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

•Ca-alginate beads were impregnated with iron and activated carbon powders.•The impregnated beads were tested for their ability to transform NO3-N.•Each gram immobilized Fe(0) reduced 4.3–9.6 mg NO3-N to NH4-N in 48 h.•Up to 47.8% NH4-N was adsorbed by activated carbon powders in the beads.