Biological removal and recovery of selenium

Biological removal and recovery of selenium (Se) from selenium-laden wastewater holds promise as it could potentially provide a stable, circular Se supply and eliminate the toxic effects of Se contamination. On the one hand, the recovery of Se from the Se-laden wastewater could provide an alternative Se source, potentially uncoupling the Se supply from the production of its parent material and alleviating the high Se demand in the application. On the other hand, Se recovery is of importance to improve the applications on biological treatment processes, which are challenged by the production of amorphous elemental selenium (BioSe0), suspended in the treated water or attached to the biomass. Further effluent/solid waste treatment is needed for the bioprocesses; otherwise, they would bring potential risks for re-releasing and mobilizing toxic Se in the environment. Compared to the amorphous BioSe0, hexagonal crystalline BioSe0 is more favorable for recovery due to its larger density, detachment from the biomass, and potentially crystal growth to form a bigger size. Therefore, this thesis studied the production of highly pure recoverable elemental selenium (i.e., crystalline BioSe0) with a relatively high selenate reduction rate for potentially removing and recovering Se from Se-laden wastewater. Two pathways were proposed to achieve the promising selenium bio-recovery: (1) the recrystallization of amorphous Se0 to crystalline Se0; (2) the production of crystalline Se0 from SeS2 via a combination of selenate to selenite process and the sulfate-reducing process