Saturated Hydraulic Conductivity of Bioretention Media with Municipal Waste Incinerator Bottom Ash

The purpose of this experiment was to determine if incinerator bottom ash from municipal waste can be an acceptable replacement for sand in bioretention media. The replacement of bottom ash for sand in bioretention media would be a sustainable practice because it would lower ash disposal fees for the generator, reduce the volume of ash sent to landfills, reduce the need for dredging river sand, and provide a beneficial use for a waste material. The saturated hydraulic conductivity was evaluated for five mixed medium sets, which included a control that represented a typical bioretention medium. The control was a mixture of 75% sand and 25% compost (by volume). The experimental media included two sets of mixtures of ash and compost (50% and 75% ash by volume) and two sets of mixtures of ash and wood fines (50% and 75% ash by volume). To determine the saturated hydraulic conductivity of the different mixed medium sets, 18 bioretention columns were fabricated and tested. The hydraulic conductivity of the experimental media ranged from approximately 4 to 73 cm per hour (1.5 to 29 in. per hour). Based on this study, the replacement of incinerator bottom ash for sand in bioretention media would satisfy drainage requirements because all sets resulted in a hydraulic conductivity of greater than 2.54 cm per hour (1 in. per hour).