Danxi Huang

Fouling behavior of typical organic foulants in polyvinylidene fluoride ultrafiltration membranes: characterization from microforces.

To further unravel the organic fouling behavior of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes, the adhesion forces of membrane-foulant and foulant-foulant were investigated by atomic force microscopy (AFM) in conjunction with self-made PVDF colloidal probe and foulant-coated colloidal probe, respectively. Fouling experiments with bovine serum albumin, sodium alginate, humic acid, and secondary wastewater effluent organic matter (EfOM) were carried out with PVDF UF membrane. Results showed a positive correlation between the membrane-foulant adhesion force and the flux decline rate and extent in the initial filtration stage, whereas the foulant-foulant interaction force was closely related to the pseudostable flux and the cake layer structure in the later filtration stage. For each type of foulant used, the membrane-foulant adhesion force was much stronger than the foulant-foulant interaction force, and membrane flux decline mainly occurred in the earlier filtration stage indicating that elimination of the membrane-foulant interaction force is important for the control of membrane fouling. Upon considering the foulant-foulant interaction force and the membrane flux recovery rate of fouled membranes, it was evident that the main contributor to physically irreversible fouling is the foulant-foulant interaction force.

Identifying polyvinylidene fluoride ultrafiltration membrane fouling behavior of different effluent organic matter fractions using colloidal probes

The interaction forces between effluent organic matter (EfOM) fractions and membrane were measured by atomic force microscopy in conjunction with self-made membrane material colloidal probes. The inter-EfOM-fraction and intra-EfOM-fraction interactions were investigated using corresponding EfOM-fraction-coated colloidal probe. We combined this analysis with corresponding fouling experiments to identify the EfOM fractions responsible for polyvinylidene fluoride (PVDF) ultrafiltration membrane fouling. Results show that hydrophilic and hydrophobic fractions were the dominant fractions responsible for membrane fouling and flux decline in the initial and later filtration stages, respectively, which was mainly attributed to the stronger PVDF-hydrophilic fraction and intra-hydrophobic-fraction interaction forces. This phenomenon, in conjunction with the fact that each interaction force of PVDF-EfOM fraction was stronger than corresponding intra-EfOM-fraction force, suggests that the elimination of the PVDF-hydrophilic fraction interaction force is the best strategy for controlling EfOM fouling. Moreover, the inter-EfOM-fraction interaction force was mainly controlled by the corresponding intra-EfOM-fraction interaction forces. And, while the membrane-EfOM fraction and intra-EfOM-fraction interactions for each type of EfOM fraction are equivalent, the EfOM fractions with the molecular weight smaller than the molecular weight cutoff of the membranes used were mainly responsible for membrane fouling rather than the relatively high-molecular-weight fractions.

Effect of protein on PVDF ultrafiltration membrane fouling behavior under different pH conditions: interface adhesion force and XDLVO theory analysis

To further determine the fouling behavior of bovine serum albumin (BSA) on different hydrophilic PVDF ultrafiltration (UF) membranes over a range of pH values, self-made atomic force microscopy (AFM) colloidal probes were used to detect the adhesion forces of membrane–BSA and BSA–BSA, respectively. Results showed that the membrane–BSA adhesion interaction was stronger than the BSA–BSA adhesion interaction, and the adhesion force between BSA–BSA-fouled PVDF/PVA membranes was similar to that between BSA–BSA-fouled PVDF/PVP membranes, which indicated that the fouling was mainly caused by the adhesion interaction between membrane and BSA. At the same pH condition, the PVDF/PVA membrane–BSA adhesion force was smaller than that of PVDF/ PVP membrane–BSA, which illustrated that the more hydrophilic the membrane was, the better antifouling ability it had. The extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory predicts that the polar or Lewis acid–base (AB) interaction played a dominant role in the interfacial free energy of membrane–BSA and BSA–BSA that can be affected by pH. For the same membrane, the pH values of a BSA solution can have a significant impact on the process of membrane fouling by changing the AB component of free energy.

Preparation of PVDF hollow fiber ultrafiltration membrane via phase inversion/chemical treatment method

AbstractPoly(vinylidene fluoride) (PVDF) hollow fiber membranes were prepared via a phase inversion/chemical treatment method, using N,N-dimethylacetamide (DMAc) as solvent, Calcium carbonate as inorganic additive, and water and HCl as coagulation media. Effects of external coagulation bath and bore fluid composition on membrane performance were investigated by using scanning electron microscopy, mechanical properties, porosity, average bubble point pressure, and permeation performance. The results show that: (1) The cross-section morphology of membranes have no significant change, exhibiting a two-layer finger-like structure extended to the middle of the cross-section. (2) The roughness of the external surface increased considerably and the number of the surface pores increased as well when we introduced HCl as the second coagulation. The permeation experiments reveal that acid treatment had no impact on fibers which had precipitated completely. (3) The number and pore size underlying the inner skin laye...

Fouling behavior of urban sewage on binary blend PVDF UF membrane

AbstractPolyvinylidene fluoride (PVDF) ultrafiltration membranes with better performance were prepared by blending with PVA, polyvinylpyrrolidone, polyethylene glycol, and polymethylmethacrylate through phase inversion via immersion precipitation method. Phase inversion progress of membranes was investigated though light transmittance experiment. Membrane components and morphologies were analyzed by FTIR, scanning electron microscopy, and atomic force microscopy, respectively. Membrane performance was evaluated in terms of pure water permeation, BSA rejection, and water contact angle. Membranes fouling behavior was evaluated according to dynamic fouling resistance analysis, using secondary effluent of urban sewage as separation object. The results showed that PVDF UF membranes with high hydrophilicity, dense surface, and through macrovoids in cross-section had small sewage flux decline and low fouling during filtration, and the main fouling resistance was due to concentration polarization and cake layer r...

