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.
Highlights
Confectionery wastewater effluents contain high amounts of sugar, sugar alcohol, artificial sweeteners, food additives, colorants (TiO2 ), natural flavors, and artificial flavors that account for their high strength in chemical oxygen demand (COD)and biological oxygen demand (BOD) [1,2]
The study conducted by Sang et al showed promising efficiency of TiO2 in degrading the artificial sweeteners found in confectionery wastewater and in mineralizing the intermediate products generated during the degradation process [4]
The statistical model developed through response surface methodology (RSM) combined with a four-factor Box-Behnken design (BBD)
Summary
Confectionery wastewater effluents contain high amounts of sugar (sucrose), sugar alcohol, artificial sweeteners (aspartame, acesulfame, and sucralose), food additives, colorants (TiO2 ), natural flavors, and artificial flavors that account for their high strength in chemical oxygen demand (COD)and biological oxygen demand (BOD) [1,2]. Confectionery wastewater effluents contain high amounts of sugar (sucrose), sugar alcohol, artificial sweeteners (aspartame, acesulfame, and sucralose), food additives, colorants (TiO2 ), natural flavors, and artificial flavors that account for their high strength in chemical oxygen demand (COD). Artificial sweeteners, such as aspartame, acesulfame, and sucralose, are extremely stable throughout the conventional wastewater treatment processes; toxicity will increase after photodegradation [4,5,6]. Advanced oxidation processes (AOPs) are promising and environmentally friendly wastewater treatment technologies capable of mineralizing deleterious substances in wastewater systems [4,8,9,10]. The study conducted by Sang et al showed promising efficiency of TiO2 in degrading the artificial sweeteners found in confectionery wastewater and in mineralizing the intermediate products generated during the degradation process [4]. Modifications of TiO2 photocatalysts through metal doping, non-metal doping, and its combination with another semiconductor photocatalyst are common methods to extend the absorption wavelength of TiO2 towards visible light spectrum, to restrict the recombination of electron-hole pairs, and to increase the specific surface area of the photocatalyst [9,10,11,12,13,14,15,16,17]
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