Performance of a prb for the remediation of acidic groundwater in acid sulfate soil terrain

Contaminated groundwater resulting from pyrite oxidation of acid sulphate soils (ASS) is a major environmental problem in coastal Australia. A column test was carried out for an extended period with recycled concrete to study the efficiency of the reactive materials for neutralising acidic groundwater. Results show that the actual acid neutralisation capacity of the recycled concrete could decrease to less than 50% of the theoretical value due to armouring effects. Nevertheless, the performance is good as a spot treatment in Acid Sulphate Soil Terrain utilising a near-zero cost waste product. Based on the test results and site characterisation, a PRB with recycled concrete was designed and installed in ASS terrain on the Shoalhaven River floodplain, southeastern, Australia in October 2006. The performance of the PRB was studied over two and half years to assess the potential of recycled concrete (i) to neutralise the groundwater acidity and (ii) to remove the dissolved heavy metals such as iron and aluminium from in situ acidic groundwater. To date, performance monitoring of the PRB shows that recycled concrete can successfully improve the pH of groundwater from acidic to mildly alkaline. In addition, it successfully removes groundwater iron and aluminium. Results reported here also reveal a slow decrease in the performance of the PRB due to armouring effects probably caused by precipitation of iron and aluminium on the surface of the reactive recycled concrete materials.