Influence Mechanism Of NaClO Chlorination On Typical Organic Fouling Behavior Of Ultrafiltration Membrane

In order to explore the influence mechanism of chlorination on typical organic fouling behaviors of ultrafiltration membrane,we selected sodium hypochlorite(NaClO)for the chlorination of typical dissolved organic matters,i.e.,bovine serum albumin(BSA)and humic acid(HA),to investigate the membrane fouling behavior of polyvinylidene fluoride(PVDF)ultrafiltration membrane before and after chlorination.Atomic force microscope(AFM)was used to determine the interaction force between the foulants and membranes,and foulants themselves.Combining with the dynamic adsorption process of foulants in the membrane surface and characteristics of adsorption layer structure,the influence mechanism of membrane fouling after chlorination was investigated.And the conclusions are as followed:(1)For BSA,when the concentration of NaClO increased from 0 to 2mg/L,the membrane flux decline rate fell sharply from 89% to 15% in the 120 min running time,it was chlorination that made the force between membrane-BSA and BSA-BSA reduced,respectively from 14.56 to 7.07mN/m and from 16.2 to 2.03mN/m.In addition,it also slowed down the adsorption rate and adsorption capacity on the membrane surface,which formed a loose and porous fouling layer and then accompanied with the mitigation of membrane fouling.When the concentration of NaClO increased to 4mg/L and 6mg/L,the membrane flux decl rate gradually increased from 15% to 32% and46%,it was the continuous chlorination that led to the increase of interaction force between membrane-BSA and BSA-BSA,which increase the amount of foulants and the density of adsorption layer.Finally,the membrane fouling was aggravated.(2)For HA,when the concentration of NaClO was 0,2,4 and 6mg/L,the membrane flux decline rate was respectively 17.6%,26.4%,35.3%,and 48.4% in the120 min running time.Obviously,HA was different with BSA.The chlorination accelerated the rate and extent of HA contaminations on the PVDF ultrafiltration membrane.The main reason was when the concentration of NaClO increased from 0mg/L to 2,4 and 6mg/L,the average force between membrane and HA gradually increased from 7.93mN/m to 10.02,10.65 and 12.5mN/m,and the HA-HA also gradually increased from 0.76mN/m to 0.91,1.06 and 1.46mN/m.The increase in the force led to the increase of adsorption rate and the density of the contaminated layer.Finally,the membrane fouling was enhanced.(3)Based on the influence of chlorination on BSA and HA fouling behavior,it was found that the influence of chlorination on ultrafiltration membrane fouling was closely related to the performance of contaminations and the concentration of NaClO.For BSA,although chlorination can slow down the membrane fouling,excessive chlorination will weaken it.For HA,chlorination aggravated membrane fouling,and the force between membrane and foulants increased with NaClO dosage.Either BSA or HA,NaClO mainly changed the interaction force between membrane-foulants and foulants-foulants,and changed the adsorption and accumulation behavior of contaminations and the structure characteristics of adsorption layer,finally affected the membrane fouling behaviors.