Assessment of pyrene adsorption on biochars prepared from green infrastructure plants: Toward a closed-loop recycling in managing toxic stormwater pollutants

Abstract

Recently biochar is receiving increased attention as an alternative filter medium for enhanced stormwater management. This study attempted to recycle plants harvested from the upper green infrastructure (GI) component for reuse in the lower GI component as a filter medium. Dawn redwood (DR) and bridal wreath (BW) were harvested and converted to biochar. Leaves and branches of each plant species were pyrolyzed at 300 and 500 degrees C and the prepared biochars were characterized and evaluated for their adsorption capacity of pyrene, one of the major polycyclic aromatic hydrocarbons (PAHs) in urban stormwater runoff. The biochar made from DR leaf at 300 degrees C showed the highest pyrene adsorption efficiency and was well-fitted with pseudo-second order kinetics and Freundlich isotherm. The first biochar regeneration cycle demonstrated that both thermal and solvent extraction showed high pyrene adsorption efficiency recovery with values of 98.8 and 98.0%, respectively. The relationships between surface properties and adsorption capacities of biochar for PAHs and heavy metals, the two major toxic stormwater pollutants, were further investigated using data pooled from the existing studies. The literature data analysis showed that biochars produced at a lower pyrolysis temperature (similar to 300 degrees C) can efficiently remove PAHs and heavy metals due to higher hydrophobic interactions and higher cationic exchange capacity, respectively. This study suggests the potential feasibility of closed-loop recycling of GI plants for sustainable stormwater treatment and carbon sequestration.