Effects of pH and Coagulant Dosage on Effectiveness of Coagulation of Reactive Dyes from Model Wastewater by Polyaluminium Chloride (PAC)

This study measures the influence of pH and polyaluminium chloride (PAC) dosage on the effectiveness of reactive dyes removal. Experiments were carried out for turquoise DG, red DB-8, orange OGR and black DN. The pH was changed from 3.5 to 7.0 and the dosages of PAC from 0.3 to 4.0 mg Al/mg dye. The degree of dyes removal depended on pH and dosage of coagulant. In the pH range from 4.0 to 5.5 the optimal dosages of coagulant were: 0.5 mg Al/mg dye for turquoise DG and black DN, 1.0 mg Al/mg dye for red DB-8 and orange OGR. In pH range from 6.0 to 7.0 diminished effectiveness of coagulation was observed; the decrease was most in the case of red DB-8. At the optimal coagulant dosages colour removal depended on the initial concentration of dye. Minimal efficiency of dye removal was measured for small concentrations of dyes, e.g. 25 and 50 mg/dm. From among the examined dyes the highest degree of colour removal was obtained for turquoise DG and the lowest for red DB-8. Qmax from Langmuir isotherm expressed as mg dye/mg Al, was 2.1 for turquoise DG and 1.2 for red DB-8.