In the present study, the treatment of a typical spent Merox caustic waste (SMC) was investigated by three methods of Fenton-like process, foam fractionation and combination of both methods. Immobilised TiO2/Fe-0 nanoparticles on modified silica nanoparticles were used as heterogeneous Fenton-like catalyst. The characterisation of catalyst was carried out using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), diffuse reflectance spectra (DRS) analysis, thermal gravimetric analysis (TGA), differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The performance of the combined method was evaluated in terms of chemical oxygen demand (COD) residual parameter. The parameters including pH, gas flow rate to the separator column, concentrations of hydrogen peroxide/catalyst/surfactant/chelate agent, surfactant type, and chelate agent type were investigated to obtain the optimum conditions of the process by response surface methodology (RSM) based on eight-factors central composite design (CCD). Under optimum conditions of combining Fenton-like and foam fractionation methods, the minimum residue of COD was 10.98 ppm, corresponding to a COD removal of 99.7%. However, the measured values for the Fenton-like or foam fractionation methods alone did not exceed 88.9% and 58.4%, respectively. In addition, hydrogen peroxide consumption decreased by 63% compared to the Fenton-like method. Also, another important result shows that the use of cationic surfactants is more effective than anionic and amphoteric for wastewater treatment.
