Study On The Degradation Of Typical Azo Dyes In Water By Using Electron Beam

Azo dyes are the most commonly used dye in textile and dying industry, andaccount for about60%of total output. But during the process of producing andusing, about15%of azo dyes are discharged with wastewater. Azo dye wastewater isrecognized as one of the intractable industrial wastewater and, characterized withcomplication of organic components, high colority, high quantity and change overtime and high bio-toxicity. Electron beam irradiation, as an advanced oxidationtechnology, has received more and more attention in the field of environmentalapplications in recent years. In this paper, Orange G (OG) and Procion Red MX-5B(PR MX-5B) as the typical azo dyes are taken as objects of electron beam irradiationstudy.The work mainly consists of two aspects: on the one hand, HPLC quantitativeanalysis technology was used to study the factors which affect the electron beamdegradation efficiency, such as initial concentration, irradiation dose, initial pHvalue, dosage of adding hydrogen peroxide, different experiment conditions. And thedegradation dynamics of OG solution was also studied. Degradation pathways ofOG solution was studied and speculated according to the data obtaining though theanalysis of the IC and LC-MS; On the other hand, rotifers which are most commonused in biological wastewater treatment are used as the main microbes to studyingthe bio-toxicity of OG solutions after electron beam irradiation that for furtherexploring the targets degradation mechanism.The experimental results showed that under the condition of the electron beamirradiation that:(1) the degradation of OG and PR MX-5B followed the false firstorder kinetics equation.(2) Under certain irradiation dose, the degradation rate ofthe targets reduced with the initial concentration of the solution increased. Forexample, under2kGy, when the initial concentration of OG solution increased from50mg/L to500mg/L, and the degradation rate decreased from69.8%to7.2%; In the same situation, the degradation rate of PR MX-5B solution decreased from69.8%to7.2%, while its initial concentration increased from100mg/L to500mg/L.(3) Found that the degradation rate of the targets raised with the irradiation doseincreased, when studied the influence of irradiation dose at a fixed initialconcentration. For example,200mg/L OG solution, when the radiation doseincreased from0.5kGy to10kGy, the degradation rate rose from10.8%to58.76%.And PR MX-5B solution also follows this rule.(4) When the other reactionconditions remains constant, the degradation rate in acidic and alkalineenvironments of the two azo dyes were higher than in neutral conditions, and thedegradation rate in acid condition was a little higher than in alkaline environment.The pH value of both azo dye solutions gradually decreased during irradiation.(5)The addition of hydrogen peroxide increased the quantity of hydroxyl radicals whichare good for the remove of the dye molecules. However, the excess hydrogenperoxide could inhibit the degradation of the dye molecules.(6) The degradation rateof OG solution in three radiolysis system follow the order: OH oxidative systemwith oxygen> eaq-reductive system> oxidative-reductive system, while PR MX-5Bsolution followed another order: OH oxidative system with oxygen>oxidative-reductive system> eaq-reductive system.(7) According to the analysis ofIC, HCOO-, CH3COO-, NO3-and NO2-were found during the degradation process ofOG solution.(8) The degradation mechanism of OG in oxidative environment was,OH attack azo bond firstly, OG molecules were cleaved into naphthalenecompound, and then OH could further degraded it into dicarboxylic acid.Finally, it was found that at moderate doses (about5kGy), system producedsome poisonous by-products which resulted in stronger inhibition rate to rotifersthrough monitoring toxic change of the OG solutions due to incomplete degradation.The higher concentration, the greater of bio-toxicity OG solutions is. Meanwhile, thetoxicity of solutions reduced with the radiation dose increased.Electron beam irradiation technology can effectively degrade azo dye wastewater. However, in the dealing process, the selection of irradiation andquantity of oxidant should according to the actual situation as not to inhibit thedegradation efficiency and avoid producing toxic byproducts, to optimize theprocessing.