Removal of dyes and industrial dye wastes by magnesium chloride

Magnesium chloride, as compared to alum and polyaluminium chloride (PAC) is a less commonly used coagulant in the field of wastewater treatment, with a cost in between alum and PAC. It has been used in this study as a coagulant to investigate the effectiveness in the chemical precipitation method for the removal of colouring matters. The colour concentration of dye solutions was measured by visible spectrophotometry. Parameters such as the effect of pH, the effect of coagulant and coagulant aid dosages and the effect of different coagulants have been studied. The results show that MgCl2 is capable of removing more than 90% of the colouring material at a pH of 11 and a dose of 4 g MgCl2/l of dye solution. MgCl2 is shown to be more effective in removing reactive dye than alum and PAC in terms of settling time and amount of alkalinity required. Optimal operating conditions such as pH value, coagulant dose and effect of polyelectrolyte have been determined. Wastewaters of a dyeing and printing mill on different days have been treated by MgCl2 aqueous solution in bench scale. The treatment of the industrial waste has shown a reduction of 88% in COD and 95% of suspended solids.