Compost: Potent biosorbent for the removal of heavy metals from industrial and landfill stormwater

Stormwater can be contaminated with heavy metals and low-cost solutions are needed to treat large amounts of water. This study was conducted to determine the viability of compost as an adsorbent in Nordic conditions to treat stormwaters. Metal ions chosen for this study were Cadmium(II), Copper(II), Nickel(II), Lead(II) and Zinc(II) and the observed order of adsorption affinities to compost is Lead(II)>Cadmium(II)>Copper(II)>Zinc(II)>Nickel(II). Surface area of compost was determined to be 2.14 m²/g. Removal of metal ions can be attributed to the compost surface chemical properties due to the –hydroxyl and carboxylic acid functional groups, confirmed by infrared spectroscopy. The zero-point charge of the compost was determined to be 6.53, which favours the adsorption of metal ions at neutral pH. Adsorption is kinetically fast, and it takes less than 10 min to reach equilibrium. Equilibrium data were analysed and Cadmium fits with Langmuir, Copper with linear and Nickel, Lead and Zinc with Fowler-Guggenheim isotherm. Thermodynamic study demonstrated the spontaneity of adsorption. The adsorption study at different pH levels revealed that compost neutralizes the solution during adsorption, so no further pH adjustment for treated stormwater is needed, and treated stormwater can be directly released into the water stream. The efficiency of the compost was also investigated for real stormwater, and it was found that compost adsorbent is very efficient for the removal of trace concentrations of metallic ions from real stormwater. Lower temperatures do not affect the adsorption process, so compost would be a great choice as low-cost adsorbent material for lower outdoor temperatures, especially in Nordic regions.