Membranes

Despite the robust mechanical and chemical stability that make hollow flat-sheet ceramic membranes highly attractive for membrane bioreactors (MBRs), the fundamental relationship between their structural design, specifically pore size and structural symmetry, and biological fouling behavior remains elusive. To decouple the effects of membrane architecture on fouling mechanisms, a series of symmetric and asymmetric hollow flat-sheet alumina membranes were systematically engineered. Symmetric architectures with tunable pore sizes were fabricated by controlling aggregate particle sizes, whereas asymmetric counterparts featuring distinct separation layer thicknesses were developed via a tailored dip-coating process. Long-term operational evaluations treating municipal wastewater uncovered a counterintuitive phenomenon. Asymmetric membranes, despite yielding superior retention, experienced markedly accelerated transmembrane pressure evolution and severe cake layer fouling compared to the symmetric supports. Resistance-in-series analysis coupled with classical filtration models demonstrated that thicker separation layers and larger pore sizes were associated with shifts in the dominant fouling mechanism toward rapid and dense cake layer formation, which significantly exacerbated irreversible biological fouling. Furthermore, advanced spectroscopic and high-throughput sequencing techniques revealed that structurally complex asymmetric layers were associated with shifts in extracellular polymeric substances and specific fouling-associated bacterial phyla at the membrane interface. Ultimately, these findings underscore the necessity of architectural optimization to mitigate biofouling and prolong the operational lifespan of ceramic membranes, highlighting the sustainable advantages of symmetric structures.

Efficient interfacial water dissociation is essential for reducing the operating voltage of bipolar membranes (BPMs), whereas aggregation and nonuniform distribution of nanoscale catalysts can limit active-site utilization. In this study, polydopamine-modified halloysite nanotubes (PDA@HNTs) were used as a support for β-FeOOH loading to construct a composite catalytic interlayer for BPMs. XRD, FTIR, XPS, SEM, TEM, EDS mapping, contact-angle measurements, electrochemical tests, and bipolar membrane electrodialysis were used to evaluate the interlayer structure and membrane performance. At 50 mA cm⁻², the β-FeOOH-PDA@HNTs-BPM exhibited a transmembrane voltage of 0.94 V, compared with 2.15 V for the blank BPM, while the interfacial water-dissociation resistance decreased from 3.873 to 0.980 Ω. After 48 h of continuous operation, the voltage increased only from 0.94 to 0.98 V. In electrodialysis, the membrane achieved a current efficiency of 81.4% and an energy consumption of 3.3 kWh kg⁻¹ after 180 min. PDA-functionalized HNTs promote the dispersion and interfacial association of β-FeOOH, improve interfacial wettability and catalytic-site accessibility, and thereby enhance water dissociation and acid/base production in BPMs.

Membrane distillation, a separation technology, has drawn wide attention in industries such as seawater desalination and high-salinity wastewater treatment. However, conventional steady-flow operation suffers from flux decline and membrane fouling, while standard square-wave and sine-wave pulsations provide limited enhancement and stability. To address these issues, this study introduces heartbeat-mimicking pulsatile flow. Its effects on membrane distillation performance were evaluated through comparative (steady vs. pulsatile) experiments, a three-level orthogonal experiment, and tests with various feed solutions and modified membranes. Results show that, under baseline conditions, the heartbeat-mimicking pulsatile flow yielded a 17.5% higher average flux than steady flow, while its conductivity increase was only 25%, far below the 93% for steady flow. In the orthogonal experiment, the heartbeat-mimicking waveform accounted for the largest proportion of total variance (50.1%) among the tested parameters. Furthermore, compared to traditional sine or square waves, this biomimetic pulsation features unique acceleration-rest characteristics, making it highly applicable to complex feed solutions and effectively mitigating membrane fouling. This study aims to identify a new pulsation mode that can overcome the limitations of steady-flow membrane distillation.