Research On Removal Efficiency Of Micro-polluted Organic Matter In Pre-oxidation Process Indicated By Water Quality Parameters

Pre-oxidation technology is often used in the front-end treatment of water plants to treat micro-polluted organic matter in water source by adding chemical oxidants.Because the determination of the residual amount of micro-pollutants in water is complicated and there is no online monitoring method for the removal rate of micro-pollutants at present,it is necessary to develop one or several alternative parameters to indicate the removal efficiency of micro-pollutants in the pre-oxidation process.Respectively,this thesis explores the humic acid configuration of simulation and the actual water after being different oxidant preoxidation various water quality parameters(absorbance UV₂₅₄,for electronic ability EDC,biological can be assimilated organic carbon AOC and three-dimensional fluorescence,etc.),the change rule of parsing oxidant and natural organic matter in the process of oxidation reaction mechanism of the organic matter and slightly polluted,then reliable substitution parameters(UV₂₅₄,EDC)were established to indicate the removal efficiency of typical micro-polluted organic compounds by different oxidants in the pre-oxidation process.During the pre-oxidation of potassium permanganate（KMnO₄）,EDC decreased significantly,while UV₂₅₄ did not.The decrease of UV₂₅₄ and EDC in KMnO₄ oxidation combined with enhanced coagulation was greater than that in KMnO₄ oxidation alone.The contribution rate of KMnO₄ oxidation alone to UV₂₅₄ degradation in simulated water is 10-30%,and the contribution rate of KMnO₄ oxidation alone to UV₂₅₄ degradation in actual water is about 70%.KMnO₄ pre-oxidation process can improve the biodegradability of water body,and the AOC of actual water body increased by 3.5 times after KMnO₄ oxidation.The KMnO₄pre-oxidation process is suitable for a wide range of pH,and the removal efficiency of micro-polluted organic matter by KMnO₄ oxidation is similar under different pH conditions.In the KMnO₄ pre-oxidation process,the relative residual amount of UV₂₅₄ and EDC has a good linear correlation with the removal rate of micro-polluted organic matter,and the slope order is consistent with the second-order reaction rate constant of micro-polluted organic matter and KMnO₄.It was found that EDC was more suitable than UV₂₅₄ as a substitute parameter to indicate the removal efficiency of micropollutants in KMnO₄ pre-oxidation process.During O₃ pre-oxidation,UV₂₅₄ decreased significantly,while EDC did not.The decrease of UV₂₅₄ and EDC with t-Bu OH was greater than that without t-Bu OH.After O₃ oxidation,the 3D fluorescence of water sample was removed about 55%.O₃ pre-oxidation process can improve the biodegradability of water body,and the AOC of actual water body increases 2.5times after O₃ oxidation.pH has a certain effect on the oxidation efficiency of ozone pre-oxidation process,and O₃ has a strong ability to oxidize micro-polluted organic matter under neutral and alkaline conditions.In the O₃ pre-oxidation process,there is a good linear correlation between the relative residual amount of UV₂₅₄ and EDC and the removal rate of micro-polluted organic matter,and the order of slope is consistent with the second-order reaction rate constant of micro-polluted organic matter with O₃ and hydroxyl radical（^·OH）.After comparison,it is found that UV₂₅₄ is more suitable than EDC as a substitute parameter to indicate the removal efficiency of micro pollutants in O₃ pre-oxidation process.The activation of ferrous persulfate（Fe（Ⅱ）/PMS）is an oxidation which mainly produces free radicals,and it can simultaneously produce SO₄^·-and^·OH(mainly SO₄^·-)in the oxidation process.Mn（Ⅱ）/NTA/PMS is a kind of oxidation involving non-free radical oxidation mechanism,and the intermediate manganese contributes mainly to the oxidation.The UV₂₅₄and EDC of Fe（Ⅱ）/PMS decreased significantly during the pre-oxidation process.During the pre-oxidation of Mn（Ⅱ）/NTA/PMS,EDC decreased significantly,while UV₂₅₄ did not decrease significantly.Pre-oxidation of Fe（Ⅱ）/PMS and Mn（Ⅱ）/NTA/PMS s can increase the biodegradability of water,and the AOC of water samples increased by 1～3 times after pre-oxidation.pH has a great influence on the oxidation efficiency of the twos.Under acidic and neutral conditions,Fe（Ⅱ）/PMS and Mn（Ⅱ）/NTA/PMS have strong oxidation capacity of micro-polluted organic matter.The oxidation of Fe（Ⅱ）/PMS is non-selective,and can well oxidize other typical micro-polluted organic compounds except nitrobenzene.The oxidation of Mn（Ⅱ）/NTA/PMS has higher selectivity,and the removal effect of phenolic substances,sulfonamides and heterocyclic substances is better.There is a good linear correlation between the relative residual amount of UV₂₅₄ and EDC and the removal rate of micro-polluted organic matter in the pre-oxidation process of persulfate activated by iron and manganese.For Fe（Ⅱ）/PMS,UV₂₅₄ and EDC can be used as suitable alternative parameters to evaluate the removal efficiency of micro-polluted organic matter in the pre-oxidation process.For Mn（Ⅱ）/NTA/PMS,EDC is more suitable than UV₂₅₄ as a substitute parameter to indicate the removal efficiency of micropollutants in the pre-oxidation process.Different oxidants have certain degradation effects on UV₂₅₄ and EDC in water,but the amplitude is different.The specific performance is as follows:O₃ and Fe（Ⅱ）/PMS have the best degradation effect on UV₂₅₄,followed by Mn（Ⅱ）/NTA/PMS,and KMnO₄ oxidation has the worst removal effect on UV₂₅₄.The decrease of EDC in KMnO₄ and Mn（Ⅱ）/NTA/PMS is larger than that in Fe（Ⅱ）/PMS,and the decrease of EDC in O₃ is the smallest.The results show that during the oxidation of KMnO₄ and Mn（Ⅱ）/NTA/PMS,the electron donor part of NOM is easily destroyed,while the ultraviolet absorption part is more solid.In the oxidation process of O₃ and Fe（Ⅱ）/PMS,the ultraviolet absorption part of NOM is easily destroyed,while the electron giving part is more solid.In conclusion,these results suggest that UV₂₅₄ and EDC can be used as a substitute for different oxidants with parameter indicators in the removal efficiency of micro-polluted organic matter in the pre-oxidation process,and can better guide the application of different pre-oxidants in the oxidative degradation of micro-polluted organic matter in water treatment by means of online monitoring of alternative parameter indicators.