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 wastewater from explosives production containing dinitrodiazophenol (DDNP). The 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−1 min−1) and a higher chemical oxygen demand reduction (76.16%) compared to other controlled processes under the optimized conditions of initial pH = 3.0, PS dosage = 6 g L−1, FeS dosage = 0.4 g L−1, 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 wastewater from explosives production 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 and adsorption aperture, and stronger magnetism, which enhanced the treatment efficiency of 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 is a highly efficient method for treating wastewater from explosives production.