Removal of selenite from wastewater in a Phanerochaete chrysosporium pellet based fungal bioreactor

The performance of a novel fungal bioreactor system containing pellets of Phanerochaete chrysosporium was investigated in a continuously operated bioreactor for 41 days to remove selenite (SeO32−) from synthetic wastewater. These fungal pellets were produced in situ under batch conditions during 4 days of incubation in the presence of SeO32− (10 mg Se L−1, 5 g glucose L−1, pH-4.5). Subsequently, the system was continuously fed with SeO32− at selenium and glucose loading rates of 10 mg Se L−1d−1 and 0.95 g glucose L−1 d−1, respectively, and a hydraulic retention time of 24 h. After achieving steady-state removal profiles (8 days, ∼70% removal from 10 mg Se L−1d−1), the biomass was partially removed, once every 4 days, in order to limit the excessive growth of the fungus. Afterwards, the fungal pelletized reactor was tested for its response to an increase in the SeO32− loading rate from 10 to 20 mg Se L−1d−1. During this phase (8 days), although there was a declining trend in the removal of SeO32−, the bioreactor showed good resilience to the doubled SeO32− concentration. The bioreactor was further subjected to intermittent spikes of SeO32− (30-50 mg Se L−1) once every 4 days. The bioreactor showed a good adaptability and flexibility by recovering to every intermittent spike of SeO32−, achieving ∼70% total soluble Se removal from the continuous Se loading rate (10 mg Se L−1d−1). The presence of SeO32− influenced the morphology of the fungal pellets, and assisted in controlling excess biomass growth. This study shows that fungal bioreactors can handle fluctuating loads of aqueous-phase SeO32−, while simultaneously offering the possibility to synthesize elemental selenium under long-term operations.