Study On The Removal Of Disinfection By-Products Precursors In Drinking Water By Ultraviolet/Peroxymonosulfate

In the process of chlorination disinfection in water plants,organic matter in source water will undergo a series of reactions to generate a large number of disinfection by-products（DBPs）.Most DBPs have carcinogenic,teratogenic,mutagenic and other toxic effects,which threaten human health.Therefore,it is necessary to explore efficient removal techniques of DBPs precursors to control the production of DBPs.Firstly,haloacetonitrile（HANs）and halonitromethane（HNMs）detection methods were established.Secondly,the influence of a series of parameters in UV/PMS advanced oxidation technology on the removal characteristics of disinfection by-product precursors and the formation characteristics of carbon disinfection by-products（C-DBPs）,nitrogen disinfection by-products（N-DBPs）and adsorbable organic halogen（AOX）in the subsequent chlorination process were explored.The main research contents and conclusions are as follows:An automatic liquid-liquid extraction-gas chromatography-mass spectrometry method was developed for simultaneous detection of 6 HANs and 6 HNMs in water.10 mL water samples were extracted under the conditions of pH=2,adding 1 g anhydrous sodium sulfate,1 mL methyl tert-butyl ether,stirring speed of 600 rpm and stirring time of 5 min.After extraction,the extraction was determined by gas chromatogram-mass spectrometry.The results showed that the 12 target disinfection byproducts had a good linear relationship in a certain concentration range,and the correlation coefficients were all greater than 0.999.The lower limit of the method was 0.10～0.30μg/L,the detection limit was 0.02～0.10μg/L,and the recoveries were 73.2%～117.8%.The precision is 0.1%～8.9%.The method relied on a fully automatic pre-multifunctional automatic sample pretreatment platform to realize the whole process of automatic sample measurement,which is suitable for the high-throughput detection of HANs and HNMs in drinking water.In this study,humic acid（HA）,a typical precursor of disinfection by-products,was selected for research.Through the comparison of five oxidation technologies,H₂O₂,PMS,UV,UV/H₂O₂ and UV/PMS,UV/PMS technology was found to be better.In UV/PMS system,with the increase of PMS concentration and the extension of UV time,the removal rate of TOC,UV₂₅₄,and SUVA₂₅₄ of HA increased,and the organic matter of HA containing conjugated double bonds and aromatic structure decreased.In the process of UV/PMS degradation of HA,hydroxyl radicals（HO^·）and sulfate radical(SO₄^·-)to large molecules such as humic acid substances into building blocks and low molecular-weight acids,and then completely mineralization.For the influence of DBP and AOX formation,DBP and total AOX formation along with the increase in the PMS dose and UV time presents a trend of reducing the rise,this was mainly because less HO^·and SO₄^·-,macromolecular hydrophobic humic acid into small molecule organic matter,which result in the formation of DBPs.Compared to neutral,acidic and alkaline conditions,UV/PMS had better HA removal and lower DBP and AOX formation.Effect of water quality components on the degradation of HA by UV/PMS and the formation of DBPs after chlorination.Within a certain concentration range,the degradation of HA by UV/PMS was inhibited by nitric acid,nitrous acid and bicarbonate,and the formation of DBPs and AOX increased after chlorination.The degradation of HA was inhibited first and then promoted by increasing ammonia nitrogen and bromide ions.DBP and AOX formation increased first and then decreased with the increase of ammonia nitrogen concentration after chlorination.Nitrogen nitrate and nitrogen nitrite significantly increased the formation of dichloronitromethane（DCNM）and TCNM.The presence of ammonia nitrogen significantly increases the generation of DCAN.Bicarbonate can promote C-DBP formation,but has no significant effect on N-DBP formation.When bromide ions were present,Br-DBPs,which were dominated by TBM and DBAA,were generated after UV/PMS preoxidation,and chlorinated DBPs were continuously converted to brominated DBPs after chlorination.In conclusion,The UV/PMS technology affects DBP formation in the subsequent chlorination process by changing the organic matter concentration,fluorescent substances and molecular weight distribution of DBP precursors.In addition,the effects of water components on the degradation of DBP precursors and the formation of DBP intermediates during UV/PMS oxidation could promote or inhibit the generation of DBP after chlorination.