Exploring shared adsorption capacity and thermodynamics for simultaneous removal of microcystin and phosphorus via green sorption media in eutrophic water

Abstract

The recurrent events of harmful algal blooms due to an increase of nutrients in eutrophic water bodies have augmented concerns over the presence of cyanobacterial toxins, especially Microcystin. Microcystin-LR (MC-LR) is the most common cyanobacteria toxin, gaining focus in the literature for its effect on human health. The aim of this study is to investigate the simultaneous removal of MC-LR and phosphate via four green sorption media is the presence or absence of phosphorus or calcium ions and their shared adsorption capacity and thermodynamics to mimic eutrophic water condition in a karst environment (South Florida). The four green sorption media are known as: (1) CPS (clay, perlite, and sand), (2) ZIPGEM (Zero-valent-Iron and Perlite-Based Green Environmental Media), (3) BIPGEM-1 (Biochar-Zero-valent-Iron and Perlite-Based Green Environmental Media-1), and (4) BIPGEM-2 (Biochar-Zero-valent-Iron and Perlite-Based Green Environmental Media-2). Based on the MC-LR removal efficiency, BIPGEM-2 has the best performance, followed by BIPGEM-1, ZIPGEM, and CPS. In terms of simultaneous removal of phosphate ions and MC-LR, ZIPGEM achieves higher removals, ranging from 55 to 60%, followed by BIPGEM-2, BIPGEM-1, and CPS. The MC-LR adsorption capacity of BIPGEM-2 ranges from 16.9 to 29.49 μg·g−1 based on the Langmuir isotherm model under different influent conditions, whereas the MC-LR adsorption capacity of BIPGEM-1 in a dynamic environment is 1.19 μg·g−1 based on the Modified Dose Response model. The decrease in the adsorption capacity of BIPGEM-1 in a dynamic environment can be attributed to the presence of dissolved organic matter and inorganic ions, present in the influent water matrix. The influence of the water matrix is also observed in the isotherm studies because the presence of PO43− negatively impacts the removal efficiencies of MC-LR, whereas Ca2+ positively impacts the removal efficiencies of MC-LR. Similarly, the presence of MC-LR affects the PO43− adsorption capacity of the sorption media.