Enhancing <i>o</i>-cresol biodegradation in wastewater via <i>T. obliquus</i>/TiO₂ composite: construction and mechanistic insights

Microalgae are widely recognized for their eco-friendly and cost-effective contributions to water pollution mitigation. However, practical applications face efficiency and toxicity tolerance limitations. This study overcomes these hurdles by engineering a titanium dioxide-microalgae composite, <i>T. obliquus</i>/TiO₂, specifically to enhance the degradation of phenolic compounds like <i>o</i>-cresol in wastewater treatment. The results demonstrate a significant improvement, with the o-cresol degradation rate using the composite being 1.79 times higher than that of <i>T. obliquus</i> alone. This enhancement is primarily attributed to the synergistic interplay between TiO₂ nanoparticles (NPs) and microalgal metabolism, particularly photosynthesis. The TiO₂ NPs interact with chloroplasts to reduce bandgap, decrease photoelectron-hole recombination, and improve light energy utilization. Electrochemical analyses, including cyclic voltammetry (CV) and Tafel tests, reveal enhanced extracellular electron transfer, while indicators of respiratory activity and cell energy levels, such as electron transport system activity (ETSA) and adenosine triphosphate (ATP), point to increased intracellular electron transfer. Additionally, the composite shows improved biomass and metabolic activity, as indicated by total chlorophyll content and nicotinamide adenine dinucleotide (NADH) levels, alongside reduced oxidative stress markers like malondialdehyde (MDA) and superoxide dismutase (SOD). These findings offer valuable insights into sustainable strategies for organic wastewater treatment and remediation.