Synergistic photodegradation of pulp and paper mill wastewater by combined advanced oxidation process

The photodegradation of pulp and paper mill wastewater via the combined advanced oxidation process (solar/Fe²⁺/TiO₂/H₂O₂) has been investigated in a laboratory scale reactor. Central composite design (CCD) was used to evaluate the effect of four operational parameters,i.e., pH, Fe²⁺, TiO₂ and H₂O_2, on the basis of chemical oxygen demand and colour removal and the optimum conditions were found to be at pH = 7, Fe²⁺ = 0.10 g/L, TiO₂ = 0.13 g/L and H₂O₂ = 1.80 mL/L. The experimental responses of 98% COD and colour removal were observed at 75 min of treatment, with a significant increase in biodegradability from 0.22 to 0.60 at 45 min of treatment. The combined process followed the first order reaction, with a reaction rate constant of 0.0537 min^–1, which was 2.70 times and 3.38 times more effective than the solar photo-Fenton and solar photocatalytic processes respectively. A synergetic effect of 1.50 and synergetic biodegradability of 0.80 were exhibited in the combined process. The results showed that the combined process were more economically feasible than the solar photo-Fenton and solar photocatalytic processes. Under optimum conditions, an overall treatment cost of 14 US$/m³ of the combined process per day was calculated.