Chemistry and microbiology of permeable reactive barriers for in situ groundwater clean up

Permeable reactive barriers (PRBs) are receiving a great deal of attention as an innovative, cost-effective technology for in situ clean up of groundw ater contamination. A wide variety of materials are being proposed for use in PRBs, including zero-valent metals (e.g., iron metal), humic materials, oxides, surfactant-modified zeolites (SMZs), and oxygen- and nitrate-releas ing compounds. PRB materials remove dissolved groundwater contaminants by i mmobilization within the barrier or transformation to less harmful products . The primary removal processes include: (1) sorption and precipitation, (2 ) chemical reaction, and (3) biologically mediated reactions. This article presents an overview of the mechanisms and factors controlling these indivi dual processes and discusses the implications for the feasibility and long- term effectiveness of PRB technologies.