Degradation of residual BK809 in flotation wastewater by ozonation

Ozonation was used to degrade residual BK809 in flotation wastewater and the degraded products in different stages were identified and quantified by gas chromatography-mass spectrometry(GC-MS).The results showed that the COD removal rate of 68.68% could achieve at an ozone flow rate of 300mg·h^-1 for 20min and pH 9-11.It was indicated from GC-MS analysis that BK809 was firstly oxidized to azobenzene and then converted to nitrobenzene.With the deepening of ozonation,the benzene was broken and further decomposed into C₁₅-C₂₅ carbon-chain alkanes and gaseous substances,including nitrogen oxides and carbon oxides.Finally the residual mass percentage of total organic compounds(TOC) reduced from 100.00% to 17.18%.Meantime,the chroma of the wastewater increased from 5.02 to 471.71 and then decreased to 28.75;in macroscopic view,the color of the wastewater turned from colorless to brown,and then from brown to milky.