Optimizing nano-sized oxygen bubble application for prolonged aerobic degradation of BTEX in contaminated groundwater.

This study investigates the use of nano-sized oxygen bubbles (NOBs) to enhance BTEX (benzene, toluene, ethylbenzene, xylene) biodegradation in groundwater. Optimized NOBs, averaging 155 nm and at a concentration of 6.59 × 10⁸ bubbles/mL, were found to provide sustained oxygen release with a half-life of approximately 50 days. Laboratory column experiments demonstrated that NOBs released up to 380% more oxygen than initially injected, significantly boosting BTEX degradation. The repeated injection of NOBs increased the volume of trapped bubbles within soil pores, enhancing long-term oxygen release efficiency by expanding the available gas phase within the porous matrix. NOB treatment resulted in markedly lower effluent BTEX concentrations and elevated gene expression linked to BTEX-degrading enzymes. This mechanism supports the sustainability of NOBs as an oxygen source, maintaining aerobic conditions over extended periods. Compared to traditional oxygen sources, NOBs improve oxygen solubility without introducing secondary pollutants, offering a novel in situ remediation strategy for urban groundwater contamination, thereby supporting long-term monitored natural attenuation (MNA).