Decolorization of reactive dyes using inorganic coagulants and synthetic polymer

A coagulation/flocculation process was employed for the treatment of high concentration reactive dye wastewater. A polymer flocculant synthesized from cyanoguanidine and formaldehyde under acidic conditions was applied with inorganic coagulant (alum or ferric salt) for the dyeing wastewater. The flocculant was tested for synthetic wastewater containing four model reactive dyes (Black 5, Blue 2, Red 2 and Yellow 2) and real wastewater containing reactive dyes from a local dyeing industry. For the synthetic wastewater, the use of inorganic coagulant (1 g/L) alone achieved only 20% of color removal or less. However, with the aid of polymer flocculant, almost 100% of color removal was obtained. The dye removal efficiency increased as polymer dose increased and the efficiency was affected by solution pH and types of the used inorganic coagulant. The use of inorganic coagulant alone appeared little effective in the removal of reactive dyes from the real wastewater. However, alum/polymer and ferric salt/polymer combinations improved color removal up to 60% and 40%, respectively.