Combating hypoxia/anoxia at sediment-water interfaces: A preliminary study of oxygen nanobubble modified clay materials.

Combating hypoxia/anoxia is an increasingly common need for restoring natural waters suffering from eutrophication. Oxygen nanobubble modified natural particles were investigated for mitigating hypoxia/anoxia at the sediment-water interface (SWI) in a simulated column experiment. By adding oxygen nanobubble modified zeolites (ONMZ) and local soils (ONMS), the oxygen nanobubble concentrations (105-107 particles/mL) were several orders of magnitude higher in the water than the original water solution (104 particles/mL) within 24 h. In the column experiment, an oxygen-locking surface sediment layer was formed after capping with ONMZ and ONMS particles. The synergy of diffusion of oxygen nanobubbles and retention of oxygen in this layer contributes to both the increase of DO and reversal of hypoxic conditions. The overlying water had significantly higher dissolved oxygen (DO) values (4-7.5 mg/L) over the experimental period of 127 days in ONMZ and ONMS compared with the control systems (around 1 mg/L). Moreover, the oxidation-reduction potential (ORP) was reversed from -200 mV to 180-210 mV and maintained positive values for 89 days in ONMZ systems. In the control systems, ORP was consistently negative and decreased from -200 mV to -350 mV. The total phosphorus (TP) flux from sediment to water across the SWI was negative in the ONMZ and ONMS treated systems, but positive in the control system, indicating the sediment could be switched from TP source to sink. The oxygen-locking capping layer was crucial in preventing oxygen consumption caused by the reduced substances released from the anoxic sediment. The study outlines a potentially promising technology for mitigating sediment anoxia and controlling nutrient release from sediments, which could contribute significantly to addressing eutrophication and ecological restoration.