Attribution of photocatalysis of fluorescent natural organic matter fractions to the alleviation of ceramic membrane ultrafiltration fouling

In this study, a novel composite functioned as adsorption-photocatalysis based on bismuth oxide (Bi2O3), reduced graphene oxide and titanium dioxide (TiO2) (labelled as BRGT) was applied in combination with ceramic membrane ultrafiltration to removal natural organic matter (NOM) and to mitigate membrane fouling. The mechanisms of NOM removal and of membrane fouling were investigated. The dual action of adsorption and photocatalysis by the BRGT effectively degraded NOM, giving a removal efficiency of 22.2 % for dissolved organic carbon and 73.0 % for UV absorbance at 254 nm. ·O2− radicals were mainly involved in the degradation of humic and protein/polyphenol-containing fluorescent components of NOM. BGRT had a high adsorption affinity for protein-like components, whose removal depended more on h+. The fouling behavior of the ceramic membrane was the result of pore blocking combined with cake filtration formation. BRGT mainly adsorbed hydrophobic components, which exacerbated the reversible fouling resistance and transformed the fouling mechanism from standard blocking into complete blocking. With increase of photocatalytic time, the hydrophobic fraction was converted into hydrophilic and transphilic fractions, and large and medium molecular weight organics were degraded into small molecules. In this case, the cake filtration formation occurred much earlier, with reversible membrane resistance reduced by 95.5 % and irreversible membrane resistance reduced by 90.4 % at 60 min. From the results we concluded that NOM can be effectively treated with adsorption-photocatalysis by BRGT, especially its fluorescent fractions, which has great potential in alleviating ceramic ultrafiltration membrane fouling.