For various pollutants with different specific gravity values, adsorbents having similar specific gravity values as those of target pollutants are necessary to achieve enough contact time. The purpose of this work is to introduce a self-vertical migration system to adsorbents for wastewater treatment. An alginate hydrogel composite with controlled specific gravity and buoyancy was successfully developed, which can first sink to the bottom of water and then float up on the surface after the adsorption. The alginate hydrogel composite was prepared using an alginate solution containing both glucose and yeast. In an experiment, the obtained beads first sank. However, 30 min later, most of them floated up to the water surface, where carbon dioxide was generated in the fermentation process. This behavior was repeated several times during the fermentation process, causing the beads to float. To confirm the efficiency of this unique property, the removal of cesium ions was demonstrated in a water column using Prussian Blue modified alginate gel beads with a repeated vertical migration system. The adsorbent showed a faster removal of cesium than the other adsorbents without the proposed system. We believe that the proposed system can be applied to treat large volumes of wastewater that cannot be stirred or pumped. Therefore, the novel adsorbent developed in this study is expected to significantly contribute to environmental remediation.
Keywords: adsorbent; buoyancy-control; eco-material; vertical migration; water purification.