Development of simplified biofilm sorption and diffusion experiment method using Bacillus sp. isolated from Horonobe Und
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Development of simplified biofilm sorption and diffusion experiment method using Bacillus sp. isolated from Horonobe Underground Research Laboratory. Kotaro Ise, Tomofumi Sato, Yoshito Sasaki and Hideki Yoshikawa Radionuclide Migration Research Group, Geological Isolation, Research and Development Directorate, Japan Atomic Energy Agency (JAEA), 4-33 Muramatsu Tokai-Mura, Naka-gun, Ibaraki 319-1194, Japan ABSTRACT We developed a simplified biofilm sorption and diffusion experiment method. The biofilms of the Bacillus cereus were incubated on cellulose acetate membrane filters (pore size 0.2 μm, diameter 47 mm) placed on thick NB broth agar medium (thickness was about 30 mm) to support sufficient biofilm growth of the Bacillus cereus. The thickness of the formed biofilms was about 1 mm. The formed biofilms were applied to through-diffusion method, which has been used to measure diffusion coefficient of crystalline and sedimentary rocks and clay minerals. The obtained copper sorption coefficient by batch experiments was about 100 ml/g (wet weight) at the case of the concentration of cupper ion was over 0.074mmol/L. And diffusion coefficients by through diffusion experiment was De=1.1 x 10-10 (m2/s). From these results, this simplified biofilm sorption and diffusion experiment may make possible to obtain these parameters with ease. INTRODUCTION Recently, many studies have been conducted to develop a sorption model of radionuclides to predict transport phenomena after geological disposal [1]. Most of these studies treat only sedimentary rocks, crystalline rocks and clay minerals like bentonite [2]. However, in reality it is thought that these solid surfaces are covered with natural organic matter and most of these organic matters are biofilms [3]. It is thought that these affect aqueous phase concentration and sorption capacity of rocks [4]. Anderson et al. reported that Gallionella ferruginea biofilms concentrate trace metals up to 1000 fold higher than found within the host rock [5]. From these results, it is thought that the existence of biofilms obviously affects transport of radionuclides. Bacterial cell walls contain acid functional group and if these are deprotonated, that adsorb much cations. Therefore, the existence of bacteria affects groundwater chemistry [6]. A lot of studies about bacterial adsorption have been done, but there are quite few studies about biofilm adsorption. From these results, there are no consensus whether biofilm retard or stimulate radionuclide transport. To solve these problems, we should quantify sorption capacity and diffusion coefficient to predict the effect of biofilm covering. So far, there are almost no quantitative data about sorption capacity for radionuclides. This may due to the difficulties of sample preparation; biofilms are too fragile to treat quantitative analysis. In this study, we conducted sorption and diffusion experiment to establish simplified biofilm sorption experiment using Bacillus cereus related bacteria which were isolated from the Horonobe Underground Researc
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