[Adsorption Mechanisms Analysis of EfOM on PVDF Ultrafiltration Membranes Modified by SiO2 Using QCM-D and AFM].

To further unravel adsorption mechanisms of effluent organic matter (EfOM) on the PVDF ultrafiltration membranes modified by nano-silica particles from micro perspective during different filtration phases, the membranes were prepared by adjusting the dosage of nano-silicon. The adsorption of EfOM on the surface of the membranes and the interaction between EfOM and the membranes were measured by quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM).The QCM-D results suggested that adsorbing capacity and adsorption rate of EfOM on the hydrophilic surfaces were lower than on the hydrophobic surfaces. Meanwhile, it was found that EfOM underwent adsorption via two steps: In the initial 15 min stage, a rapid adsorption of EfOM accumulated onto the membrane surface; The change in dissipation still occurred when the EfOM adsorption frequency reached balance, which demonstrated that the adsorption of EfOM remained unchanged on the membrane surfaces, and changes in the conformation of adsorption layer still occurred. For the AFM force test, it was found that the EfOM-membranes and EfOM-EfOM interactions declined with the increase of hydrophily, which revealed the essential reason for the decrease of adsorbing capacity and adsorption rate. The combined utilization of QCM-D and AFM effectively explained the effect of modified membranes on adsorption mechanisms of EfOM.

[Adhesion Force Analysis of Protein Fouling of PVDF Ultrafiltration Membrane Using Atomic Force Microscope].

To determine the fouling behavior of bovine serum albumin (BSA) on differet hydropniic PVDF ultrafiltration membrane over a range of pH, atomic force microscopy (AFM) and self-made colloidal probes were used to detect the microscopic adhesion forces of membrane-BSA and BSA-BSA, respectively. The results showed a positive correlation between the flux decline extent and the membrane-foulant adhesion force in the initial filtration stage, whereas the foulant-foulant interaction force was closely related to the membrane fouling in the later filtration stage. Moreover, the membrane-BSA adhesion interaction was stronger than the BSA-BSA adhesion interaction, which indicated that the fouling was mainly caused by the adhesion interaction between membrane and foulant. At the same pH, the adhesion force between PA membrane-BSA was smaller than that of PP membrane-BSA, illustrating the more hydrophilic the membrane was, the better the antifouling ability it had. The adhesion force between BSA-BSA fouled PA membrane was similar to that between BSA-BSA fouled PP membrane. These results confirmed that elimination of the membrane-BSA adhesion force is important to control the protein fouling of membranes.

[Efficacy of A2/O-MBR Combined Process in Wastewater Treatment and the Characteristics of Membrane Fouling].

The hydrophilic modification of PVA composite membrane was applied in the reversed A2/O-MBR process to treat wastewater, the removal efficacy of COD, NH4(+) -N, TN, TP, turbidity and performance of composite membrane were investigated. The results indicate that the average removal rates of COD, NH4(+) -N and TP were higher than 90%, 95% and 80% under different reflux ratio, respectively. The reflux ratio had large impact on TN removal rate: when the reflux ratio was 100%, the removal rate was low; when the reflux ratio increases the range from 100% to 300%, the removal rate was correspondingly increased. Under the efficient interception of membrane, water turbidity was always less than 0.05NTU, and the composite film was controlled at (12 ± 0.5) L x (m2 x h)(-1) flux, the operation was uninterrupted for 52 days without any cleaning process of the membrane, the average rate of membrane fouling is 13.22 Pa x h(-1) and the process of membrane fouling was very slow. After FTIR analysis, we confirmed that polysaccharide and protein is a main composition of organic pollutants. LB is further proved to be the main pollutants from micro acting force between the membrane and the pollutants, which is consistent with FTIR analysis.

[Experimental study of adhesion properties between membrane surface and humic acid during microfiltration].

To further unravel the humic acid (HA) fouling mechanism during microfiltration under different conditions, such as pH, ionic strength, the concentration of calcium ions, atomic force microscopy (AFM) combined with self-made PVDF colloidal probe was applied to determine the relationship between the adhesion forces of membrane-HA or HA-HA and the flux decline of membrane. The results indicate adhesion forces were the main reason of membrane fouling. With the decrease of pH or increase of the ionic strength, due to the electrical neutralization caused by pH and electrical shielding effect of ionic strength, the adhesion forces of membrane-HA and HA-HA increased. Because of the comprehensive effect of "salt bridge" and electrical neutralization, there was a transition from increase to decrease for the adhesion forces of membrane-HA and HA-HA as the doses of calcium ions increased. In all cases, both of membrane-HA and HA-HA adhesion forces had the same variation tendency, which displayed a good correlation with the flux decline trends during fouling experiments, respectively, and provided certain theoretical support to further understand the formation mechanism of membrane fouling.

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.