Impregnated calcium-alginate beads as floating reactors for the remediation of nitrate-contaminated groundwater

In this study, calcium-alginate beads impregnated with nano zero valent iron (NZVI), magnetite nanoparticles (MNP), and powdered activated carbon (PAC) were synthesized, as they were mixed with calcium carbonate powders in sodium alginate solution and reacted with calcium chloride and citric acid. Optical and scanning electron microscopy (SEM) images showed that the nanoparticles were uniformly embedded, and gas bubbles formed, in the polymeric beads. Comparative experiments were carried out as the nanoparticles were dosed, in original (bare) or immobilized form (embedded in the beads), into 100 mg/L nitrate-nitrogen (NO₃-N) solutions at 5, 10, and 15 g/L. In 48 h, each gram of immobilized NZVI in the beads were found to reduce 4.3–9.6 mg NO₃-N to ammoniacal-nitrogen (NH₄-N). Up to 47.8% NH₄-N resulted from NO₃-N reduction was immobilized by PAC in the beads. These results demonstrated the effectiveness of using the beads for in-situ removal of nitrate, potentially producing an alternative technique to treat nitrate contaminated waters under anaerobic condition.