Microwave-assisted Fe0-activated persulfate process for treating explosives in production wastewater

Production of dinitrodiazophenol (DDNP) generates a large amount of industrial wastewater that is biotoxic and difficult to treat using traditional methods. In this study, a persulfate (PS) treatment process activated by Fe-0 and assisted by microwave irradiation (MW-Fe-0/PS process) was developed to treat refractory organics in DDNP industrial wastewater. The MW-Fe-0/PS process achieved higher treatment efficiency for the DDNP wastewater than other radiation-assisted and iron-based processes. Increased PS dosage, Fe-0 dosage and MW power enhanced organics removal and significantly accelerated the reaction. However, increasing the initial pH inhibited treatment efficiency. Under optimal treatment conditions (PS = 6 g/L, Fe-0 = 0.4 g/L, MW power = 450 W and initial pH = 3), the biodegradability and efficiencies of removing chemical oxygen demand and total organic carbon reached 0.45, 69.52% and 57.27%, respectively, which are higher than other activation modes (i.e., UV254 44.35% COD removal, US 50.70%, and thermal 53.98%). MW, Fe-0 and PS in combination degraded organics more efficiently than either treatment alone. In addition, nitro-compounds, diazo groups and benzene rings in DDNP industrial wastewater were degraded extensively by SO4 center dot- and (OH)-O-center dot in the process. Iron ions were continuously released by Fe-0, forming a small amount of iron-based (hydrated) oxides on the surface of Fe-0. Thus, Fe-0 maintained high reactivity after repeated use in MW/PS environments. Compared with a similar MW-Fe2+/PS process, the MW-Fe-0/PS process exhibited higher reactivity, longer oxidation effect and higher energy use efficiency due to the slow release of Fe2+ from Fe-0. Therefore, the MW-Fe-0/PS process is an efficient method for treating DDNP industrial wastewater.