USING ACTIVATED CARBON TO ENHANCE THE VOCS AND HEAVY METALS REMOVAL OF A POROUS ASPHALT PAVEMENT SYSTEM

Abstract

Two different porous asphalt pavement systems (PAPS) were designed to enhance the removal of VOCs (dichloromethane and toluene) and heavy metals (cadmium, copper and lead) from roadway runoff. These two PAPS utilized granular activated carbon (GAC) additions to the conventional PAPS. One PAPS, the CPP system (carbon in porous pavement), had GAC added directly to the top porous asphalt mix, and the other PAPS, the CCA system (carbon in coarse aggregates), had GAC added to the sub-base filter course below the porous asphalt layer. The removal of selected VOCs and heavy metals through the CPP and the CCA systems was measured and compared to a conventional PAPS. The results show that the addition of GAC into the top porous asphalt layer and the sub-base filter course layer enhanced the overall porous asphalt pavement contaminants removal capability. The addition of GAC to the sub-base filter course layer resulted in higher removal efficiencies for all of the constituents tested in this study. The CPP system is capable of removing on average 83% of dichloromethane, 95% of toluene, 71% of cadmium, 66% of copper, and 73% of lead. The CCA system resulted in the average removal of 99% of dichloromethane, 100% of toluene, 95% of cadmium, 76% of copper, and 75% of lead from a synthetic roadway runoff. The CCA system was able to control the effluent concentrations of all of the contaminants (dichloromethane, toluene, cadmium, copper and lead) to meet the US EPA MCLs (Maximum Contaminant Levels). Even though the same amount of GAC was added into the two systems some of the GAC in the CPP system could have been coated by the asphalt binder during the construction process which would reduce the iii effective GAC surface area available for adsorption and thus reduce the effectiveness of contaminant removal.