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

Abstract

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 (10-10 particles/mL) were several orders of magnitude higher in the water than the original water solution (10 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.

Modified Local Soil (MLS) Technology for Harmful Algal Bloom Control, Sediment Remediation, and Ecological Restoration

“…Following the flocculation, a 1.5 cm thick capping was applied in the Lake Tai experiment (projects 3 and 4) using local soil. For the Cetian experiment (project 5), a 1 cm capping was applied using oxygen nanobubble-modified zeolite, which was prepared following the method described by [24]. Briefly, zeolite was placed in a pressure-resistant, airtight container to create a vacuum (−0.08 to −0.1MPa for 2 h), followed by oxygen nanobubble loading (0.12 to 0.15 MPa for 4 h), which was repeated three times to achieve super-saturation of O 2 in the zeolite micropores.…”

“…These clays can stably hold the nanobubbles for months, so that once the oxygen is delivered by settling the clay particles onto the sediment, an aerobic capping layer is formed on top of the anaerobic sediment. This oxidized capping layer can prevent the consumption of dissolved oxygen in the water column by the anaerobic substances from the sediment underneath the capping layer [24,25]. Furthermore, it has been demonstrated that emissions of the greenhouse gases CH 4 and CO 2 from eutrophic waters can be substantially reduced through the oxygen nanobubble-MLS treatment [26].…”

Lake and River Restoration: Method, Evaluation and Management

“…Phosphorus and nitrogen have long been recognised as crucial nutrients for harmful algal growth in eutrophic waters [11]. In addition to the input of external pollutants from wastewater or runoff waters, the embedded sediment-bonded nutrients can be released back to the water column, especially under hypoxic conditions at sediment-water interfaces [12]. Thus, integrated restoration strategies always consider the control of both external and internal nutrient loadings.…”

Temporal and Spatial Study of Water Quality and Trophic Evaluation of a Large Tropical Reservoir

“…The eutrophication of a river or lake has effects that can be perceived by the naked eye, such as the alteration of biota, turbid water, large amounts of aquatic plants, sediments and the development of organisms that prevent light from penetrating columns of water, which then leads to a decrease of dissolved oxygen [11][12][13].…”