Decrease of non-point zinc runoff using porous concrete

The use of porous concrete columns to decrease the amount of zinc in stormwater runoff is examined. The concentration of zinc in a simulated stormwater fluid (zinc acetate solution), fed through concrete columns (∅10 × 10 cm) decreased by 50–81%, suggesting physical adsorption of zinc by the porous concrete. We propose the use of porous concrete columns (∅50 × 10 cm) as the base of sewage traps. Longer-term, high-zinc concentration monitoring revealed that porous concrete blocks adsorb 38.6 mg cm−3 of zinc. A period of no significant zinc runoff (with an acceptable concentration of zinc in runoff of 0.03 mg L−1, a zinc concentration equal to the Japanese Environmental Standard) is estimated for 41 years using a 1-ha catchment area with 20 porous concrete sewage traps. Scanning electron microscopy of the porous concrete used in this study indicates that the needle-like particles formed by hydration action significantly increase zinc adsorption. Evidence suggests that the hydrant is ettringite and has an important role in zinc adsorption, the resulting immobilization of zinc and the subsequent effects on groundwater quality.