Methylene Blue Bleaching by a Solar-Driven Advanced Oxidation Process

摘要

Organic dyes are one of the common contaminants in industrial wastewaters. Color removal is always one of the challenges during the treatment of dye wastewaters. Ultraviolet light (UV)- based Advanced Oxidation Processes (AOPs) have been developed for decolourization of dye wastewater; however, the application cost is usually high because it often involves the use of intensive energy for the UV system. Instead, this research investigated the possible application of a sunlight-driven AOP for the decolorization of dye wastewaters. This study takes advantage of the overlap between the absorption spectrum of the hypochlorite ion (OCl~-) and the UV region of solar spectrum as the initiator of the UV/chlorine AOP. Methylene blue (MB) was selected as a model organic dye for the evaluation of the possibility of the photobleaching by this solar-driven AOP. This research demonstrated that photobleaching of MB occurs with the UV/chlorine AOP at 303 nm and pH 10 in bench-scale experiments; the MB photobleaching reaction obeyed a pseudo first-order rate law. The bleaching rate constant for a specific concentration of MB was estimated when the UV was completely absorbed by an infinitely high concentration of OCl~- at 303 nm. By concdutcing the theoretical calculations with the reference spectrum air mass 1.5 from Renewable Resource Data Center, this estimation indicated that less than 6 h of solar exposure would be required for 99 % color removal for the chosen MB mixture.