Decomposition and mineralization of sulfaquinoxaline sodium during UV/H2O2 oxidation processes

• Sulfaquinoxaline sodium (SQ-Na) was completely decomposed in UV/H2O2 process.
• 30% of total organic carbon was removed after SQ-Na was completely decomposed.
• Decomposition of SQ-Na by UV/H2O2 fitted fluence-based pseudo-first-order kinetics.
• Possible decomposition pathways of SQ-Na by UV/H2O2 process were proposed.

Sulfaquinoxaline sodium (N′1-quinoxalin-2-ylsulphanilamide sodium, SQ-Na) has been widely used to prevent coccidiosis in poultry, swine, and sheep. The quinoxaline group within SQ-Na exhibits mutagenic and carcinogenic properties. The removal of residual SQ-Na from wastewater has not been reported before. In this study, the decomposition of SQ-Na in aqueous solutions in UV/H2O2 oxidation process was investigated. The results show that SQ-Na was completely decomposed during UV/H2O2 oxidation process, and the process fitted a fluence-based pseudo-first-order kinetics model when the initial H2O2 concentration varied from 0 to 160 mg/L with rate constant of kobs = 0.802 × [H2O2] + 0.206 × 10−3, (R2 = 0.990). The decomposition of SQ-Na via UV/H2O2 process was favorable under acidic and neutral conditions but was inhibited under strong alkaline conditions (pH ⩾ 11). The presence of bicarbonate, chloride and nitrate ions were shown to have slight inhibition on the decomposition, but humic acids significantly decreased the decomposition rate. As compared with in deionized water, the decomposition rate of SQ-Na in surface water and wastewater treatment plant (WWTP) effluent was significantly decreased at 80 mg/L of H2O2, but the decrease was mitigated with more H2O2 addition. The decomposition products of SQ-Na were identified using ion chromatography and liquid chromatography with an ion trap and time-of-flight mass spectrometry (LCMS-IT-TOF). Based on these decomposition products, the possible decomposition pathways of SQ-Na in the UV/H2O2 oxidation process were proposed.

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