Photodegradation of soluble microbial products (SMPs) from membrane bioreactor by GO-COOH/TiO₂/Ag

This study aimed to explore a new degradation method - photocatalysis technology to polish membrane bioreactor (MBR) effluent, using 2,6-di-tert-butylphenol (2,6-DTBP) as a model soluble microbial product (SMP). 2,6-DTBP is one of the predominant SMPs in MBR effluent, which is refractory and difficult to biodegrade. This study developed a novel carboxylated graphene oxide/titanium dioxide/silver (GO-COOH/TiO₂/Ag) nanocomposite to photodegrade 2,6-DTBP. GO-COOH/TiO₂/Ag was successfully synthesized, using l-cysteine as the linker bonding TiO₂/Ag to GO-COOH. The structural, morphological and optical properties of the GO-COOH/TiO₂/Ag nanocomposite were characterized using various techniques. Owing to synergistic effects, the GO-COOH/TiO₂/Ag nanocomposite exhibited enhanced photocatalytic degradation performance under solar light irradiation when compared to TiO₂, Ag and GO-COOH. To remove 25 mg/L 2,6-DTBP, the reaction time for GO-COOH/TiO₂/Ag was only 30 min, faster than the 90 min required for pure TiO₂ or Ag. In addition, the 200 mg/L GO-COOH/TiO₂/Ag nanocomposite aqueous solution showed the best performance under solar light, with 99% removal of 2,6-DTBP. This enhanced capability is likely due to the surface plasmon resonance (SPR) effect contributed by Ag nanoparticles (NPs) doped onto the TiO₂. In addition, GO-COOH had a high effective surface area, which assisted in degrading the 2,6-DTBP through improved adsorption. The stability study showed that the photocatalytic activity of the GO-COOH/TiO₂/Ag was stable enough for recycling multiple times. The effective degradation performance and excellent stability demonstrates that the GO-COOH/TiO₂/Ag nanocomposite can be a promising photocatalyst in the field of effluent SMP photodegradation, which solves the problem of the difficult biodegradation of highly toxic 2,6-DTBP.