Selenium (Se) is a rare metal refined from the by-product produced from copper anode slimes. Japan is the largest producer of Se in the world. Each year approximately 40 tons of Se is discarded in wastewater. As, in many regions, wastewater contains a low concentration of Se, which is masked by the high levels of other metal contaminants, it is challenging to recover pure Se using the currently available treatment technologies. Therefore, it is important to develop novel technologies to recover and recycle Se from wastewater, especially in Japan, as it is poor in metal resources. To recover Se from wastewater using bio-hydrometallurgy, we isolated Pseudomonas stutzeri NT-I, which reduces soluble seleno-oxyanions to insoluble elemental selenium (biomineralization) and produces volatile dimethyl diselenide (DMDSe) (biovolatilization) from elemental selenium. We investigated the effects of several factors significant for the reduction of seleno-oxyanions and the DMDSe synthesis rate, such as temperature, pH, agitation speed, and aeration rate, using a 5-L jar fermenter, and developed two methods for Se recovery from wastewater by controlling biovolatilization and biomineralization using P. stutzeri NT-I. The rates of selenium recovery from wastewater by biovolatilization and biomineralization were 35.9% at 120 h, and 78.8% at 24 h, respectively. Furthermore, elemental selenium was refined with a purity of 99%, or higher, either by an oxidation-reduction reaction, or by oxidizing roasting from each recovered compound. Thus, our study demonstrates that P. sutzeri NT-I can be used for the recovery of rare metals from wastewater.
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