Assessing the Role of Biochar in Heavy Metal Leaching Risk from Construction and Demolition Waste

This study investigates how pulverized wood-derived biochar affects leaching and release behavior of Chromium (Cr), Copper (Cu), and Nickel (Ni) from construction and demolition waste (CDW) towards groundwater. CDW constitutes a large portion of total waste generation in both developed and developing countries, prompting attention due to its substantial volume, resource implications and environmental risks. Involvement of dissolved organic carbon (DOC) and turbidity in mobilization and release of heavy metals in pulverized biochar-amended CDW has been addressed for the first time in this research. Leaching and release of heavy metals from CDW was evaluated using column leaching test. Wood-derived biochar, produced at temperatures up to 750°C, was incorporated into columns. Leachates, collected at regular intervals, were analyzed for heavy metals using inductively coupled plasma-mass spectrometry (ICP-MS). Results indicated initial high mobilization followed by rapid decline in leached concentrations of heavy metals. Biochar incorporation reduced cumulative release of heavy metals from CDW into the aqueous phase, with a more pronounced impact for Cu and Ni. Higher biochar content led to increased initial mobilization of Cr, Cu, and Ni. Positive correlations were observed between leached concentrations of Cr, Cu, and Ni from CDW with both DOC and turbidity, with DOC making a more significant contribution in pulverized biochar-amended CDW. Although biochar demonstraed promise in reducing heavy metal leaching from CDW, its efficacy plateaued at higher application rates. This highlights the necessity to optimize biochar dosage for immobilizing heavy metals in CDW and safeguarding groundwater.