Discovery of a new volcanic soil material, "Akahoya," as an adsorbent for bacterial and viral pathogens and its application to environmental purification.

Akahoya is a volcanic soil rich in alumina, primarily deposited in Kyushu, Japan. We have found that Akahoya adsorbs bacteria in the water surrounding cattle grazing areas, suggesting a potential for environmental purification. This study investigated the spectrum of microorganisms adsorbed by Akahoya using a column filled with Akahoya through which a suspension of microorganisms was passed. Shirasu soil, another volcanic soil with a different chemical composition, was used as a control. Akahoya effectively adsorbed a diverse range of microorganisms including Escherichia coli, Campylobacter jejuni, Vibrio parahaemolyticus, Salmonella Enteritidis, Staphylococcus aureus, Clostridium perfringens, spores of Bacillus subtilis and Bacillus anthracis, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), murine norovirus, and avian influenza virus (H3N2), whereas Shirasu soil did not adsorb any of the organisms examined. Moreover, bacteria naturally present in river water, such as aerobic bacteria, total coliforms, and Enterobacteriaceae as indicators of river contamination, as well as E. coli added artificially to sterilized river water, were reduced to below the detection limit (<1 CFU/mL) after being passed through Akahoya. Additionally, the number of viable E. coli continued to decrease after contact with Akahoya for 1 month, suggesting bactericidal effects. Notably, the adsorption of E. coli to Akahoya was influenced by the concentration of phosphate and the pH of the suspension due to the interaction between the surface phosphorylation of organisms and Al2O3, the major chemical component of Akahoya. The present results demonstrate the remarkable ability of Akahoya to remove phosphate and microbes, suggesting that Akahoya could be used for water purification processes.IMPORTANCEAlthough a safe and sufficient water supply is essential for the maintenance of hygienic conditions, a major challenge is to develop a comprehensive effective, sustainable, and cost-effective technological approach for the treatment and purification of contaminated water. In this study, we demonstrated that a novel volcanic soil, Akahoya, which has unlimited availability, is a highly effective adsorbent for a wide range of bacterial and viral pathogens, suggesting its potential as a sustainable resource for this purpose. It was suggested that the adsorption of microorganisms on Akahoya was mediated by phosphate groups present on the surface structures of microorganisms, which bind to the alumina component of Akahoya according to the phosphate concentration and pH of the liquid phase. The present findings highlight the exceptional ability of Akahoya to eliminate or reduce phosphate and microorganisms effectively in water purification processes, thus contributing to the development of efficient and sustainable solutions for addressing water pollution challenges.

Fine Particle Adsorption Capacity of Volcanic Soil from Southern Kyushu, Japan.

"Akahoya" is a volcanic soil classified as a special soil deposited in Kyushu, Japan. Many of its properties are not yet clearly understood. We found that Akahoya had the potential to adsorb bacteria in cattle feces, which prompted us to investigate its material properties and perform experiments to comprehensively evaluate its adsorption performance for various fine particles such as acidic and basic dyes, NOx/SOx gas, and phosphoric acid ions, in addition to bacteria. Akahoya had a very high specific surface area owing to the large number of nanometer-sized pores in its structure; it exhibited a high adsorption capacity for both NO2 and SO2. Regarding the zeta potential of Akahoya, the point of zero charge was approximately pH 7.0. The surface potential had a significant effect on the adsorption of acidic and basic dyes. Akahoya had a very high cation exchange capacity when the sample surface was negatively charged and a high anion exchange capacity when the sample surface was positively charged. Akahoya also exhibited a relatively high adsorption capacity for phosphoric acid because of its high level of Al2O3, and the immersion liquid had a very high Al ion concentration. Finally, filtration tests were performed on Escherichia coli suspension using a column filled with Akahoya or another volcanic soil sample. The results confirmed that the Escherichia coli adhered on the Akahoya sample. The results of the Escherichia coli release test, after the filtration test, suggested that this adhesion to Akahoya could be phosphorus-mediated.

