Removal of microcystin-LR from aqueous solution using Moringa oleifera Lam. seeds

The removal of microcystin-LR from aqueous solution using native Moringa oleifera Lam. seeds powder (MSP) and chemically pretreated M. oleifera Lam. seed powder (PMSP) was investigated in terms of equilibrium and kinetics. Optimum sorption conditions were determined as a function of pH (2-7), adsorbent dosage (0.25-1.0 g/L), initial concentration of microcystin-LR (15-120 mg/L) and contact time (15-360 minutes). The high values of regression constant, 0.98 (MSP) and 0.99 (PMSP), revealed that sorption of microcystin-LR was best fitted by the pseudo second order kinetic model. The equilibrium study was best fitted by the Freundlich model with both the adsorbents. The maximum sorption capacity by MSP and PMSP for microcystin-LR was 85.5 ± 1.1 mg/g and 92.49 ± 2.4 mg/g respectively. Fourier transform infrared spectroscopy showed the major involvement of carboxyl and hydroxyl groups for microcystin-LR sequestration either by complexation or ion exchange mechanism. The contribution of the adsorption phenomenon was confirmed by scanning electron microscopic analysis of microcystin-LR loaded and unloaded PMSP. Thus, the HCl-pretreated M. oleifera Lam. seed powder proved to be the pre-eminent biosorbent for removal of microcystin-LR from the wastewater stream.