The Fouling Behaviour Of PVDF Ultrafiltration Membrane By The Mixtures Of Dissolved Organic Matter And Typical Inorganic Foulant

To further determine the fouling mechanism of the mixtures of inorganic and organic matters. In these experiments, different sizes of silica and kaolinite were used as the inorganic foulant, humic acid（HA） and bovine serum albumin（BSA） were used as the organic foulant. Fouling experiments with HA, BSA, silica, kaolinite and organic-inorganic mixtures were carried out with PVDF ultrafiltration membranes. The interaction forces between PVDF membrane and each type of foulant and between foulant and foulant were investigated. The main conclusions are as follows:（1） When the organic foulant in wastewater is HA:（1） The flux decline rate and extent of HA-fouled ultrafiltration membrane was more seriously than that for any kind of inorganic-fouled membrane. This was mainly due to the stronger interaction forces among inorganic foulants, which resulted in the fact that the inorganic foulants aggregate into large clusters, and reduced the risk of inorganic foulants pass into membrane pores.（2） When Kaolin, micro silica and other larger size inorganic foulant and HA coexistence, the pollution behavior of organic-inorganic coexistence system changed with the concentration of inorganic foulant and the different running stages.Initial filtration, regardless of the concentration of the inorganic foulant, the presence of inorganic foulant slows down the membrane fouling. This is because the forces between the Si O₂-HA led to some HA adsorbed on the surface of inorganic foulant, reducing the adsorption accumulation of HA on the membrane surface and the probability of HA entering the membrane pores, slowing down the flux decay rate of the UF membrane.However, in the latter filtration, the cake layer formed gradually, the cake layer becamethe main factor controlling membrane fouling gradually. With the increase of the concentration of inorganic foulant in wastewater, the formation rate of cake layer is accelerated. So with the increase of the concentration of inorganic foulant in wastewater,the greater the membrane flux decay in the latter filtration.（3） The size of inorganic foulant is also the key to influence the behavior of UF membrane fouling. Compared with the membrane fouling caused by organic matter, the flux decay rate and flux attenuation amplitude of HA-nano silica are obviously increased, and with the increase of the concentration of nano silica in wastewater, the degree of membrane fouling caused by HA increased. This is because Si O₂-HA polymer formation destroyed a lot of Si O₂ together. The strong interaction between the Si O₂-PVDF makes the rapid adsorption of Si O₂ and Si O₂-HA aggregates accumulated in the membrane pores and membrane surface, which increased the membrane fouling. With the increase of the concentration of nano silica in wastewater, the content of Si O₂-HA aggregate in wastewater and the content of Si O₂ in Si O₂-HA aggregate increased, so as to increase the probability of membrane pore clogging.（2） When the organic foulant in wastewater is BSA:（1） The flux decline rate and extent of BSA-fouled ultrafiltration membrane was more seriously than that for any kind of inorganic-fouled membrane. This was mainly due to the stronger interaction forces among inorganic foulants, which resulted in the fact that the inorganic foulants aggregate into large clusters, and reduced the risk of inorganic foulants pass into membrane pores.（2） When the inorganic foulant is micro silica, in the investigated concentration range, The concentration of inorganic foulant had little effect on slowing down of BSA-fouled membrane. This is because the micro silica with BSA to form polymer is stable. And the adhesion force between BSA and PVDF is larger, so the degree of BSA-fouled membrane is more serious. The structure of the cake layer is formed rapidly, so the concentration of inorganic foulant had little effect on the rate of cake formation.（3） When the inorganic foulant is nano silica, with the increase of the concentration of nano silica in wastewater, the degree of slowing down BSA-fouled membrane also increased. This is because the greater the concentration of nano silica,the higher the degree of polymerization to form a polymer, the particle size of the formed aggregates is also larger. And with the increase of the concentration of nanosilica, the content of Si O₂ in Si O₂-BSA aggregate increased, the adsorption properties of PVDF membrane on BSA were further decreased.