Influence Of Ionic Strength And Different Electrical Protein On Ultrafiltration Membrane Fouling Mechanism

Ultrafiltration technology was widely used in sewage treatment and reuse.However,in the process of actual operation,it was the main barriers to restrict the high efficient of low consumption in operation that membrane fouling caused by soluble organic matter in waste water.And a large amount of protein organic matter was a kind of typical membrane pollution in wastewater.Thus,it was very important to prove protein organic pollution mechanism of membrane fouling control.This article selected the bovine serum albumin(BSA)on behalf of protein in the water pollutants.Respectively in the BSA positively charged,negatively charged and neutral condition,the examined the interaction force feature between ultrafiltration membrane-BSA and BSA-BSA along with the change of ionic strengths,and combined with the corresponding conditions BSA adsorption behavior and the characteristics of adsorption layer structure on the PVDF ultrafiltration membrane,and macroscopic ultrafiltration membrane filtration test,membrane flux recovery and characteristics of BSA removal rate,and analysed different electric protein ultrafiltration membrane fouling under different ionic strengths.The main results were as follows:(1)On the basis of our previous research,the succeeded preparation BSA colloidal probe of micron grade,and verified the practicability of the preparation BSA colloid probe.By atomic force microscopy(AFM)combined with BSA colloid probe,implemented measure the interaction force between PVDF ultrafiltration membrane-BSA and BSA-BSA under the various water quality conditions,and provided technical support for resolving the micro mechanism of protein pollution with ionic strengths.(2)The first examined PVDF ultrafiltration membrane pollution behavior of BSA under the pH 3.0,namely BSA with positively charged.The results found that BSA membrane fouling rate and the pollution extent increased gradually when the ionic strength increased from 0 to 100 mmol/L,mainly because of the change of the electrostatic force that was the dominant factor controlling the BSA pollution behavior.Electrostatic attraction between PVDF-BSA led to BSA quick covering the membrane surface,thus the BSA interaction force became the dominant factor to control membrane fouling.And electrostatic repulsion between BSA-BSA decreased,with the increase of ionic strength,led to BSA adsorption cumulative rate increased and the BSA pollution layer was more and more denseon on the membrane surface,and the rates of membrane fouling gradually increased.Completely followed the DLVO theory.(3)Under the pH 4.7,namely BSA isoelectric point,the membrane fouling rate and the pollution rate increased with the increase of ionic strength when the ionic strength increased from 0 to 1 mmol/L;But when the ionic strength increased from 1 to 100 mmol/L,membrane fouling rate and the pollution rate decreased with the increase of ionic strength.This was largely because,under the condition of low ionic strength,electrostatic force was the main factor controlling membrane fouling.However,when the ionic strength continued to increase,the BSA and membrane surface accumulated a lot of hydrated cation,and effectively triggered the hydration repulsion between PVDF-BSA and BSA-BSA.Not only reduced the BSA adsorption accumulated on the membrane surface,also formed loose and porous BSA pollution layer on the membrane surface,resulting in membrane fouling slowing down.(4)Under the pH 9.0,BSA negatively charged conditions,membrane fouling rate increased with the increase of ionic strength caused by BSA when the ionic strength increases from 0 to 10 mmol/L;But when the ionic strength was 100 mmmol/L,the corresponding rate of membrane pollution and pollution range began to decrease significantly.This was similar with the conditon of BSA isoelectric point,mainly because the change of the electrostatic force was the main factor controlling membrane fouling under the condition of low ionic strength.But when ionic strength reached a certain value,the emergence of hydration repulsion became the main factor affecting the membrane fouling.However,compared with the isoelectric point BSA,negatively charged BSA seems to be less likely to trigger hydration reaction force.