Okara and okara modified and functionalized with iron oxide nanoparticles for the removal of Microcystis aeruginosa and cyanotoxin.

Eutrophicating compounds promote the growth of cyanobacteria, which has the potential of releasing toxic compounds. Alternative raw materials, such as residues, have been used in efficient adsorption systems in water treatment. The aim of the present study was to apply the residue Okara in its original form and modified by hydrolysis with immobilization of magnetic nanoparticles as an adsorbent. For the removal, the cyanobacteria Microcystis aeruginosa was chosen, as well as its secondary metabolites, L-amino acids leucine and arginine (MC-LR microcystin), from aqueous solutions. The adsorbents presented a negative surface charge, and the x-ray diffraction (DRX) outcomes successfully demonstrated the immobilization of iron oxide nanoparticles on the adsorbents. The adsorbent with the best result was the Okara hydrolyzed and functionalized with iron oxide, which showed a 47% (qe = 804.166 cel/g) and 85% (qe = 116.94 µg/L) removal for the cyanobacteria cells and chlorophyll-a, respectively. The kinetics study demonstrated a pseudo-first-order adsorption with maximal adsorption in 480 minutes, removing 761 µg/L of chlorophyll-a. In this trial, a low organic material removal has occurred, with a removal rate of 5% (qe = 0.024 mg/g) in the analysis of compounds in absorbance by ultraviolet light (UV) monitored by optical density determination in 254 nm (OD254). Nevertheless, the reaction system with the presence of organic material removed 53,28% of the MC-LR toxin, with adsorption capacities of 2.84 µg/L in a preliminary trial conducted for two hours, arising as a potential and alternative adsorbent with a capacity of removing cyanobacteria and cyanotoxin cells simultaneously.