Risk mitigation by waste-based permeable reactive barriers for groundwater pollution control at e-waste recycling sites

Permeable reactive barriers (PRBs) have proved to be a promising passive treatment to control groundwater contamination and associated human health risks. This study explored the potential use of lowcost adsorbents as PRBs media and assessed their longevity and risk mitigation against leaching of acidic rainfall through an ewaste recycling site, of which Cu, Zn, and Pb were the major contaminants. Batch adsorption experiments suggested a higher adsorption capacity of inorganic industrial byproducts [acid mine drainage sludge (AMDS) and coal fly ash (CFA)] and carbonaceous recycled products [food waste compost (FWC) and woodderived biochar] compared to natural inorganic minerals (limestone and apatite). Continuous leaching tests of sand columns with 10 wt% lowcost adsorbents were then conducted to mimic the field situation of acidic rainfall infiltration through ewastecontaminated soils (collected from Qingyuan, China) by using synthetic precipitation leaching procedure (SPLP) solution. In general, Zn leached out first, followed by Cu, and finally delayed breakthrough of Pb. In the worstcase scenario (e. g., at initial concentrations equal to 50fold of average SPLP result), the columns with limestone, apatite, AMDS, or biochar were effective for a relatively short period of about 20-40 pore volumes of leaching, after which Cu breakthrough caused noncancer risk concern and laterstage Pb leaching considerably increased both noncancer and lifetime cancer risk associated with portable use of contaminated water. In contrast, the columns with CFA or FWC successfully mitigated overall risks to an acceptable level for a prolonged period of 100-200 pore volumes. Therefore, with proper selection of lowcost adsorbents (or their mixture), wastebased PRBs is a technically feasible and economically viable solution to mitigate human health risk due to contaminated groundwater at ewaste recycling sites.