Treatability of a simulated disperse dye-bath by ferrous iron coagulation,ozonation, and ferrous iron-catalyzed ozonation

Dyeing and finishing of textile yarns and fabrics are extremely important p rocesses in terms of both quality and environmental concerns. Among the com mercial textile dyes, particularly disperse dyestuffs are of environmental interest because of their widespread use, their potential for formation of toxic aromatic amines and their low removal rate during aerobic waste treat ment as well as advanced chemical oxidation. Thus, in the present paper fer rous iron coagulation, ozonation and ferrous iron-catalyzed ozonation were employed at varying pH (3-13) and Fe(II)-ion doses (0.09-18 mM) for the tre atment of a simulated disperse dye-bath (average initial apparent color as absorbance at 566 nm = 815.4 m(-1); COD0 = 3784 mg l(-1); TOC0 = 670 mg l(- 1); BOD5,0 = 58 mg l(-1)) that more closely resembled an actual dyehouse ef fluent than an aqueous disperse dye solution. Coagulation with 5000 mg l(-1 ) FeSO4. 7H(2)O (18 mM Fe2+) at pH 11 removed up to 97% color and 54% COD, whereas oxidation via ozonation alone (applied ozone dose = 2300 mg l(-1)) was only effective at pH 3, resulting in 77% color and 11% COD removal. Fe( II)-ion-catalyzed ozonation (3.6 mM Fe2+ at pH 3; Fe2+:O-3 molar ratio 1:14 ) eliminated 95% color and 48% COD and appeared to be the most attractive o ption among the investigated chemical treatment methods as for its applicab ility at the natural acidic pH of the disperse dye-bath effluent and at rel atively low Fe2+-ion doses as compared to ferrous sulfate coagulation. Howe ver, no TOC reduction was observable for ozonation and catalytic ozonation at the investigated reaction conditions (14 gl(-1) O-3 at pH 3). An average six-fold enhancement in the biodegradability parameter of the synthetic dy e wastewater expressed in terms of the BOD5/COD ratio could be achieved by the investigated chemical treatment methods. (C) 2001 Elsevier Science B.V. All rights reserved.