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

Abstract

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 Fe0 and assisted by microwave irradiation (MW-Fe0/PS process) was developed to treat refractory organics in DDNP industrial wastewater. The MW-Fe0/PS process achieved higher treatment efficiency for the DDNP wastewater than other radiation-assisted and iron-based processes. Increased PS dosage, Fe0 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, Fe0 = 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, Fe0 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− and OH in the process. Iron ions were continuously released by Fe0, forming a small amount of iron-based (hydrated) oxides on the surface of Fe0. Thus, Fe0 maintained high reactivity after repeated use in MW/PS environments. Compared with a similar MW-Fe2+/PS process, the MW-Fe0/PS process exhibited higher reactivity, longer oxidation effect and higher energy use efficiency due to the slow release of Fe2+ from Fe0. Therefore, the MW-Fe0/PS process is an efficient method for treating DDNP industrial wastewater.