| The process of purifying and removing colloidal particles almost covers the whole water treatment process.Filtration is an extremely important part of drinking water treatment,and it is responsible for water quality control.Therefore,the study of the transport behavior and deposition mechanism of colloidal particles in the filtration process has very important theoretical and practical significance.In this paper,polystyrene microspheres were used to simulate colloidal pollutants,in order to study the migration behavior and deposition mechanism of colloidal particles in filter media.The main contents and conclusions of this research are as follows:Firstly,the transport behavior and deposition mechanism of the colloid in the column were systematically investigated from the three aspects of colloid characteristics（model colloid and Microcystis aeruginosa）,media characteristics（media roughness）and solution characteristics（tetracycline）.Studies showed that 1)There were obvious contrast in the transport behavior of ideal colloids（polystyrene microspheres）and Microcystis aeruginosa in the column.Regardless of the ionic strength,media size,flow rate,and the presence or absence of dissolved organic matter in the water,Microcystis aeruginosa could pass through the column.Pre-oxidation and filtration were hardly helpful for the removal of Microcystis aeruginosa.DLVO theory cannot explain the transport behaviors of the algae well.2)The study of media surface roughness on colloidal particles transport behavior systematically proved that the media surface roughness affected the colloid deposition in a non-linear and non-monotonic way,and had nothing to do with the energy barrier.There was the critical roughness related to the theoretical minimum DLVO interaction.However,the critical roughness was not necessarily the same as the roughness at the minimum deposition rate of the colloidal particles.The change in DLVO interaction energy related to ionic strength could’t fully explain the experimentally measured particle deposition differences related to the surface roughness of the column.3)It was found that TC had a weak inhibitory effect on the migration of MPs in K+solution（C/C0 decreased by 0-5.9%compared with that without TC）.In the presence of TC in Ca2+solution,the difference between the maximum and minimum adhesion efficiency of MPs was 60.99%,while it was 193.15%in the absence of TC.The presence of TC increased the mobility of MPS and maked the deposition rate of MPs less sensitive to the change of ionic strength.In KCl solution,the presence of TC（MPs）had no significant effect on the attachment efficiency of MPs（TC）,but with the increase of ionic strength,the attachment efficiency of MPs and TC changed non-linearly and non-monotonously.In general,the cotransport behavior of MPs and TC in the column was more complicated than their individual transport behavior.Secondly,a multi-scale experimental method of column transport-microfluidic device-colloidal probe was established in order to verify the deposition mechanism in the column transport experiment.The influence of ionic strength（IS）and flow rate on the transport of MPs were studied.IS and flow rate had a synergistic effect on the deposition of MPs,especially under the unfavorable conditions of low flow rate.In the column transport experiment,the difference in deposition rate between the maximum deposition condition and the minimum deposition condition became smaller as the flow rate decreased.However,in the microfluidic experiment,the difference between the deposition rate under high and low IS conditions was not sensitive to the change of flow rates.With the help of atomic-force colloid probe technology,the force distance curves of colloid filter interface under different ionic strength were measured directly from the perspective of interaction force,and the interaction potential energy was calculated.It was found that the interaction potential energy calculated by Zeta potential based on DLVO theory was nearly one order of magnitude higher than that calculated by interface force.Finally,the individual transport behavior and the cotransport behavior of MPs in the presence of humic acid（HA）were compared.The results showed that different concentration of HA enhanced the transport of MPs in a non-linear and non-monotonic form.A new model of the cotransport of saturated solutes based on the competitive deposition of MPs and HA in a filter column was established by introducing the competitive blocking viewpoint into the simulation of the cotransport of colloid in a filter column.According to the modeling results,a small amount of competitive blocking occurred during the cotransport. |
