Enzymatic Decolorization of Dye Wastewater and its Effect on Respiration of Activated Sludge

This study investigated the decolorization and detoxification of a dye originating from a feather-dyeing house using the laccase enzyme. Efficient decolorization was achieved under a wide range of environmental conditions, including pH, temperature, enzyme loading, and dye concentration. The decolorization rate reached up to 98% within 10 min when the mediator acetosyringone was present. Decolorization was attributed to the degradation of the dye by laccase, as analyzed using liquid chromatography-mass spectrometry (LC–MS). At least three dominant intermediates (m/z 167.993, 194.475, 118.040) were identified, deriving from the original dye (m/z 521.044). Compared to the non-decolorized dye solution, the decolorized dye ones at various concentrations exhibited lower toxicity towards aerobic activated sludge (AS). This was evident from the significantly higher respiratory intensity of AS, with an O₂ uptake of 35 mg for the decolorized solution versus 11 mg for the non-decolorized solution after 12 h at a 100 mg/L dye concentration. The results suggest that laccase-catalyzed decolorization could serve as an effective pretreatment method for traditional activated sludge (AS)-based processes, thereby enhancing the overall treatment performance of dye wastewater.