Treatment of textile wastewater by SCWO in a tube reactor

Oxidation of aqueous solutions of a model azo dye pollutant (CI Disperse Orange 25) was studied in a continuous flow reactor, operated at temperatures between 400 and 600 °C and at a fixed pressure of 25 MPa. The parameters used were the temperature, dye concentration, oxidant concentration and flow rate. The initial dye concentrations were in the range of 24.25 × 10^-3 and 121.25 × 10^-3 mol L^-1 in terms of chemical oxygen demand (COD). Hydrogen peroxide (H₂O₂) was used as a source of oxygen, and the initial oxidant concentrations were between 36.75 × 10^-3 and 183.75 × 10^-3 mol L^-1. The results demonstrated that the supercritical water oxidation (SCWO) process decreases the chemical oxygen demand up to 98.52% in very short reaction times (at a residence time of 4-12 s). Global rate expression according to wastewater and oxidant concentration was regressed from the complete set of data. The first-order global rate expression was determined with an activation energy of 27.8(±1.2) kJ mol^-1 and a pre-exponential factor of 34.3(±1.5) s^-1 to a 95% confidence level.