Satoshi Anzai’s research while affiliated with Yokohama Rubber Co. Ltd. and other places

Demands for “green” additives that control the crystal growth and inhibit the scale formation in industrial processes are growing as never before. Nanobubbles can be the green additive for inhibiting and/or promoting the crystal growth of calcium carbonate, given their well-known unique physicochemical properties. This paper reports for the first time the changes in the crystal growth rate of calcite in liquid in the presence of air nanobubbles. We injected the air nanobubbles into the solution and studied the calcite crystal growth for the first 4 hours in a static condition at 20°C and 88°C. We found that air nanobubbles retarded the growth rate of calcite crystal by up to 53% and 33% at 20°C and 88°C, respectively. The retardation of calcite crystal growth could differ with different number densities of air nanobubbles added to the solution. A higher number density of nanobubbles generally showed slightly greater retardation throughout the tested 4 hours. Air nanobubbles may influence the crystal growth either by changing solid-liquid interfacial tension on the crystal surface, reducing the free growth sites, adsorbing Ca²⁺ ions, playing roles in bubble mattress and thermal buffering on the crystal surface, or combinations of them. Our findings suggest that air nanobubbles can be utilized as a green inhibitor of calcite crystal growth and calcium carbonate scale in broad industrial areas.

Hydrogen sulfide (H2S) is a toxic gas, and considerable research has been conducted for its control and removal from industrial wastewater and sewage water. However, no simple and practical technology is available for degrading H2S in situ at tunnel constructing sites. On May 11, 2020, an H2S blowout accident occurred in underground soil at a residential sewer-tunnel construction site in Iwakuni City, Yamaguchi Prefecture, Japan, filling the tunnel with high concentrations of H2S gas, causing the fatality of one worker owing to emphysema. River water flowing near the site was immediately introduced into the tunnel to trap the H2S gas, generating 652-m³ water that contained high concentrations (120 mg/L) of dissolved H2S in the tunnel. To safely and quickly remove H2S in situ, the contaminated water was treated with high-density oxygen and ozone nanobubbles (O2/O3-HDNBs) generated using the ultrafine pore method. Consequently, H2S was removed from the contaminated water in 3 days. This is the first successful application of O2/O3-HDNB technology for the in situ oxidation of H2S in environmental water at a construction site. This study reports the practical application of this advanced technology and the system performance.

Metallic corrosion is a major issue that leads to an efficiency loss and eventual failure of the system in geothermal power plants. Despite the growing understanding of mechanisms of corrosion, inhibiting steel corrosion in the acidic geothermal fluids remains to present formidable challenges due to its intrinsic physicochemical complexity. Here, we study the use of nanobubbles as a possible corrosion inhibitor by testing alteration(?) of the low-carbon steel plates immersed in acidic geothermal water with continuously injected air-nanobubbles. Nanobubbles have been used in a broad range of areas as they are eco-friendly, low-cost, easy-to-use and high-functional materials. We, for the first time to our knowledge, found that air-nanobubbles could inhibit steel corrosion, with inhibition efficiency of up to 50% in the studied acidic geothermal fluid. Air-nanobubbles could act as a nanoscopic coating material in the acidic geothermal fluid, through generating a bubble mattress and/or promoting nucleation and aggregation of a very small quantity of amorphous silica precipitation on the surface of steel plates. Our finding suggests that nanobubbles can inhibit steel corrosion in various chemically different geothermal fluids, highlighting the physicochemical significance of nanobubbles as the coating material for inhibiting metal degradation in the geothermal infrastructures.

Maie, N., Anzai, S., Kakino, W., Tarauya, H., 2020. Removal of 1,4-dioxane in groundwater using ozone nanobubbles. Journal of medical & hygienic use of ozone 27(4), 140-145. Abstract Removing 1,4-dioxane from environmental water using conventional advanced oxidation process (AOP) technology is costly. The need therefore exists to establish economical and simple wastewater treatment technologies. Here, we verified the effectiveness of ozone-nanobubbles (O3-NBs) in the removal of 1,4-dioxane from actual contaminated groundwater at a laboratory scale. We removed 1,4-Dioxane from actual contaminated groundwater with a half-life of 45–80 min by introducing O3-NBs at a rate of 0.53 mmol/L/h. The use of O3-NBs may therefore be practical for removing 1,4-dioxane from environmental water to realize target levels under appropriate conditions.