Treatment of arsenic, heavy metals, and acidity using a mixed ZVI-compost PRB

A 30-month performance evaluation of a pilot permeable reactive barrier (PRB) consisting of a mixture of leaf compost, zerovalent iron (ZVI), limestone, and pea gravel was conducted at a former phosphate fertilizer manufacturing facility in Charleston, SC. The PRB is designed to remove heavy metals and arsenic from groundwater by promoting microbially mediated sulfate reduction and sulfide-mineral precipitation and arsenic and heavy metal sorption. Performance monitoring showed effective treatment of As, Pb, Cd, Zn, and Ni from concentrations as high as 206 mg L(-1), 2.02 mg L(-1), 0.324 mg L(-1), 1060 mg L(-1), and 2.12 mg L(-1), respectively, entering the PRB, to average concentrations of <0.03 mg L(-1), < 0.003 mg L(-1), < 0.001 mg L(-1), < 0.23 mg L(-1), and <0.003 mg L(-1), respectively, within the PRB. Both As(III) and As(V) were effectively removed from solution with X-ray absorption near edge structure (XANES) analysis of core samples indicating the presence of As(V) in oxygen-bound form and As(III) in both oxygen- and sulfur-bound forms. XANES solid phase sulfur analysis indicated decreases in the peak amplitude of intermediate oxidized sulfur species and sulfate components with increasing distance and depth within the PRB.