Effect of chemical structures of reactive dyes on color removal by an anaerobic-aerobic process

An Anaerobic/Aerobic SBR system was used to treat a synthetic wastewater with glucose and acetic acid (1000 mg/l COD) as carbon sources together with 20 and 100 mg/l of four different reactive dyes: disazo vinylsulphonyl, anthraquinone vinylsulphonyl, anthraquinone monochlorotriazinyle and oxazine. The decolorization efficiencies of the first three dyes at the 20 mg/l dye concentration were 63, 64 and 66%, respectively, and at the 100 mg/l dye concentration were 58, 32 and 41%, respectively. For the disazo dye, two color removal rates were evident, with the initial rate in the first two hours of the anaerobic stage higher than the latter. For the two anthraquinone dyes, only one rate of color removal was seen. For the oxazine dye, a high decolorization was observed in the reactor, but when disturbed, the color re-appeared for unexplainable reasons. The phosphorus removal efficiencies were 78, 52, 41 and 96% for the four dyes of 20 mg/l, respectively, while the corresponding numbers for the 100 mg/lcondition were 48, 48, 48 and 42%, respectively, and different types of dyes had different impacts on the phosphorus removal performance. COD and TKN removals were very high, i.e., 90–99 percent. The disazo reactive dye was decolorized by the reductive reaction, which resulted in the cleavage of the azo bond. Meanwhile, the decolorization of anthraquinone dyes is believed to be through the direct adsorption of dyes on to the floc materials.