Comparison of sludge settling velocity and filtration time after electrocoagulation process in treating industrial textile dyeing wastewater: RSM optimization

Abstract

Electrocoagulation process (EC) is one of the best economic methods for industrial textile dyeing wastewater treatment; however, produced sludge is the main problem of this method. So sludge settling velocity (SSV) and filtering time (FT) of sludge are effective on area requirement and operating costs. Effect of four operational parameters including electrodes type, pH, current density and electrodes distance was investigated on SSV and FT. Decolorization and chemical oxygen demand (COD) removal of wastewater were checked. The results showed the more effect of electrodes type rather than of variable parameters. SSV and FT were 0.02–0.14 cm/min, 0.2–8.34 min for Al electrodes and 0.05–1.55, 0.42–2.78 min for Fe electrodes at all conditions. Also decolorization and COD removal were 62–94.5, 14.74–36.74% for Al electrodes arrangement and 83.91–94.59, 24.6–44.45% for Fe electrodes arrangement. Comparison between Al and Fe electrodes showed that Fe electrodes were better than Al for filtration and settling after EC process. Fe electrodes have high impact on SSV and FT, but have no effect on decolorization and COD removal. Optimum condition was initial pH of 7.43, current density of 5 mA/cm2 and electrodes distance of 0.5 cm, which SSV, decolorization and COD removal were 1.72 cm/min, 83.78 and 35.48%, respectively.