Treatment of dinitrodiazophenol industrial wastewater in heat-activated persulfate system.

Heat-activated persulfate oxidation process was investigated as the treatment of dinitrodiazophenol industrial wastewater to degrade refractory pollutants and improve biodegradability. By studying the effects of 4 factors and carrying out orthogonal tests and scale-up experiments, optimal treatment conditions (temperature 90 °C, reaction time 75 min, PS dosage 20.0 g L-1 and initial pH ∼2.0) were obtained. The results showed that under these conditions, COD and color removal efficiencies were 99.22% and 99.99%, respectively. Moreover, an increase in BOD5/COD ratio (from 0 to 0.31) indicates significantly improved biodegradability. Dinitrodiazophenol dosage was measured by high performance liquid chromatography, which showed that dinitrodiazophenol removal efficiency reached 99.99%. Furthermore, the degradation process was analyzed by ultraviolet-visible spectra and Fourier transform infrared spectra. The former demonstrated that aromatic compounds in the system were destroyed during mineralization and the latter indicated that nitro groups on the benzene ring could be oxidized to nitrate. After verification test of the free radicals, mechanism of heat-activated persulfate system was assumed to be that SO4˙- and ·OH function together and SO4˙- predominate. To conclude, the heat-activated PS oxidation technology performs effectively in treatment of DDNP wastewater and expands applications of sulfate-radical-based advanced oxidation technology in industrial-wastewater treatment.