O₃ for average initial turbidity of 7.6 ± 0.5 NTU, 21.3 ± 0.8 NTU, and 29.6 ± 0.9 NTU, respectively. Incorporating bentonite as a coagulant aid results in significantly improved turbidity removal across a range of initial raw water qualities, yielding treated water with 28%-57% less turbidity compared to using only PAC for coagulation. Additionally, color removal efficiencies higher than 86% were attained when PAC and bentonite were added to low turbidity raw water.