The treatment of dying wastewater, especially the decoloration of it, remains a difficult task in industrial wastewater treatment. Our previous work reports that a novel method, the UV/acetylacetone (AA) process, is efficient in the decoloration of dyes, especially azo dyes. In this work, the decoloration of an anthraquinone dye with the UV/AA method was systematically investigated with Alizarin Red (AR) as a model compound. The effects of initial solution pH, concentration of AR, and concentration of AA on the decoloration efficiency were studied. The AR concentration used in this work was close to the upper limit of actual dye wastewater. Compared with the well-known UV/H2O2 process, the UV/AA process had much higher decoloration efficiency in the pH range of 3～9 and the decoloration process could be described with the pseudo-first order kinetics. Under identical conditions, the k1 of the UV/AA process was 18 times higher than that of the UV/H2O2 process (0.1312 vs 0.0068 min-1). From pH effect experiments, we found that strongly alkaline condition was adverse to the effectiveness of the decoloration. Based on the pH effects on the forms of AA and the UV-Vis spectra of the solutions, we infer that the enol form of AA played a key role in the degradation of AR. Through TOC (total organic carbon), COD (chemical oxygen demand) and BOD (biochemical oxygen demand) analysis, we found that there was only limited removal of the TOC and COD of the solution after the UV/AA treatment. However, the biodegradability of the solution was significantly improved as the BOD/COD was raised from 0.42 to 0.70. This result suggests that the UV/AA process might be used as a pretreatment step in sequential chemical-biological treatment, which provides a new idea for the use of small molecular diketones in wastewater treatment. Interestingly, in the UV/AA process, the decoloration of azo dyes was found to be insensitive to dissolved oxygen, whereas for the decoloration of AR, dissolved oxygen played a crucial role. These results demonstrate that the mechanisms in the UV/AA process for the decoloration of variant types of dyes might be different. Therefore, a quantitative structure-activity relationship is warranted for the better understanding of the UV/AA process.
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