Hypoxia Remediation and Methane Emission Manipulation Using Surface Oxygen Nanobubbles

Abstract

Algal blooms in eutrophic waters often induce anoxia/hypoxia and enhance methane (CH₄) emissions to the atmosphere, which may contribute to global warming. At present, there are very few strategies available to combat this problem. In this study, surface oxygen nanobubbles were tested as a novel approach for anoxia/hypoxia remediation and CH₄ emission control. Incubation column experiments were conducted using sediment and water samples taken from Lake Taihu, China. The results indicated that algae-induced anoxia/hypoxia could be reduced or reversed after oxygen nanobubbles were loaded onto zeolite micropores and delivered to anoxic sediment. Cumulated CH₄ emissions were also reduced by a factor of 3.2 compared to the control. This was mainly attributed to the manipulation of microbial processes using the surface oxygen nanobubbles, which potentially served as oxygen suppliers. The created oxygen-enriched environment simultaneously decreased methanogen but increased methanotroph abundances, making a greater fraction of organic carbon recycled as carbon dioxide (CO₂) instead of CH₄. The CH₄/CO₂ emission ratio decreased to 3.4 × 10^-3 in the presence of oxygen nanobubbles, compared to 11 × 10^-3 in the control, and therefore the global warming potential was reduced. This study proposes a possible strategy for anoxia/hypoxia remediation and CH₄ emission control in algal bloom waters, which may benefit global warming mitigation.