Abstract
An alternative process for the removal of organic pollutants in aqueous systems is photocatalysis. The challenges hindering its industrial use are electron-hole recombination and mass-transfer limitations. In order to address these problems, the objective of this study is to introduce air by sparging, and design an air-sparged photocatalytic reactor using titanium dioxide immobilized on borosilicate glass. The performance of the reactor on the removal of the model pollutant, methylene blue (MB), was evaluated and compared against the reactor operated without sparging. The effect of mass-transfer limitations on reactor performance was also investigated by regression using a Langmuir-type model equation. The sparged photocatalytic reactor was able to degrade 57% MB in 2 hours, an improvement of 40% compared to no sparging, and is comparable to similar reactors in literature, but with the advantage of using less expensive materials of construction and simpler immobilization technique. Mass-transfer limitation studies showed a good fitting of the initial reaction rate r , with r = 0.1399 Q / (0.6120 + Q ) for the sparged operation, and Q is the volumetric flowrate of water (L/min). The model also shows that the reactor operates near the reaction-limited regime, and that the extent of mass-transfer limitation effects was reduced by the present reactor.
Highlights
The development of advanced wastewater treatment processes has been well studied over the years in light of the detrimental effects of water pollution, organic compounds coming from industrial effluents
Adsorption processes have a problem with the disposal of spent adsorbent; chemical treatment processes may cause the formation of harmful byproducts; and biological processes are feasible only for contaminants that are not toxic to the microbes present in the system
The performance of the reactor, measured as percent removal of methylene blue (MB), under sparged and nonsparged operation was compared at the following process parameters: 2.69 ppm initial MB concentration, pH 7, 2.8 liters per minute (L/min) water flowrate [17], and 2.0 L/min air sparging rate, at 30, 60, 90 and 120 minutes
Summary
The development of advanced wastewater treatment processes has been well studied over the years in light of the detrimental effects of water pollution, organic compounds coming from industrial effluents These treatment processes are classified under physical, chemical or biological [1, 2]. Adsorption processes have a problem with the disposal of spent adsorbent; chemical treatment processes may cause the formation of harmful byproducts; and biological processes are feasible only for contaminants that are not toxic to the microbes present in the system An alternative to these processes is photocatalysis, which uses ultraviolet or visible light to initiate the degradation of organic pollutants using a photocatalyst, resulting to complete mineralization [2,3,4,5]. Photocatalysis offers an alternative because the degradation of pollutants is complete – there are no unwanted byproducts; there is no transfer of pollutants from one phase to another; and its application is a wide range of pollutants
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