Application of zero valent iron (ZVI) immobilized in Ca-Alginate beads for C.I. Reactive Red 195 catalytic degradation in an air lift reactor operated with ozone

Highlights: • ZVI-Alg beads / ozone remove color and mineralize RR195. • The RR195 degradation of by ZVI-Alg beads/O₃ follows a pseudo first order kinetics. • Homogeneous and heterogeneous catalytic ozonation contribute to the degradation of RR195. The efficiency of nanoscale zero-valent iron (nZVI) for the recalcitrant organic pollutants degradation has been frequently reported. However, some disadvantages such as low hydraulic conductivity, rapid passivation and consequent loss of reactivity have motivated researchers to study immobilized forms. In this work, calcium alginate beads incorporated with nZVI were prepared, characterized and applied in a catalytic ozonation system of Reactive Red 195 dye (RR195). In order to avoid shearing the calcium alginate beads, an Air lift reactor operated with Air/O₃ cycles in an 8 mg L⁻¹ concentration was used. The RR195 treatability tests conducted with a dye concentration of 25 mg L⁻¹, 50 g L⁻¹ of nZVI-Alg beads and an Air/O₃ feed flow of 1 L min⁻¹, revealed significant process efficiency, which was not limited only to the dye discoloration. Total discoloration levels were observed in 30 min of treatment and reductions in 97 % of organic matter in 90 min of treatment, measured through the chemical oxygen demand. The typical absorptions of aromatic compounds reduction (λ_max =290 nm) and the acute toxicity reduction (Artemia Saline bioassay), contribute to the Alg-nZVI/O₃ system potential for the application in the treatment of liquid effluents contaminated with dyes.