Removal of selected azo dyes from textile wastewater by chemical coagulation/flocculation: implication of the dye destabilization mechanism

The results of the coagulation/flocculation of six commercially used textile azo dyes coagulated with synthetic primary coagulants are discussed in the paper. Surface charge measurement of coagulated dye-flocs was employed to find a correlation between its sign and the level of colour removal. Additionally, flocs characterization was done with the aim to link data with surface charge and on this basis to outline the predominant mechanism of colour removal. Based on the results obtained, the evident correlation between surface charge density progression of coagulated dye flocs and colour removal after different solid/liquid separation methods was observed. Thus, it was concluded that the charge neutralization was the predominant mechanism responsible for dye destabilisation. It was found out also that flocs produced at optimal dosage are characterized by large median size and high value of fractal dimension