Investigating coagulation behavior of chitosan with different Al species dual-coagulants in dye wastewater treatment

Abstract

In this study, chitosan (CS) was used as a coagulant aid with different Al species (Ala/Alb/Alc) to treat disperse yellow (DY) wastewater. The effects of coagulant dosages and initial pH on color removal, floc structure and regrowth were investigated. Results showed that the efficiency could be significantly improved with the addition of CS, due to the strong interaction between flocculants and Al species–dye aggregates. CS with the protonation of amino groups could combine with the azo bond and methyl of DY wastewater. Moreover, larger flocs would be generated as CS was added, especially at lower Al dosages. Based on the experimental results of this research, the initial solution pH had an impact on the hydrolysates of Al species and charge of CS, and further influence the color removal efficiency and floc properties. The color removal efficiency was relatively large at pH 6.0–7.0. The bigger flocs were formed under alkaline condition for Ala and its dual-coagulant, and under acidic condition for Alb/Alc and the corresponding dual-coagulants, respectively. In coagulated water, the values of strength and regrowth also increased as CS was dosed, due to the introduction of bridging and charge neutralization.