Enhancement of Heavy Metals Retention in Sandy Soil by Amendment with Fly Ash

Stormwater runoff from urban areas can transport a significant load of heavy metals. Thus, the metals retention capacity of filter media in stormwater infiltration systems, such as bioretention cells, is an important consideration. Batch sorption and column leaching experiments were conducted to determine the sorption of copper, lead, and zinc in three soils (Dougherty sand, Teller loam, and Slaughterville loam), fly ash, and fly ash/sand mixtures. Dougherty sand had the lowest heavy metals retention, while fly ash had the highest. The addition of fly ash to Dougherty sand greatly increased its heavy metals retention. Heavy metals transport in bioretention cells was modeled using a linear equilibrium, convection-dispersion transport model with parameters determined from laboratory columns. The modeling results indicated that a treatment layer of filter media with 1 m depth will remove heavy metals from stormwater for only 10 years if pure sand is used, but metals removal will continue for over 900 years if a fly ash/sand mixture is used.