Comparative Evaluation of Low- and Medium-Pressure UV Lamps for Photo-degradation of RDX Wastewater

RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) is a highly toxic heterocyclic nitramine compound which enters the environment during manufacturing, disposal, or military training activities. This study aimed to evaluate the effectiveness of different treatment methods, including direct photolysis, photo-peroxidation, and the photo-Fenton oxidation, using low- and medium-pressure UV lamps for the degradation of RDX wastewater. Rate of degradation and mineralization of RDX, COD reduction, and nitrate content were compared for all these processes. In terms of RDX degradation, the study found that direct photolysis with 125-W medium-pressure UV lamp resulted in 71% removal rate. In contrast, the low-pressure UV lamp of 16 W intensity only showed removal rate of 35%. When comparing the UV/H2O2 process to direct photolysis, it was found that the degradation rate of RDX increased for both low- and medium-pressure systems. Among the different advanced oxidation processes evaluated, the photo-Fenton oxidation process resulted in the highest degradation of RDX compared to direct photolysis and photo-peroxidation processes. Specifically, the addition of 10 mL of Fenton's reagent at a ratio of 1:3 (H2O2:Fe2+) resulted in 98% and 57% removal of RDX within 60 min of irradiation time for the medium-pressure and low-pressure UV lamps, respectively. The highest levels of mineralization for RDX in terms of COD and nitrate removal, amounting to 90% and 42%, respectively were obtained using photo-Fenton oxidation in 60 min of treatment time.