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Article Highlights• Development of a clean process for indigo dyeing • Substitution of conventional sodium dithionite by green alternatives in reducing indigo• Study of synergy effect of mixture α-hydroxycarbonyls in reducing indigo • Determination of the optimum mixture of α-hydroxycarbonyls for reducing indigo Abstract Textile industries use different chemicals in dyeing processes, consuming large quantities of water and producing large volumes of wastewater. For the particular case of indigo dyeing processes, its reduction is performed chemically by the addition of sodium dithionite. However, this is considered environmentally unfavorable because of the resulting contaminated wastewaters. Therefore, it is important to replace sodium dithionite with other alternatives in order to achieve cleaner processes. α-hydroxycarbonyls have been suggested as possible environmentally friendly alternatives to reduce indigo. However, each one applied alone is unable to attain the dyeing performances offered by the conventional reductant. Thus, the study of the synergy of some selected α-hydroxycarbonyls was proposed. In this paper, a mixture design of experimental (DOE) methods was used to determine the optimum combination of α-hydroxycarbonyls to be applied in the indigo reduction process. Based on the design expert software, quadratic models were established as functions of α-hydroxycarbonyls ratios. The diagnostics of models were investigated by using mixture contour plots. Finally, a model was proposed to predict the optimum conditions leading to dyeing performances exceeding those obtained from the reduction of indigo by the conventional sodium dithionite.Keywords: green reducing agent, α-hydroxycarbonyls, synergetic effect, mixture design, clean process.As a vat dye, indigo is considered the oldest dye known to man. It is an organic compound with a distinctive blue color. Historically, it was naturally extracted from plants, and this was important economically because blue dyes were rare. Nearly all indigo dyes produced today -several thousand tons each year -are synthetic. Indigo and other vat dyes consumption reaches about 33×10 6 kg annually [1]. This

Treatment of Indigo dye (leuco form), reduced in the industrial conditions of the SITEX (Textile Industrial Company), by a batch electrocoagulation using aluminum electrodes. Response Surface Methodology (RSM) and Box-Behnken design were used to optimize for Color Removal (CR(%)). Our results showed that the quadratic second order equation provided the best correlation for the decolorization of Indigo dye (CR(%)). On the other hand, the ANOVA analysis proved the large interaction between the current intensity and the initial concentration of the dye. Experiments were conducted to find the desired conditions for removal of particular concentration of the dye and lower Operation Cost. The results showed that CR(%) = 88.3% (R 2) of color removal for initial dye concentration of 12.31 mg/l, with a current density of 2.81 A/m 2 , solution concentration of NaCl of 2.67 g/l. Under these conditions, Electrical Energy Consumption (EEC) and Electrode Consumption (EMC) and Operation Cost were 0.01999 kWh/m 3 (R 2 = 93.1%), 0.00142768 Kg/m 3 (R 2 = 79.4%

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a b s t r a c tNovacron Blue 4R (NB4R) dye was removed in a semi-continuous process treatment by electrocoagulation-flocculation-filtration. Our results showed that the quadratic second order equation provided the best correlation for the decolorization of NB4R dye (CR%). On the other hand, the regression equation proved the large interaction between the current intensity and the initial concentration of the dye. Experiments were conducted to find the desired conditions for removal of the dye and lower Operation Cost. The results showed that CR% = 90.84% (R 2 = 95.8%) of color removal for initial dye concentration of 30 mg/L, using a current intensity of 1 A and a flow rate of flocculent (FRF) injected of 9.14 mL/min. Under these conditions, electrical energy consumption (