Treatment Of Explosive Wastewater Using US-Fenton Process

Explosive wastewater generated from manufacturing, transporting, and demilitarizationin explosive industry and army ammunition plants contains rather complex chemicals, whichis toxic and harmful to both human beings and enviroment. Conventional wastewatertreatment processes are not effective in treating explosive wastewater. Due to discharge toenviroment before treatment, explosive wastewater has caused various enviromental troubles,which has become a world enviromental problem and focus of the people’s concernrecently.Now the most important thing is to seek effective explosive wastewater treatmentmethods to sovle the problem.Combined ultrasound and Fenton （US-Fenton） process as anintergrated advanced oxidation technology showed vast potential for future development.Cavitation, pyrolysis, and supercritical water oxidation of ultrasound irradiation can improveFenton reaction and at the same time Fenton reaction can enhance the degradation effectiveof organic matter by ultrasound irradiation. Comparing with conventional wastewatertreatment process, US-Fenton process showed higher removal efficience in explosivewastewater treatment.On the basis of real explosive wastewater physical and chemical charactors analysis,TNTand DNAN were selected as the representive explosive pollutants and US-Fenton process wasinvolved as the treatment method. Through a series of experiments, effect factors of realexplosive wastewater, TNT wastewater, and DNAN wastewater treatments were determined.Degradation kinetics of TNT and DNAN were detected in batch and semi-batch experiments.The degradation pathways of TNTand DNAN were gotten through determingintermedia byGC-MS.Main conclusionswere drawn based on the study presented herein:（1） According to TOC removal efficience, US-Fenton process was chosen as thetreatment method. Effects of experimental conditions on real explosive wastewater, TNTwastewater, and DNAN wastewater treatment were determined and the optimal treatmentconditions were gotten. For real explosive wastewater, the optimal conditions were [TOC]0=420±20mg/L,[H₂O₂]/[Fe²⁺]=500:1, pH=2,temperature=25, US intensity=300watts/cm2, and reaction time=120minutes. Under these conditions, color, TOC, and CODremoval were86,65, and84%, respectively; for TNT wastewater, the optimal conditionswere [TNT]0=30mg/L,[H₂O₂]/[Fe²⁺]=10:1, pH=3, temperature=25, US intensity=300 watts/cm2, and reaction time=300minutes. TNT, TOC and COD removal were99.9,66.9,and81.2%, respectively; For DNANwastewaer,[DNAN]0=100mg/L,[H₂O₂]/[Fe²⁺]=100:1,pH=6, temperature=25, US intensity=300watts/cm2, and reaction time=300minuteswere the optimal conditions and DNAN, TOC, and COD removal reached100,73.8, and87.6%, respectively.（2） The degradation kinetics of TNT and DNAN were studied in batch and semi-batchexperiments. The results showed that both TNT and DNAN removals were pseudo-first-orderin batch experiment and in semi-batch experiment they were pseudo-second-order.（3） Primarily proposed degradation pathways of TNT were determined through studyingthe degradation process. The first pathway was that methyl connected to benzene wasoxidated by OH to carboxyl and TNT became TNB. Subsequently, TNB was oxidatedfutherto trinitrophenol, dinitrophenol, nitrophenol, or phenol. At last, the ultimate products ofcarbon dioxide, nitrate ions and water were given by benzene ring open, hydrolysis, andmineralization; the second one was that nitro group was reduced to amino group firstly andthen cleaved from the benzene ring. Subsequently, methyl connected to benzene was oxidatedby OH to carboxyl and phenol was given; the third one was that p-nitro group was oxidatedby OH before methyl oxidation, and then methyl became carboxyl. Subsequently, benzenering open, hydrolysis, and mineralization happened and result in identical ultimate productsas mentioned.（4） Through the study of DNAN degradation process, primarily proposed degradationpathways of DNAN were given.The first pathway was that DNAN reacted with OH togenerate2-hydroxy-4-nitroanisole,4-hydroxy-2-nitroanisole, or nitroanisole, which wereoxidated to anisole futher. Phenol as the oxidation production of anisole transformed tocarbon dioxide, nitrate ions and water through benzene ring open, hydrolysis, andmineralization; the second one was that nitro group was reduced to amino group firstly andthen cleaved from the benzene ring. Subsequently, methyl connected to benzene was oxidatedby OH to carboxyl. After that phenol was generated from benzoic acid, and then benzenering open, hydrolysis, and mineralization happened.In this study, US-Fenton process was involved to treat explosive wastewater and showedhigher removal efficiency than conventional wastewater treatment processes. Explosivematter in the wastewater can be degraded well by US-Fenton process. Therefore this studyprovide scientific basis for explosive wastewater treatment and enviroment protection.