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 2+ ) from diluted actual mine wastewater (DW) and Cd 2+ -contained simulated wastewater (SW), with a uniform Cd 2+ 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 2+ removal. The Cd 2+ 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 2+ removal efficiency (90%) in the DWA in comparison to the SWA. The Cd 2+ assimilation by M. aeruginosa and Cd 2+ 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 2+ removal efficiency in DWB increased significantly, and this was attributed to the increased abundance of non-living cells and enhanced bioretention of Cd 2+ . The results revealed that continuous K + supplementation enhanced the Cd 2+ removal efficiency in the M. aeruginosa -based PBR jointly by prompting algal cell growth, Cd 2+ assimilation and biosorption , as well as Cd 2+ retention on the algal cells.