Study of chemical coagulation conditions for a disperse red dye removal from aqueous solutions

Coagulation process using aluminum sulfate (Al2(SO4)3) and ferric chloride (FeCl3) was employed as a treatment method for decolorization of a synthetic textile wastewater containing red dye in this paper. Factors such as initial pH, coagulant dosage, initial concentration, conductivity and mixing conditions that influence color removal efficiency were experimentally tested. It was found that Al2(SO4)3 is more efficient than FeCl3 as coagulant. When 40 mgL-1 aluminum sulfate was used, results showed that color induced by the red dye was efficiently removed (>90 %) and was obtained in a large range of initial pH from 4 to 8 with, and for a dye concentration lower than 235 mg L-1. After addition of the coagulant, the medium had to be mixed for 30 min at 60 rpm, then allowed to settle for 40 min. The effects of water conductivity in the range 0.035 - 2.42 mS cm-1 and dye concentration up to 380 mg L-1 were also followed and discussed.