Simple effective new bio-adsorbents for the removal of highly toxic nitrite ions from wastewater

Bio-adsorbents derived from Sesbania grandiflora (SGSP/SGSAC) and Amorphophallus paeoniifolius (APSP/APSAC) plants are investigated for their ability to remove nitrite from polluted water. Different extraction conditions have been investigated and optimized for the maximum nitrite removal. Adsorption capacities are found to be 44.5 mg/g for SGSP, 57.5 mg/g for SGSAC, 40.0 mg/g for APSP and 65.5 mg/g for APSAC. Thermodynamic parameters are evaluated. High values of ΔH° for SGSAC (50.872 kJ/mole) and APSAC (67.907 kJ/mole) indicate ion exchange mode of sorption. Spontaneous and endothermic nature of sorption is indicated by negative ΔG values. Positive values of ΔS emphasizes the disorder at solid/liquid interface. The adsorption follows Langmuir isotherm for all the four sorbents, indicating formation of monolayer of nitrite ‘onto’ the surface of sorbents and uniform distribution active sites. Pseudo second-order kinetics explains well the kinetics of adsorption and this reflects that the adsorption is through exchange of electrons or sharing of electrons between nitrite and functional groups sorbents. The developed sorbents are applied effectively for nitrite removal from polluted lake real water samples. The merit of the present investigation is that simple, effective and easily available plant-based bio-materials are identified for the removal of toxic nitrites from water.