Using Permeable Reactive Barriers to Remediate Heavy Metal-Contaminated Groundwater through a Laboratory Column Experiment

Recently, groundwater sources are being polluted by various activities such as agriculture, livestock, decentralized wastewater treatment systems and acid rain. Groundwater can also be polluted by landfill leachate, sewage, mine tailings, non-engineered deep well disposal of liquid waste and seepage from industrial waste lagoons. There are many studies reported contaminated groundwater remediation using Permeable Reactive Barrier systems (PRBs) and many countries happen to use this system to eliminate groundwater contaminants. This study reports the outcomes of the batch and the column test experiments conducted to evaluate the removal efficiency of four heavy metals: Cd(II), Cu(II), Fe(II) and Pb(II) using five locally available reactive materials (in Sri Lanka) with grain sizes less than or equal to 2.0 mm: Red Soil (RS), Laterite Soil (LS), Bangadeniya Soil (BS), Burnt Clay Tile (BCT) and Coconut Shell Biochar (CSB) as PRB materials. Seven columns (A-G) were filled with the reactive material of CSB (column E) and reactive material mixtures; RS + CSB (column A), LS + CSB (column B), BCT+CSB (column C), BS + CSB (column F), RS + LS (column G), with a weight ratio of 50:50 and RS + BCT + CSB (column D) with a weight ratio of 100/3:100/3:100/3. The results showed that the reactive materials filled in column A, B, D, F and G removed the metal concentrations, with a removal efficiency of over 90%, except Cd in the column with BCT + CSB mixture. Considering both the removal efficiency and the hydraulic conductivity of the columns, materials in column A, B, D and F are more effective than the others as PRB adsorbents for heavy metal remediation, while columns C and E have lower removal efficiency.