Ozone and ozone/vacuum-UV degradation of diethyl dithiocarbamate collector: kinetics, mineralization, byproducts and pathways.

The diethyl dithiocarbamate (DDC) collector, a precursor of toxic -nitrosamines, is detected in flotation wastewaters usually at the ppm level. In this study, the O and O/Vacuum-UV (O/VUV) processes were compared to investigate the efficient removal of DDC with a low risk of -nitrosamine formation. The results showed that 99.55% of DDC was removed at 20 min by O/VUV, and the degradation rate constant was 3.99 times higher than that using O-alone. The C, S and N mineralization extents of DDC using O/VUV reached 36.36%, 62.69% and 79.76% at 90 min, respectively. O/VUV achieved a much higher mineralization extent of DDC than O-alone. After 90 min of degradation, O/VUV achieved lower residual concentrations of CS and HS, and released lower amounts of gaseous sulfur byproducts compared to O-alone. The solid phase extraction and gas chromatography-mass spectrometry (SPE/GC-MS) analysis indicated that the main byproducts in O/VUV degradation of DDC were amide compounds without the detection of -nitrosamines. The avoidance of -nitrosamine formation might be attributed to exposure of UV irradiation and enhanced formation of ˙OH radicals in the O/VUV system. The degradation pathways of DDC were proposed. This work indicated that O/VUV was an efficient alternative treatment technique for the removal of DDC flotation collector with low risk of -nitrosamine formation.