| The ultrafiltration process has become the core of the third generation of water treatment technology,and has achieved large-scale application,but membrane fouling has become a key constraint factor for its stable and efficient operation.Inline flocculation and coagulationflocculation can replace traditional flocculation sedimentation process to achieve reduction of drug consumption and sludge production through membrane pollution control.However,there is a lack of in-depth and systematic quantitative research on the relationship between the membrane pollution control effect of these two simplified processes and the dosing mode,type and amount of chemicals.At the same time,their control effect on effluent quality deserves attention.In this study,the water transferred from the south to the north into Beijing is taken as raw water,and the control effect of inline flocculation and coagulation-flocculation on ultrafiltration membrane pollution with or without high voltage static electric field coupling is systematically investigated,and the influence of coagulant types and concentrations on membrane foouling and organic matter removal is explored,providing technical and theoretical support for the stable operation of water plant with ultrafiltration process.Spectral analysis is used to study the removal effect of different treatment processes on the precursors of disinfection by-products and other organic substances,so as to provide guidance on the technical optimization of flocculation ultrafiltration operation to control disinfection by-products for water plants.According to this study,the main results are as follows:(1)The control of PAC coagulant at the same dosage on ultrafiltration membrane fouling is better than that FeCl3 coagulaant during inling flocculation process.Reversible membrane fouling is the main fouling,and PAC has better mitigation effect on reverisble membrane fouling and irreversible membrane fouling than FeCl3.In the coagulation flocculation process,within the range of 1.5～4.5mg/L Me3+,the control effect of the two on ultrafiltration membrane pollution is similar,and PAC can better slow down irreversible membrane pollution.According to Hermia model analysis,complete plugging,standard plugging,critical plugging and cake layer plugging all contribute to membrane fouling in online flocculation ultrafiltration and coagulation flocculation ultrafiltration processes,and cake layer plugging is the main reason for membrane fouling in online flocculation ultrafiltration and coagulation flocculation ultrafiltration processes.(2)The combination of high voltage electrostatic field and flocculation pretreatment on the online flocculation ultrafiltration process reduces the membrane pollution resistance in varying degrees,and the membrane pollution reduction effect is better under the condition of low coagulant dosage concentration than under the condition of high coagulant dosage.Based on the analysis of Hermia membrane pollution model,it can be seen that the membrane pollution process in the online flocculation high voltage electrostatic field ultrafiltration process at low concentration is still dominated by filter cake layer plugging filtration,which is the combined effect of high voltage electrostatic field changing floc size,increasing floc branching and enhancing Zeta potential.However,after the high-voltage electrostatic field is coupled to the coagulation flocculation process,the membrane pollution of the subsequent ultrafiltration process is aggravated,and both reversible and irreversible pollution are aggravated.The analysis of membrane fouling mechanism shows that the fouling caused by complete plugging and standard plugging mode is the key factor.(3)In the online flocculation ultrafiltration and coagulation flocculation ultrafiltration process sections,the removal of organic matters is mainly in the flocculation process section,and the removal efficiency of total organic matters in the former is lower than that in the latter.Under the same effective concentration,the removal rate of DOC by PAC coagulant is higher than that of FeC13,but the removal effect of the two coagulants on the types of organics in raw water is different:in the online flocculation process,FeC13 has better removal effect on hydrophobic substances,while the removal rate of humic acid organics and tryptophan organics by PAC is higher than FeC13;The removal rate of soluble microbial products by coagulation flocculation process is higher than that of tryptophan protein.DCAcAm is the most common disinfection by-product of organic matter in the effluent of online flocculation,while TCAcAm is the most common disinfection by-product in the coagulation flocculation mode.The coupling of high voltage electrostatic field has no significant effect on the effluent quality.(4)Correlation analysis was conducted by using floc characteristics(Zeta potential,fractal dimension,median particle size)and membrane fouling resistance under different reagent conditions in different periods.The results showed that the median particle size during online flocculation was significantly negatively correlated with membrane fouling resistance.Under the action of electrostatic field in coagulation flocculation technology,the median particle size of floc was negatively correlated with membrane fouling resistance.The water quality was analyzed by threedimensional fluorescence spectrum and ultraviolet spectrum,and the correlation between PARAFAC,FRI,characteristic spectrum UV254,A254/A204 and the content of disinfection byproduct precursor was established.The results showed that under different flocculation modes,PAC,as a coagulant,had a significantly better correlation between the removal of relevant organic matter and the formation of carbon containing disinfection by-products than FeC13.On line flocculation mode FRI data can indicate and predict the generation potential of some carbon containing disinfection by-products;In the process of coagulation flocculation,the three-dimensional fluorescence spectrum analysis results of PARAFAC and the monitoring of UV254 are more suitable for quantitative prediction of nitrogen containing disinfection by-products. |
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