Fouling mechanisms of Pseudomonas putida on PES microfiltration membranes

Tanning Wastewater Treatment by Ultrafiltration: Process Efficiency and Fouling Behavior

Ultrafiltration is a promising, environment-friendly alternative to the current physicochemical-based tannery wastewater treatment. In this work, ultrafiltration was employed to treat the tanning wastewater as an upstream process of the Zero Liquid Discharge (ZLD) system in the leather industry. The filtration efficiency and fouling behaviors were analyzed to assess the impact of membrane material and operating conditions (shear rate on the membrane surface and transmembrane pressure). The models of resistance-in-series, fouling propensity, and pore blocking were used to provide a comprehensive analysis of such a process. The results show that the process efficiency is strongly dependent on the operating conditions, while the membranes of either PES or PVDF showed similar filtration performance and fouling behavior. Reversible resistance was the main obstacle for such process. Cake formation was the main pore blocking mechanism during such process, which was independent on the operating conditions and membrane materials. The increase in shear rate significantly increased the steady-state permeation flux, thus, the filtration efficiency was improved, which resulted from both the reduction in reversible resistance and the slow-down of fouling layer accumulate rate. This is the first time that the fouling behaviors of tanning wastewater ultrafiltration were comprehensively evaluated, thus providing crucial guidance for further scientific investigation and industrial application.

Optimization of preoxidation to reduce scaling during cleaning-in-place of membrane treatment

This study investigated the potential for reducing scaling during chemical cleaning of polyvinylidene fluoride membranes by optimizing preoxidation dose and pH. Membranes were fouled by a solution containing inorganic foulants (aluminum, iron, and manganese), humic acid, and kaolin at a Ca⁺² strength of 0.5 mM and varying the preoxidation dose. Energy-dispersive spectroscopy was used to verify the presence of inorganic foulants after cleaning. Fourier-transform infrared spectroscopy revealed changes in CCl and C-F functional groups, with bond vibrations at 542 cm^-1 and 1199 cm^-1, respectively. Minimum irreversible fouling of 5.4% and maximum flux recovery of 88.8% of the initial value were associated with a preoxidation dose of 1.5 mg/L and pH 8.5. A decrease in amount of aluminum from 5.79 ± 0.021 mg to 3.85 ± 0.054 mg in the presence of humic acid with a removal efficiency greater than 60% was due to alteration of the feed solution, as revealed by mass-balance analysis. Membrane characterization and fouling reversibility analysis confirmed that preoxidation of the feed solution produced less scaling during chemical cleaning. The cake layer fouling contribution was determined by fitting results of Hermia's fouling model analysis, with 1.34-1.85 times lower total fouling indices and 3-5.5 times lower chemically irreversible fouling indices at pH 8.5 and a preoxidation dose of 1.5 mg/L.

Identification of fouling mechanisms in MBRs at constant flowrate: model applications and SEM-EDX characterizations

A fundamental understanding of fouling mechanisms is critical to improving filtration operations. The performance of four parallel membrane bioreactors (MBRs) with different sludge retention times (SRTs) was monitored during long-term constant flowrate filtration. The characteristics of the membrane and transmembrane pressure (TMP) profiles obtained were studied to demonstrate fouling mechanisms. Both classical blocking models and their combined models were evaluated. The intermediate model provided very good agreement with all the TMP data. However, the combined cake-intermediate and intermediate-standard models were more effective in the description of the experimental data. Contributions analysis indicated that the cake, intermediate and standard blocking models were the dominant fouling mechanisms. Scanning electron microscopy and energy dispersive X-ray (SEM-EDX) imaging showed that cake blocking by organic matter and standard blocking by inorganic matter made the main contributions to membrane fouling. The combined cake-intermediate and intermediate-standard models may be applicable to systems where these two models are consistent with the experimentally observed fouling mechanisms in an MBR.

Surface Functionalization of Polyethersulfone Membrane with Quaternary Ammonium Salts for Contact-Active Antibacterial and Anti-Biofouling Properties

Biofilm is a significant cause for membrane fouling. Antibacterial-coated surfaces can inhibit biofilm formation by killing bacteria. In this study, polyethersulfone (PES) microfiltration membrane was photografted by four antibiotic quaternary ammonium compounds (QACs) separately, which were synthesized from dimethylaminoethyl methacrylate (DMAEMA) by quaternization with butyl bromide (BB), octyl bromide (OB), dodecyl bromide (DB), or hexadecyl bromide (HB). XPS, ATR-FTIR, and SEM were used to confirm the surfaces’ composition and morphology. After modification, the pores on PES-g-DMAEMA-BB and PES-g-DMAEMA-OB were blocked, while PES-g-DMAEMA-DB and PES-g-DMAEMA-HB were retained. We supposed that DMAEMA-BB and DMAEMA-OB aggregated on the membrane surface due to the activities of intermolecular or intramolecular hydrogen bonds. Bacteria testing found the antibacterial activities of the membranes increased with the length of the substituted alkyl chain. Correspondingly, little bacteria were observed on PES-g-DMAEMA-DB and PES-g-DMAEMA-HB by SEM. The antifouling properties were investigated by filtration of a solution of Escherichia coli. Compared with the initial membrane, PES-g-DMAEMA-DB and PES-g-DMAEMA-HB showed excellent anti-biofouling performance with higher relative flux recovery (RFR) of 88.3% and 92.7%, respectively. Thus, surface functionalization of the PES membrane with QACs can prevent bacteria adhesion and improve the anti-biofouling activity by the contact-active antibacterial property.

Microfiltration process for surface water treatment: irreversible fouling identification and chemical cleaning

Irreversible fouling before (left) and after (right) chemical cleaning.

Preparation of a novel PSf membrane containing rGO/PTh and its physical properties and membrane performance

Recent advances in the fabrication of nanostructures such as graphene-related materials have received a lot of attention in membrane technology for the future of water supplies.