Effect of electrokinetic property of charged polyether sulfone membrane on bovine serum albumin fouling behavior

Negatively charged carboxymethylated polyethersulfone (CMPES) and positively charged quaternized polyethersulfone (QAPES) ultrafiltration (UF) membranes were prepared by bulk chemical modification and non-solvent induced phase separation method. The effects of PES membrane interfacial electrokinetic property on the bovine serum albumin (BSA) membrane fouling behavior were studied with the aid of the membrane-modified colloidal atomic force microscopy (AFM) probe. Electrokinetic test results indicated that the streaming potential (ΔE) of QAPES membrane was not consistent with its expected IEC value, however, within the pH range of 3–10, the ζ potentials of two charged-modified PES membranes were more stable than the unmodified membrane. When pH value was 3, 4.7 or 9, the interaction behavior between charged PES membrane and BSA showed that there was significant linear correlation between the jump distance r0 of membrane-BSA adhesion force (F/R) and the ζ potential absolute value. Charged modification significantly reduced the adhesion of PES membrane-BSA, and the adhesion data was good linear correlated with the flux decline rate in BSA filtration process, especially reflected in the CMPES membrane. The above experimental facts proved that the charged membrane interfacial electric double layer structure and its electrokinetic property had strong ties with the protein membrane fouling behavior.

Study of antifouling modified ultrafiltration membrane based on the secondary treated water of urban sewage.

Mixtures of polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) containing hydrophilic ultrafiltration membranes were prepared by adding PVA (5 to 30%) to PVDF by the phase inversion method. The hydrophilic contact angle (CA), equilibrium water content, pure water flux and bovine serum albumin retention were studied to assess the membrane performance. The anti-fouling performance of modified membrane to the secondary treated water was evaluated by flux decline, washing recovery rate and fouling resistance analysis. Scanning electron microscopy showed that the cross-section structure of the membranes had finger-like pores, which were well developed and uniformly distributed, and the sub-layer structure was looser and more porous with the increasing content of PVA. The CA gradually decreased. The steady flux was 800 L/m(2) h from P15 to P30, and the BSA retention sharply declined. The ultrafiltration tests for secondary treated water indicated that the main fouling source of the modified membrane was the concentration polarization and cake layer resistance. After physical flushing, the flux recovery ratio of the membrane could reach 100% when the PVA content was 5-15%, which shows excellent anti-pollution performance and good prospects for use in processing wastewater from urban sewage.

Dye effluent treatment using PVDF UF membranes with different properties

AbstractUsing DMAc as solvent, water as non-solvent, modified poly(vinylidene fluoride) (PVDF) ultrafiltration membranes (PSi, PA, PS) were prepared by precipitation phase inversion, blending with nano-silica (SiO2), polyvinyl alcohol (PVA), and styrene maleic anhydride. The physical-chemical properties and morphology of PVDF membranes were characterized by FT-IR, water contact angle (WCA), swelling index, scanning electron microscopy, atomic force microscopy, etc. Considering reactive black 5 and congo red as the representatives of dye effluent pollutions, the filtration behavior to dye wastewater of four different types of PVDF UF membranes was discussed. Experimental results showed that, compared with original PVDF UF membrane, for three kinds of modified membrane, the first bubble pressure and strength (S) fell off to a certain extent, and the membrane surface roughness increased. Additionally, the cross-sectional macroporous and pure water flux (J) all increased. Especially, owing to the addition of ...

New insight into the adsorption behaviour of effluent organic matter on organic–inorganic ultrafiltration membranes: a combined QCM-D and AFM study

Adsorption of organic matter on membranes plays a major role in determining the fouling behaviour of membranes. This study investigated effluent organic matter (EfOM) adsorption behaviour onto poly(vinylidene fluoride) (PVDF) membrane blended with SiO2 nanoparticles using quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). The QCM-D results suggested that low adsorption of EfOM and an EfOM layer with a non-rigid and open structure was formed on SiO2-terminated membrane surfaces. Conformational assessment showed that EfOM undergoes adsorption via two steps: (i) in the initial stage, a rapid adsorption of EfOM accumulated onto the membrane; (ii) the change in dissipation was still occurring when the adsorption frequency reached balance, and the layer tended towards a more rearranged or organized secondary structure upon adsorption onto the more hydrophilic surface. For the AFM force test, when a self-made EfOM-coated probe approached the membrane, a ‘jump-in’ was observed for the hydrophobic membrane after repulsion at a small distance, while only repulsive forces were observed for PVDF/SiO2 membranes. This study demonstrated that the PVDF/SiO2 membrane changed the entire filtration process, forming a ‘soft’ open conformation in the foulant layer.

The effect of PVDF concentration on PVDF/woven tube composite membranes and the application of composite membranes in SMBR

AbstractUsing fiber woven tube for support layer, the poly vinylidene fluoride (PVDF)/woven tube composite hollow fiber membrane with high strength and high water flux was prepared through the coating technology and immersion-precipitation technique. The effect of PVDF contents on membrane flux and porosity was investigated; using the homemade composite membrane in the sequencing batch membrane reactor (SMBR) reactor. The rejection effect on particles and the changes of the composite membrane performance were also studied. With the increase of PVDF concentration, pure water flux and the average pore diameter of the composite membrane decreased, but the burst pressure increased; the porosity increased at first and then decreased. In this research, porosity of composite membrane is always above 45%, the burst pressure is higher than 0.30 MPa, and the tensile strength of the composite membrane is very high. Although the membrane is operated at a high flux (20 ± 0.5 L m−2 h−1) in the SMBR system, the transmem...