Use of Plantago major L. as a natural coagulant for optimized decolorization of dye-containing wastewater

• A new natural coagulant for wastewater treatment was introduced.
• The treatment process was optimized by Box–Behnken response surface design.
• Effect of time, pH and coagulant dose on the color and COD reduction were analyzed.
• Coagulation mechanisms include charge neutralization and adsorption.

In this study, Plantago major L. has been evaluated as an active natural coagulant for the removal of dye from a model textile wastewater containing neutral red. Response surface methodology (RSM) based on a three-variable, three-level Box–Behnken design (BBD) was employed to study and optimize the treatment process. The effect of three parameters including contact time, pH and the coagulant dose on the color and COD reduction were analyzed. A partial cubic equation could accurately model the response surface with an R2 of 0.99. The pH was found to be the most significant parameter affecting both color and COD reduction. A high color (92.4%) and COD (81.6%) reduction efficiency was obtained using P. major L. at the optimal conditions of 49.6 min, pH 6.5 and 297.6 mg/L coagulant dose. The results also showed that the isothermal equilibrium could be represented by the Freundlich model with an R2 of 0.94.

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