Evaluation of carboxymethylpullulan-AlCl₃ as a coagulant for water treatment: A case study with kaolin

A reduction in the use of aluminum (Al)-based flocculants in the treatment of drinking water is considered essential for human health reasons. In this study, a novel composite flocculant, made of carboxymethylpullulan-AlCl₃ , is evaluated in a lab-scale, jar test system for the flocculation of kaolin. The results showed that the coagulation efficiency of carboxymethylpullulan-AlCl₃ was more effective in reducing turbidity than the solo use of carboxymethylpullulan or AlCl₃ . The optimum treatment conditions assessed by a response surface methodology were obtained at pH 6.50, 13.03 mg/L carboxymethylpullulan, and 94.87 mg/L AlCl₃ . Zeta potential measurements and photometric dispersion analysis demonstrated that AlCl₃ had a more significant influence on charge neutralization than carboxymethylpullulan, whilst carboxymethylpullulan facilitated absorption and the development of particle bridges. Thus, the composite flocculant possessed both advantages that enhanced flocculation, and decreased the dosage of AlCl₃ , thereby reducing the potential for secondary environment pollution. When 90 mg/L carboxymethylpullulan-AlCl₃ was added to the model kaolin suspension characterized by a turbidity of 50 nephelometric turbidity units, the zeta potential and the maximum flocculating activity were determined as -2.28 mV and 98.0%, respectively. The results provide insight into the development of an environment-friendly composite flocculant prepared from water-dissolved polysaccharide and inorganic flocculants. PRACTITIONER POINTS: A novel composite flocculant CMP-AlCl₃ was achieved by combining CMP and AlCl₃ for water treatment. The coagulation efficiency of CMP-AlCl₃ was more effective in reducing turbidity than the solo use of CMP or AlCl₃ . The flocculation efficiency and mechanism were investigated by Zeta potential analysis, surface morphology, electron microscopy, and coagulation.