Study On The Degradation Of Chlorophenols And Bromophenols In Water By Using Electron Beam

Chlorophenols （CPs） and bromophenols （BPs） are the main two kinds ofhalophenols （HPs）. CPs and BPs are widely used in pesticides, flame retardants, dyes,polymers, intermediates and other industrial production. Besides that, BPs in themarine can also be formed through natural process. Because of containing halogenatoms on the benzene ring structure of HPs, which have high toxicity, refractory andbiological accumulation, so the potential environmental risk harm can not be ignored.In this paper, six different kinds of systems were taken as objects of study: singleortho-chlorophenol （2-CP）, single ortho-bromophenol （2-BP） aqueous solution andtheir mixed solution, single para-chlorophenol （4-CP）, single para-bromophenol（4-BP） aqueous solution and their mixed solution, these target materials wereirradiated by electron beam.The work mainly involves two aspects: on the one hand, HPLC quantitativeanalysis technology was used to study degradation dynamics of single ortho-andpara-position chlorophenols or bromophenols aqueous solution and their own mixture.The various influence factors （such as initial concentration, irradiation dose, initial pHand H₂O₂solution, etc.） on its irradiation degradation process were also researched.Degradation pathways of mixture were studied and speculated according to the dataobtaining through the analysis of the IC and LC-MS; on the other hand, the luminousbacteria experiments were performed to monitor toxic changes during the degradationof these different kinds of systems for further exploring the targets degradationmechanism.The experimental results showed that under the condition of the electron beamirradiation, the degradation of target followed false first order kinetics equation.Under the condition of the same initial concentration, the target objects degradationrate increased with the increase of irradiation dose; under the same irradiation dose,the degradation rate were decreased with increasing initial concentration. Compared with the single material solution, the degradation rates of mixture were lower, forexample, when at the dose of4kGy, initial concentration was75mg/L, thedegradation rate of separate4-CP and4-BP both are about97%, however, thedegradation rates of4-CP and4-BP in the mixed system were81%and91.5%,respectively. The degradation rate is relatively high of the para-position bycomparison to the ortho-postion halogenated phenol separate degradation. pH canaffect the yield of active particles produced through the water radiolysis, the researchshows that the removal rates have a higher level in the acidic conditions than in theneutral or alkali conditions. The introduction of H₂O₂can increase the quality of OHradical that plays a main role during electron beam degradation, the concentration ofH₂O₂in the experimental range is advantageous to the removal of the target. Inaddition to the Cl-ions in the para-position mixed system, the releasing Br-and Cl-ions concentration basically increased with the dose in the process of electron beamirradiation. Furthermore, formic acid, acetic acid were not detected, but only a smallamount of oxalic acid was generated. The products of the hybrid system under lowdosage were analyzed by LC-MS, it was speculated that the main degradationintermediate in the two mixed system may both are muconic acid. Besides, other toxicby-products may be generated through oxidation and structural rearrangement,halogenated benzoquinone may be produced during the process of ortho mixturedegradation, para mixed degradation process can produce3-chloro phthalates quinoneand bromo-p-benzoquinone.Finally, it was founded that at low irradiation dose （≈1kGy）, due to incompletedegradation, system can produce some poisonous by-products which resulted instronger inhibition rate to light-emitting bacteria through monitoring toxic change ofthe target systems. The toxicity of chlorophenols were higher than that ofbromophenols. Meanwhile hybrid systems have higher toxicity than their singlesolution which suggests that hybrid system will produce synergy. The para singlehalogenated phenol toxicity were stronger than the ortho position. Toxicity of each target system decreased with the increase of irradiation dose.Electron beam can effectively degrade monomers and hybrid systems of ortho-and para-position chlorophenols or bromophenols. But in the process of irradiation,the irradiation dose should be controlled appropriately to avoid producing toxicby-products at lower doses, to optimize the processing.