Evaluation of Biochar-Entrained Porous Concrete for Heavy Metal Removal from a Synthetic Stormwater

Abstract

This study evaluated the potential of biochar-entrained porous concrete (BEPC) to remove selected heavy metals from a synthetic stormwater. The primary objective of the study was to determine if replacement of cement with biochar on a selected dry weight basis (1%, 2% and 4%) increased removal of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) from a synthetic stormwater compared to the control (0% biochar). All treatments were tested at four contact times (CT) to evaluate the impact of contact time on heavy metal removal in a BEPC system. The contact times evaluated were 0, 5, 10 and 15 minutes. Compressive strength, porosity and infiltration rate were evaluated along with three water quality parameters (pH, alkalinity and hardness) to help explain metal removal dynamics. Twelve 10.16 cm diam x 20.32 cm high cylinders were used to cast test specimens (3 replicates each treatment). Results indicated that cadmium removal was highest at 57% at 15 min CT in the 4% biochar treatment and copper and lead removals were both maximum at moderate biochar incorporation (2%). Cu and Pb removal reached 72% and 86% at 15 min CT, respectively while chromium removal was observed to depend more strongly on contact time than on biochar treatment. Zinc was observed to have the weakest response to biochar treatment of the five heavy metals tested. Across all heavy metals, the 2% biochar treatment showed the highest overall removal performance at 38-57 % removal of Cd, 47-74 % removal of Cr, 43-72% removal of Cu, 62-86% removal of Pb and 17-38% removal of Zn. Multiple linear regression models were developed to evaluate the influence of biochar treatment, contact time, and selected water quality parameters on heavy metal removal. These models helped explain the factors controlling removal performance and provided a framework for predicting and interpreting treatment behavior under different experimental conditions. Overall, this research indicates that biochar-entrained porous concrete (BEPC) can perform as a multifunctional stormwater treatment material and that the quantity of biochar along with water chemistry changes within the BEPC system influence heavy metal removal.