Combined use of O3/H2O2 and O3/Mn2+ in flotation of dairy wastewater

Abstract

This work investigated the degradation of organic matter present in synthetic dairy wastewater by the combination of ozonation (ozone (O₃)/hydrogen peroxide (H₂O₂)) and catalytic ozonation (ozone (O₃)/manganese (Mn²⁺)) associated with dispersed air flotation process. The effect of independent factors such as O₃ concentration, pH and H₂O₂ and Mn²⁺ concentration was evaluated. For the flotation/O₃/H₂O₂ treatment, the significant variables  (p ≤ 0.05) were: O₃ concentration (linear and quadratic effect), H₂O₂ concentration linear and quadratic effect, pH values (linear and quadratic effect) and interaction O₃ concentration versus pH. For catalytic ozonation, it was observed that the significant variable was the linear effect of O₃ concentration. According to the desirability function, it was concluded that the optimal condition for the treatment of flotation/O₃/H₂O₂ can be obtained in acidic solution using O₃ concentrations greater than 42.9 mg L^-1 combined with higher concentrations of H₂O₂ to 1071.5 mg L^-1. On other hand, at pH values higher than 9.0, the addition of O₃ may be neglected when using higher concentrations than 1071.5 mg L^-1 of H₂O₂. For flotation/ozonation catalyzed by Mn²⁺, it was observed that metal addition did not affect treatment, resulting in an optimum condition: 53.8 mg L^-1 of O₃ and pH 3.6.