Effect of Addition of Bacteria on the Removal of Radioactive Cesium from Ocean Sludge in a Circulation Type Purification System

Following the Fukushima nuclear accident of March 11, 2011, soil and water were contaminated by radioactive cesium. Moreover, radioactive cesium was found in the ocean sludge in Tokyo Bay, carried by rivers flowing into the bay. The cesium adsorbed in the sludge cannot easily be removed. The objective of this study was to investigate the effect of the addition of bacteria to the micro-bubble circulation system on the efficient removal of radioactive cesium from ocean sludge. One of the authors has developed an ocean sludge decomposition system employing circulation of micro-bubbles. Model sludge was prepared using seawater, sea sludge, and cesium chloride. Bacteria were added to the system after 24 h. Dried tangle extract was added as a nutrient at 24 h and 36 h. The decomposition experiment was carried out for 120 h. The circulation of micro-bubbles created an aerobic state that activated aerobic bacteria, facilitating decomposition and purification of the sludge. Thus, decomposition of the deposited sludge using our system renders the elution of the radioactive cesium possible. If the cesium is eluted in the water, we can fix it using existing technology such as zeolites. We identified and isolated the most useful bacteria for sludge decomposition. Effects on purification seem to be greatest when additional bacteria are added directly to the process. The methodology proposed is expected to facilitate decomposition of sludge and removal of radioactive cesium from the environment.