Potential of Luffa cylindrica seed as coagulation-flocculation (CF) agent for the treatment of dye wastewater: Kinetic, mass transfer, optimization and CF adsorption studies

Abstract

Background: In dye-based wastewater decontamination, coagulation-flocculation (CF) induced by Luffa cylindrica seed (LCS) was applied. Methods: The effects of parameters (dosage, pH, stirring/settling time) were investigated using one-factor-at-a-time and Box-Behnken jar test which was designed to optimize the removal of color/total suspended solids (CTSS), chemical oxygen demand (COD) and Chromium VI metal. Proximate and instrumental LCS and post-treatment settled sludge characterization, kinetics, mass transfer and CF adsorption study of the process were investigated. Significant findings: LCS's proximate composition revealed high crude protein, while its instrumental characterization identified a network of structures with an active surface and a partial crystalline composition. At pH 2, the removal efficiency of CTSS was 99.2% at 1400 mg/L for 30mins, COD was 90.07% at 1400 mg/L for 30mins and at pH 6 chromium was 98.29% at 1800 mg/L for 15mins, these were reported at optimum conditions. Kinetic parameters; rate constant, K11, and half-time coagulation, τ1/2 were determined. The CF adsorption isotherm followed the Freundlich pattern and the kinetic was pseudo-second order. After settling for 300 min, dye removal decreased from the original dye concentration of 1000mgL-1 to 3mgL-1 due to the rapid mass transfer process. R2 was > 0.9 for all the studies, and error indicators reported low values. The high dye-polluted wastewater decontamination potential of bio-coagulant was therefore established. The kinetic, mass transfer and CF adsorption study data obtained may be useful for bio-coagulation system design, a start-up operating time, design control and optimization.

Keywords

• Dye wastewater
• Luffa cylindrica seed
• Coagulation-flocculation
• Box-Behnken design
• CF adsorption study