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Title: Light Emitting Diode Based Photochemical Treatment of Contaminants in Aqueous Phase
Author: Yu, Linlong
Advisor: Achari, Gopal
Langford, Cooper
Keywords: Engineering--Civil;Engineering--Environmental
Issue Date: 28-Apr-2014
Abstract: In this research, photochemical treatment of pesticides and polychlorinated biphenyls (PCBs) in aqueous medium were investigated. The studies on photochemical treatment of these two groups of compounds, along with radiation field modelling, further, led to the design of an efficient light emitting diode (LED) based flow-through photocatalytic reactor. Sensitized photodechlorination of PCBs in surfactant solutions was studied. Three types of surfactants at different concentrations were investigated. The neutral and cationic surfactants were found to be more effective than the anionic one. In each case the surfactant concentration was found to play a significant role in the rate of dechlorination. LED based photocatalytic degradation of pesticides and chlorophenols, namely 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA) , 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) was studied. Further, the impact of photocatalyst loading and light intensity on the degradation rate was evaluated. The degradation of 2,4-D under LED irradiation was compared to that with mercury discharge lamp irradiation. The results show these compounds can be efficiently degraded using LED based TiO2 photocatalysis. They are completely mineralized upon prolonged irradiation. Our results indicate that LEDs are a better light source than the mercury lamps. To design an efficient LED based photocatalytic reactor, a radiation field model was developed in this research. The model was tested with experimental data and good agreement between two was noted. The model can be used to optimize the photoreactor and chose the optimal gap between adjacent LEDs, the irradiated distance and the light output of LEDs for a homogenous radiation field. Finally, an LED based photocatalytic reactor was designed and fabricated. The reactor uses anodized TiO2 nanostructure as a photocatalyst. The performance of reactor was evaluated and optimized by studying the degradation of 2,4-D. The effect of different operational parameters on the reactor performance were investigated, including light intensity, distance between the LED module and photocatalytic plate (DL-P), the flow rate through the reactor, presence of external electron scavengers and photocatalyst configuration. A power law relationship was observed between the light intensity (2.2 mW cm-2~17.3 mW cm-2) and the first order degradation rate constant for 2,4-D. A suitable flow rate and D(L-P) was determined for the reactor. Enhanced performance of the reactor was observed where electron scavengers were introduced.
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