Potassium supplement enhanced cadmium removal in a Microcystis aeruginosa photobioreactor: Evidence from actual and simulated wastewater.

In this study, a Microcystis aeruginosa-based photobioreactor (M. aeruginosa-based PBR) was developed for the removal of cadmium (Cd) from diluted actual mine wastewater (DW) and Cd-contained simulated wastewater (SW), with a uniform Cd concentration of 0.5 mg/L. For the DW and SW, both K -abundant (DWA & SWA) and K-insufficient (DWB & SWB) treatments were conducted. It was found that continuous supplementation of K benefited Cd removal. The Cd removal efficiency in SWA reached 70% during the 41 days of operation, which was 20% higher than that in the SWB. The K addition triggered great higher Cd removal efficiency (90%) in the DWA in comparison to the SWA. The Cd assimilation by M. aeruginosa and Cd retention on M. aeruginosa surface were the primary processes involved in the PBR system. The K starvation triggered a 45% and 43% loss of M. aeruginosa biomass in the DWA and the DWB, respectively. Hence, the Cd removal efficiency in DWB increased significantly, and this was attributed to the increased abundance of non-living cells and enhanced bioretention of Cd. The results revealed that continuous K supplementation enhanced the Cd removal efficiency in the M. aeruginosa-based PBR jointly by prompting algal cell growth, Cd assimilation and biosorption, as well as Cd retention on the algal cells.