TiO₂ nanoparticles accelerate methanogenesis in mangrove wetlands sediment

In this study, the response of methane (CH₄) production to the addition of titanium dioxide nanoparticles (TiO₂ NPs) with three types of short-chain fatty acids (sodium acetate, sodium propionate and sodium butyrate) as carbon sources in mangrove sediment was investigated. The results showed that the maximum CH₄ formation rate increased by 45.2%, 32.7% and 48.6% and the maximum cumulative CH₄ production increased by 25.2%, 7.7% and 6.3% with the addition of TiO₂ NPs in the sodium acetate, sodium propionate and sodium butyrate systems, respectively. The microbial community analysis revealed that the electrogenic bacteria Proteiniclasticum and Pseudomonas, butyrate oxidizing bacteria Syntrophomonas and methanogens Methanobacterium and Methanosarcina were significantly enriched in the presence of TiO₂ NPs, indicating that TiO₂ NPs can enhance CH₄ production by stimulating the growth of different species of methanogens and butyrate oxidizing bacteria. The enlarged distance between microbes, the enhanced conductivity of the sediment and the typical microorganisms for direct interspecies electron transfer (DIET) with the addition of TiO₂ NPs suggest that the promoted DIET between distinct microorganisms could be another possible explanation for the improvement in CH₄ production. It can be speculated that a weaker effect on methanogenesis increases under the natural concentration of TiO₂ NPs compared with the experimental conditions; however, the amounts of TiO₂ NPs are increasing enriched in wetland environments. Therefore, the findings of this study increase current knowledge about the effect of nanomaterials on global CH₄ emissions and suggest that the discharge of wastewater containing TiO₂ NPs from the synthesis and incorporation of TiO₂ NPs in customer products needs to be monitored.