Activation of persulfate by microwave radiation combined with FeS for treatment of wastewater from explosives production
A persulfate (PS) process activated by microwave (MW) radiation and combined with FeS (MW-FeS/PS) was developed to treat explosive production wastewater containing dinitrodiazophenol (DDNP). Treatment efficacy and degradation characteristics of refractory organics in the wastewater and the improvement in biodegradability were studied. The catalytic capacity of FeS was determined and the electrical energy consumption of the MW-FeS/PS process was evaluated. The MW-FeS/PS process exhibited a more rapid reaction rate (0.208 mg/(L·min)) and higher chemical oxygen demand reduction (76.16%) compared to other controlled processes under optimized conditions of initial pH 3.0, PS dosage 6 g/L, FeS dosage 0.4 g/L, MW power 450 W, and reaction time 16 min. Additionally, biodegradability was greatly improved from an initial value of 0.040 for raw wastewater to 0.487 for treated wastewater. Spectral analysis indicated that benzene-ring substances, nitro group substances, and diazo group substances in the explosive production wastewater containing DDNP were considerably degraded by the MW-FeS/PS process. After several operation cycles, FeS maintained high catalytic capacity. After reaction, the used FeS showed a larger specific surface area, adsorption aperture, and stronger magnetism, which enhanced treatment efficiency for the MW-FeS/PS process and facilitated separation of the catalyst from the wastewater. Radical quenching experiments showed that sulfate radicals and hydroxyl radicals both considerably contributed to organics degradation in the MW-FeS/PS process. In addition, the MW-FeS/PS process consumed less energy than other processes and achieved higher treatment efficacy, confirming that the MW-FeS/PS process was a highly efficient method for treating explosive production wastewater.