Arsenite biosorption from contaminated water using live and dead biomass of marine Lysinibacillus sphaericus strain AsRPSD99: A modeling-based approach

Abstract

Lysinibacillus sphaericus strain AsRPSD99 was isolated from sea sediment and found to be high salt-tolerant (up to 11 % NaCl) and multiple metal-resistant. The AsRPSD99 strain exhibited significant resistance to As(III) (1550 mg·L⁻¹) and As(V) (3500 mg·L⁻¹) and was effective for biosorption of arsenite in both living and dead conditions. Statistical and mathematical methods including central composite design-response surface methodology, kinetic, isotherm, and thermodynamic models have optimized and assessed batch-mode arsenite biosorption mechanisms. As(III) removal varied from 97.6 % to 56.3 % with living biomass and 95.9 % to 54.3 % with dead biomass at the optimal conditions (pH 6.5, temperature 32 °C, NaCl 2 %, agitation 120 rpm) at initial concentrations of 100 to 500 mg·L-1. Maximum As(III) uptake of 281.6 ± 10.4 mg and 271.8 ± 10.3 mg per 1 g of live and dead biomass was achieved at 500 mg·L⁻¹. As(III) biosorption aligns well with Langmuir isotherm (R²: 0.99), pseudo-second-order (R²: 0.96–0.98), and intraparticle diffusion kinetic models (R²: 0.94–0.98), indicating a two-stage monolayer surface chemisorption and intercellular accumulation process. The thermodynamic modeling indicates an endothermic (ΔH^o: +122.02 kJ·mol⁻¹) adsorption mechanism. Fourier transform infrared spectroscopy, field emission scanning electron microscopy with energy-dispersive X-ray analyses, transmission electron microscopy, X-ray diffraction spectroscopy, and X-ray photoelectron spectroscopy confirmed arsenite ion adsorption, ion exchange, and micro-precipitation via cell surface functional ligands. Transmission electron microscopy showed arsenite ions in and around living bacteria. These findings may aid large-scale biomass production and application of AsRPSD99 to treat arsenic-polluted water.