Key Techniques In The Hybrid Process Of Enhanced Coagulation By Complex Pre-oxidation And Ultrafiltration In Drinking Water Treatment

Nowadays,drinking water sources in northern China have been seriously polluted by organic matters,posing a big challenge for the upgrade of conventional drinking water treatment processes.A novel process combining coagulation-ultrafiltration and new complex pre-oxidation techniques has been proposed in this study in order to achieve effective water treatment from those sources contaminated by organic matters.First of all,the effects of KMnO₄,O₃ and their combination on the coagulation by PAC were investigated.Results showed that the combination of KMnO₄ and O₃ could significantly improve the removals of turbidity and organic matters.Particularly,the sequence of KMnO₄ and O₃ dosages was of great importance.Humic-like natural organic matters could be effectively removed due to the synergetic effect of KMnO₄and O₃ when they were both dosed simultaneously.In the condition of O₃ 2mg/L,KMnO₄ 0.5mg/L and PAC 30mg/L,the removals of turbidity and TOC in the process of pre-oxidation were 60%and 26%,respectively.SUVA value of the effluent was1.88.The water quality after treatment met the national standard for drinking water.After that,the effects of KMnO₄,O₃ and their combination on the physical and chemical characteristics of dissolved natural organic matters were investigated,basing on their hydrophilicity/hydrophobicity and molecular weight.It was concluded that ozonation targeting at hydrophobic organic matters with large molecular weight could change these organic matters into smaller but more hydrophilic ones.The oxidation capability of KMnO₄ was much weaker than that of O₃,by which organic matter removal was mainly because of the adsorption by MnO₂ particulates decomposed from KMnO₄,therefore,leading to poor removal selectivity.The effluent composition after treatment by both KMnO₄ and O₃ was almost the same as that after treatment by O₃.However,thanks to the catalysis of MnO₂,more weak hydrophobic acidic organic matters were able to be removed via pre-oxidation of both KMnO₄ and O₃.In addition,according to the effluent quality and membrane fouling in both coagulationsedimentation-ultrafiltrationprocessandintegrated coagulation-ultrafiltration process,the dosing position and dosage of KMnO₄ were optimized.When 0.5mg/l KMnO₄ was spiked into the membrane tank,TOC in the membrane filtrate decreased to 4%,and membrane fouling rate decreased by 19%.MnO₂ particulates decomposed from KMnO₄ could adsorb organic matters and therefore decrease the organic matter load of membrane.Moreover,with the sedimentation of MnO₂ particulates on membrane surface,the fouling layer became loose and its hydrophilicity increased,which benefited membrane fouling reduction as well.In both coagulation sedimentation-ultrafiltration process,the proposed two-position dosing mode?equal amount before and after coagulation?was much more effective in terms of membrane fouling alleviation and fouling irreversibility reduction.Last but not least,a novel drinking water treatment process based on two-time KMnO₄dosagesinthehybridprocessofozonation-coagulation sedimentation-ultrafiltration was proposed.The dosage of KMnO₄ with O₃ in the pre-oxidation tank could enhance humic-like natural organic matter removal by coagulation while the dosage of KMnO₄ in the membrane tank could decline the formation and development of membrane fouling.When 0.75mg/L KMnO₄?two portions were used in the pre-oxidation tank,and one portion was used in the membrane tank?,2mg/L O₃,30mg/L PAC were adopted,the removal of TOC were60%,while the membrane fouling rate was increased by only 15%.The overall effluent quality met the standard for drinking water.This two-time KMnO₄ dosage process is simple and flexible,and can be used for the update of conventional drinking water treatment plant in order to achieve effective treatment of micro-polluted water.