Photocatalytic treatment of an actual confectionery wastewater using Ag/TiO2/Fe2O3: Optimization of photocatalytic reactions using surface response methodology

Abstract

Titanium dioxide (TiO2) photocatalysis is one of the most commonly studied advanced oxidation processes (AOPs) for the mineralization of deleterious and recalcitrant compounds present in wastewater as it is stable, inexpensive, and effective. Out of all, doping with metal and non-metals, and the heterojunction with another semiconductor were proven to be efficient methods in enhancing the degradation of organic pollutants under ultraviolet (UV) and visible light. However, complex degradation processes in the treatment of an actual wastewater are difficult to model and optimize. In the present study, the application of a modified photocatalyst, Ag/TiO2/Fe2O3, for the degradation of an actual confectionery wastewater was investigated. Factorial studies and statistical design of experiments using the Box-Behnken method along with response surface methodology (RSM) were employed to identify the individual and cross-factor effects of independent parameters, including light wavelength (nm), photocatalyst concentration (g/L), initial pH, and initial total organic carbon (TOC) concentration (g/L). The maximum TOC removal at optimum conditions of light wavelength (254 nm), pH (4.68), photocatalyst dosage (480 mg/L), and initial TOC concentration (11,126.5 mg/L) was determined through the numerical optimization method (9.78%) and validated with experimental data (9.42%). Finally, the first-order rate constant with respect to TOC was found to be 0.0005 min−1 with a residual value of 0.998.