Dye Adsorption Mechanism of Glass Fiber-Reinforced Plastic/Clay Ceramics and Influencing Factors.

The effective reuse of waste glass fiber-reinforced plastic (GFRP) is desired. We previously produced porous ceramics by firing mixtures of crushed GFRP and clay in a reducing atmosphere and demonstrated their applicability as adsorbents for the removal of basic dyes from dyeing wastewater. However, the primary influencing factors and the dye adsorption mechanism have not been fully elucidated, and the adsorption of acidic and direct dyes has not been clarified. In this study, adsorption tests were conducted, and the effects of the firing atmosphere, specific surface area, type of dye, and individual components were comprehensively investigated. The results showed that reductively fired ceramics containing plastic carbide residue adsorbed basic dye very well but did not adsorb acidic dye well. The clay structure was the primary factor for the dye adsorption rather than the GFRP carbide. The mechanism for the basic dye adsorption appears to have been an increase in specific surface area due to the plastic carbide residue in the ceramic structure, which increased the ion exchange between the clay minerals and the dye. By adjusting the pH of the aqueous solution, the GFRP/clay ceramic also adsorbed considerable amounts of direct dye, so the mechanism was determined to be ion exchange with the calcium component of the glass fibers.

Porous Ceramics Adsorbents Based on Glass Fiber-Reinforced Plastics for NOx and SOx Removal.

To reuse waste glass fiber-reinforced plastics (GFRPs), porous ceramics (i.e., GFRP/clay ceramics) were produced by mixing crushed GFRP with clay followed by firing the resulting mixture under different conditions. The possibility of using ceramics fired under a reducing atmosphere as adsorbent materials to remove NOx and SOx from combustion gases of fossil fuels was investigated because of the high porosity, specific surface area, and contents of glass fibers and plastic carbides of the ceramics. NO2 and SO2 adsorption tests were conducted on several types of GFRP/clay ceramic samples, and the gas concentration reduction rates were compared to those of a clay ceramic and a volcanic pumice with high NO2 adsorption. In addition, to clarify the primary factor affecting gas adsorption, adsorption tests were conducted on the glass fibers in the GFRP and GFRP carbides. The reductively fired GFRP/clay ceramics exhibited high adsorption performance for both NO2 and SO2. The primary factor affecting the NO2 adsorption of the ceramics was the plastic carbide content in the clay structure, while that affecting the SO2 adsorption of the ceramics was the glass fiber content.

Experimental and Numerical Analyses of Temperature-Reducing-Effect by Heat of Water Evaporation on a Moss-Greening Ceramic Utilizing Waste Silica.

To recycle silica byproducts and to moderate the heat-island phenomenon, a porous ceramic was prepared by mixing waste silica powder with clay, and then firing the resultant mixture. By exploiting the high water-absorption capacity of the resulting ceramic, a greening material in which the porous ceramic was covered with moss was produced. The suppression effect of the temperature increase caused by solar-radiant heat on the moss-covered ceramic, was investigated quantitatively using the following procedure. First, the surface temperature change of the water-absorbing moss-covered sample during solar-radiant heat reception, and the amount of water that evaporated from the sample were measured simultaneously. Then, the heat of evaporation was estimated from measurements of the rate of water evaporation. Next, to investigate how much the sample temperature was reduced by heat of water evaporation, the temperature change of the sample when the heat of water evaporation was absorbed from the sample, was simulated by performing Finite Element Method (FEM) analysis. The summary of the results was as follows. (1) The primary factor of the temperature-reduction-effects on the moss-covered sample was action of heat of water evaporation. Therefore, the moss-covered sample did not exhibit much of the suppression ability of the temperature increase caused by solar-radiant heat, when the sample did not contain sufficient water. (2) This analytical method enabled us to simulate with a relatively high accuracy, the temperature change of a water-absorbing sample during solar-radiant-heat reception. Especially, the method enabled us to investigate visibly the influence of water evaporation-heat on the sample temperature, in addition to the influences of the emissivity of the sample, and the apparent specific heat and thermal conductivity changes due to water content in the sample.