ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Synergetic effects of mixing parameters, settling characteristics and process kinetics on coagulation treatment of tannery industry wastewater

Magesh Kumar Marichamy and Hawale Pawan Narayan

Department of Chemical Engineering, School of Bio Engineering, SRM Institute of Science and Technology, Kattankulathur, India

E-mail: mmagesh23@gmail.com

Received: 27 October 2021  Accepted: 1 March 2022

Abstract:

The coagulation treatment for the removal of turbidity from tannery industry wastewater using the coagulant protein in Moringa oleifera seeds was investigated in this research work. The natural coagulant was prepared from the seed powder using NaCl and KCl salt solutions each having a concentration of 0.25 M. The effect of coagulant dosage and initial pH on % turbidity removal was investigated for both coagulants. A higher turbidity removal efficiency of 74.11% was achieved with NaCl extracted coagulant at an optimum coagulant dosage of 30 mL and initial pH 9, whereas the coagulant prepared by KCl salt solution exhibited a lower treatment efficiency of 68.52%. The maximum and minimum velocity gradients attained was 1098.8 s⁻¹ at 31 °C and 257 s⁻¹ at 25 °C, respectively. The least residual turbidity was achieved at 440 rpm impeller speed. The relationship between power function and Reynolds number (Re) for unbaffled tank shows that transition zone develops between 30,500 < Re < 56,000. The residual turbidity concentration decreases with increase in settling velocity for different coagulant dosages. The turbidity removal process follows the second-order kinetics model with a rate constant of 0.000158 (mg/500 mL)⁻¹ min⁻¹. The variation of coagulation rate constant with temperature was supported by Arrhenius law (R² = 0.9645) rather than Transition state theory (R² = 0.96) and Collision theory (R² = 0.9624). The exponential decay of concentration ratio with time indicates that Smoluchowski rate equation explains the growth of floc particles governed by fluid motion. This study reveals the successive and optimistic influence of coagulant dose, pH, mixing dynamics, settling mechanism and coagulation rate on turbidity removal from tannery wastewater.

Graphical abstract

Keywords: Green coagulant; Kinetic models; Power number; Arrhenius law; Smoluchowski equation

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-022-02156-6

Chemical Papers 76 (7) 4169–4188 (2022)