Membrane fouling due to the presence of natural organic matter (NOM) in water and wastewater significantly compromises membrane performance and increases energy footprint in filtration, and frequent membrane cleaning with intensive chemical use is required to mitigate fouling in industrial practice. A novel photocatalytic membrane system, with integrated photocatalysts (e.g., titanium dioxide (TiO<sub>2</sub>)) producing a series of reactive oxygen species (ROS) under light irradiation, hold promise for mitigating NOM fouling because of NOM oxidation and degradation under ROS attack. To understand the mechanism of fouling control in the photocatalytic membrane system, fouling behavior of a probe NOM, humic acid (HA), and its photocatalytically oxidized product, oxidized humic acid (o-HA), on polyvinylidene fluoride (PVDF) ultrafiltration membranes have been investigated and discussed. Physical properties (i.e., wettability, structure, morphology) of HA and o-HA fouled membranes were characterized by contact angle analysis, scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively<b>.</b> HA and o-HA were characterized by Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) to determine functional groups and bond environment in the foulants. AFM was also used to analyze mechanical properties of a foulant layer (i.e., cohesiveness), and most importantly, the adhesive force of foulant-foulant and foulant-PVDF membrane. The preliminary results showed that HA fouled membranes had a higher root mean squared (RMS) surface roughness than o-HA fouled membranes (56.3-213.7 nm vs. 47.9-73.1 nm), and HA fouled membrane more significantly in reducing water flux than o-HA (24.1% vs. 5.0% flux reduction in 1.7 h filtration, with the same foulant concentration of 10 mg/L as COD). These results suggest that photocatalytic oxidation of HA may increase foulant hydrophilicity and mitigate membrane fouling. Our research will unravel the fouling mechanism of NOM in photocatalytic membrane system, and will provide insights in the design and application of novel photocatalytic membranes with improved performance for water purification.

Evaluation of photocatalytic membrane fouling by humic acid

253rd National Meeting (2017)

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