Bacteria immobilization on neem leaves/MnFe2O4 composite surface for removal of As(III) and As(V) from wastewater

Selected bacterial strain Corynebacterium glutamicum MTCC 2745 was immobilized on the surface of neem leaves/MnFe2O4 composite (NL/MnFe2O4 composite). The uptake of the biosorbent in combination with the bacterial strain to act as arsenic scavengers from synthetically prepared wastewater was evaluated. The influence of contact time and temperature on the removal of both As(III) and As(V) was investigated. The effect of temperature and initial concentration on the adsorption kinetics was also examined. The equilibrium was achieved after about 240 min at a temperature of 30 °C. Nonlinear regression analysis was done for determining the best-fit kinetic model on the basis of three correlation coefficients and three error functions and also for predicting the parameters involved in kinetic models. The results showed that Fractal-like mixed 1, 2 order model for As(III) and Brouser–Weron–Sototlongo as well as Fractal-like pseudo second order models for As(V) were capable to deliver realistic explanation of biosorption/bioaccumulation kinetic. The adsorption kinetics data also followed pseudo second order kinetic model proposing chemisorption nature of the process. Intraparticle diffusion model confirmed that intraparticle was not a fully operative mechanism. Applicability of various mechanistic models in the present study showed that the rate controlling step in the biosorption/bioaccumulation of both As(III) and As(V) was film diffusion rather than intraparticle diffusion. The estimated thermodynamic parameters ΔG0, ΔH0 and ΔS0 exposed that biosorption/bioaccumulation of both As(III) and As(V) was feasible, spontaneous and exothermic under studied conditions. The activation energy (Ea) calculated from Arrhenius equation indicated the nature of biosorption/bioaccumulation being ion exchange type. Increasing concentration of As(III) and As(V) furthermore improved the initial sorption rate h, from 3.91 to 343.54 mg/g min and 4.3 to 550.67 mg/g min, respectively. Spectroscopic studies (Fe-SEM and FT-IR) confirmed that ion exchange process was responsible for the uptake of arsenic (As(III) or As(V)) onto immobilized cells.