Investigating UDMH degradation using microwave-assisted manganese oxidation: Mechanistic insights, toxicity assessment, and nitrogenous product analysis

The leakage of unsym-dimethylhydrazine (UDMH) wastewater poses a significant threat to environment due to the enormous toxicity of UDMH and its degradation by-products. The toxicity of UDMH wasterwater is mainly due to the toxicity of nitrogen-containing products. Herein, a microwave-assisted manganese trioxide degradation strategy was proposed based on advanced oxidation process (AOPs). Under recommended reaction conditions of UDMH initial concentration 250 mg/L, initial pH of reaction solution 9, microwave power 300 W, Mn 2 O 3 dosage 10 g/L and reaction duration 1 h, a high COD degradation efficiency of 85.81 %, UDMH degradation efficiency of 99.78 % were achieved. Under this condition, the amount of nitrogen-containing products concerned in the experiment was the least. The effective degradation of UDMH and COD was benifitting from the microwave-accelerated molecular vibration and the abundant active substances catalysed by Mn 2 O 3 , especially •OH. Material characterization results indicated that Mn 2 O 3 might play a catalytic role in reaction. The degradation intermediates of UDMH were further identified by solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS), and the reaction mechanism was analyzed to reveal possible degradation pathway of UDMH. Under attack of •OH, UDMH degraded into various intermediates. ECOSAR toxicity assessment software analysis and Selenastrum capricornutum toxicity experiment showed that the toxicity of UDMH decreased significantly after microwave assisted Mn 2 O 3 degradation due to the reduction of electrophilic groups. This work provides an effective method to mitigate ecological environmental harm of UMDH wastewater in practical production.