Treatment of refractory organics in strongly alkaline dinitrodiazophenol wastewater with microwave irradiation-activated persulfate

In this study, persulfate (PS) activated with microwave (MW) irradiation was used to treat strongly alkaline (pH = 12.70–12.80) wastewater containing dinitrodiazophenol (DDNP). The effects of key factors such as the PS dosage, MW output power, influent chemical oxygen demand (COD), and inorganic anions concentration were studied, and the presence of reactive oxygen species was monitored in the MW-PS process. The results showed that at a PS dosage of 6.0 g L−1, MW output power of 750 W, and reaction time of 16 min, the COD was reduced by 74.07% and the color number by 99.40%. In addition, the reaction during the MW-PS process for the treatment of industrial wastewater containing DDNP was comparatively stable and it was relatively unaffected by anions (i.e., chloride, carbonate, nitrate, and bicarbonate ions). Furthermore, SO4·–, OH·, and O2·– jointly degraded organics in the MW-PS process, and O2·– played a vital role in the degradation of organics in the industrial wastewater containing DDNP. Controlled experiments showed that the MW-PS process performed better than MW-H2O2 and ozonation processes in the treatment of alkaline industrial wastewater containing DDNP. Ultraviolet–visible and Fourier transform infrared spectroscopy analyses also indicated that refractory organic compounds with functional groups such as benzene rings, nitro groups (-NO2), and diazo groups (-NN-) were effectively decomposed in the MW-PS process and transformed into intermediate products that contained N–H and –OH. Overall, the MW-PS process was found to be highly effective in the treatment of a strongly alkaline wastewater containing DDNP. [Display omitted] •MW-PS process can degrade refractory organics in strongly alkaline DDNP wastewater.•High degradation capacity and stability was achieved by MW-PS process.•SO4·–, OH·, and O2·– were found to jointly destroy the complex refractory organics.