Biological decolorization and detoxification of malachite green from aqueous solution by Dietzia maris NIT-D

Abstract

Liquid phase adsorptive removal of Malachite Green (MG) by an emerging Dietzia species has been investigated in the present study. Crucial operating parameters were screened and optimized by Plackeet–Burman (PB) and Central Composite Design (CCD), respectively, in batch study considering decolorizing efficiency as response. Results showed that initial dye concentration and initial pH of the system played major role in MG removal and about 72.05% removal was achieved at initial MG concentration of 15mgl−1, initial pH 7.0, inoculum size of 2%(v/v) and nitrogen source of 0.5% (w/v). Fourier Transform Infrared Spectroscopy (FT-IR) and Field Emission Scanning Electron Microscopy (FE-SEM) revealed possible involvement of intracellular protein and surface groups viz. amine (−NH2) and nitro (−NO) in bacterial chemisorptive behavior. Detailed kinetic and equilibrium studies indicated that the process followed pseudo second order reaction kinetics (R2 > 0.999) and Langmuir adsorption isotherm model (R2: 0.998) respectively. Activation energy (Ea) was calculated to be 63.35kJmol−1, Gibbs free energy change(ΔGo) as −2.186kJmol−1 at 37 °C Enthalpy change (ΔHO) as 49.36kJmol−1 and Entropy change (ΔSO) as 166.17Jmol−1K−1 which revealed that the removal process was spontaneous and endothermic in nature. Apparent half saturation constant (Km) and maximum substrate consumption rate (Vmax) was found to be 1317.5mgl−1 and 166.67mgMGgcell−1h−1 respectively. To assess large scale removal prospect, continuous column study was done with whole cell immobilized alginate beads as packing material for the column. 50.15% MG removal was achieved at a continuous flow rate of 1.5mlmin−1. Phytotoxicity and cytotoxicity study revealed that MG treated with Dietzia maris NIT-D are significantly less toxic than its native form in terms of environmental and agricultural aspect.