Removal of multi-dye wastewater by the novel integrated adsorption and Fenton oxidation process in a fluidized bed reactor

Traditionally, a few processes have to be employed in sequence for multi-dye removal, due to the different physical and chemical characteristics of the dyes. In this study, we innovatively developed an integrated adsorption and Fenton oxidation fluidized bed reactor (FBR) based on the hydraulic classification theory, which could efficiently remove dispersed red, acid yellow, and reactive brilliant dyes. The fluidized solids such as ceramsite and activated carbon could be separately fluidized at the bottom and the top part of the FBR, respectively. As a result, Fenton oxidization of dyes was promoted by the fluidization of ceramsite and activated carbon. Besides, adsorption of activated carbon could synergistically act on the dyes. The results showed that the removal efficiencies of acid yellow 2G, disperse red 60, and reactive brilliant blue X-BR could reach 100, 79.8, and 84.9 % in 10 min, respectively. Lots of intermediates with unsaturated bonds were generated during Fenton reaction, which was further removed by adsorption of activated carbon. Consequently, a high COD removal of 93 % was obtained. Interestingly, some of Fe³⁺ produced during Fenton reaction was further precipitated and crystallized as FeO(OH) or Fe(OH)₃ on the surface of activated carbon and ceramsite, which could be potentially recycled for further utilization as a heterogeneous catalyst. Meanwhile, the other Fe³⁺ might be removed in the form of ferro-organic complexes by adsorption onto the activated carbon. Thus, only a little iron hydroxide sludge was generated in the FBR. This novel FBR gave us an effective clue to realize multi-reactions for textile wastewater treatment by employing hydraulic classification fluidization.