Pretreatment of a dyeing wastewater using chemical coagulants

For pretreatment of the feed water of membrane processes, chemical coagulants such as HOC-100A, alum, and ferric chloride were used. The feed water used in this experiment was a synthetic dyeing wastewater composed of Direct Red 75, polyvinyl alcohol (PVA), NaCl and Na2SO4. Total concentration of the materials in the feed water was 2500 ppm. The following optimum coagulation pretreatment conditions were sought using jar tests: for HOC-100A, the concentration of HOC-100A was 2000 ppm at the coagulation pH 7, for aluminum sulfate, 4000 ppm at pH 7, and for ferric chloride, 1500 ppm at pH 10. Under optimum conditions for all the coagulants used, about 90% of materials was removed from the solution when checked with the UV absorbance of the solution before and after treatment.