Application of sonicated chitosan for the remediation of vat dye bath wash: optimization studies using Box–Behnken model

The discharge of industrial effluents into the environment without proper treatment is a major cause of aquatic pollution. One of the massive polluters is the textile dyeing industry, as the wastewater is rich in harmful and complex dyes as well as its undegraded residues. Chitosan was employed as an organic flocculant for the remediation of textile dyes via coagulation-flocculation technique. Wastewater samples were collected from Tamil Nadu Cooperation Textile Processing Mill. The wastewater contained a significant proportion of Vat dye which is used for dying denim materials and cotton fibers. Chitosan was considered due to its ability to the dye moieties and enhance floc formation. The effect of parameters such as chitosan dosage (5–15%V/V), sonication cycle (2–4) and agitation time (30–90 min) was investigated on the remediation process using response surface methodology. Sonication technique was expected to alter the particle size, viscosity and thereby the flocculation efficiency. Three responses namely decolorization (%), residual suspended matter (NTU), and sedimentation rate (cm/sec) were considered as process measuring parameters. Regression analysis showed good fit for the experimental data with correlation coefficient values recorded to be: 0.9931, 0.9465 and 0.9508, respectively. Optimized values reported are chitosan dosage of 15%v/v, sonication cycle 4, and agitation time of 90 min, at which, maximum dye decolorization (60%), and suspended matter reduction (80%) was noted. Thus, chitosan-based flocculant could be a sustainable choice for addressing the issue of textile dye pollution.