Comparison study on microwave irradiation-activated persulfate and hydrogen peroxide systems in the treatment of dinitrodiazophenol industrial wastewater

Abstract In this study, refractory organics in industrial wastewater containing dinitrodiazophenol (DDNP) were treated by microwave (MW) irradiation-activated persulfate (PS) and hydrogen peroxide (H2O2). The organics degradation effect of MW output power, oxidant dosage and initial pH were investigated. Spectral analysis and radical scavenging experiments were used to investigate the degradation pathway and identify reactive oxygen species in the two systems. As the MW output power increased, kobs of both systems increased, but excessively high-power output inhibited organics degradation in the MW-PS system. The impact of initial pH on MW-PS system performance was not obvious compared to that of the MW-H2O2 system (in which alkalinity significantly limited the reaction with organics). Under the same reaction condition, COD removals reached 89.89% (MW-PS) and 54.56% (MW-H2O2) and biodegradability improved from 0.060 to 0.561 (MW-PS) and 0.535 (MW-H2O2). In addition, SO4·- and ·OH were identified in the MW-PS system but only ·OH existed in the MW-H2O2 system, indicating that the MW-PS system could oxidize more types of organics in DDNP wastewater than the MW-H2O2 system. Furthermore, UV-Vis and FITR analyses showed that organics with diazo groups and nitro-groups could be decomposed and intermediate products with C-O-H (which are biodegradable) will be generated. The MW-PS system also produced a better economic benefit than the MW-H2O2 system. Therefore, this study provides valuable references for the use of MW irradiation-activated oxidants to treat DDNP industrial wastewater.