Iron Nanoparticles for In Situ Groundwater Remediation of Chlorinated Organic Solvents in Taiwan

A 200-m 2 pilot-scale field study successfully demonstrated that palladized nanoscale zero-valent iron (NZVI) is capable of remediating groundwater contaminated with a variety of chlorinated organic solvents including vinyl chloride (VC), dichloroethanes and dichloroethylenes in southern Taiwan. Major contaminant is VC that has a concentration ranging from 10 to 5000 µg/L. The concentration distribution is depth-dependent at the site where contaminant concentrations increased with depth. A total iron mass of about 20 kg on-site synthesized NZVI (Pd 0.05 wt%) suspended in 8,500 L water was injected via gravity into the sandy aquifer. Thirteen multi-level monitoring wells allowing to collect samples from three different depths (6, 12, 18 m) were installed. For a monitoring period of 3 months, a spatial and temporal decrease in VC concentrations was observed. The degradation efficiency was greater than 90% at both upper and middle layers but was about 20-85% at the bottom layer. Oxidation-reduction potential (ORP) measurements indicated a homogeneous reducing condition (ORP -450 ∼ -280 mV) was achieved in the testing field. Analysis of total iron concentrations found iron was mainly trapped at the upper layer. NZVI-enhanced biodegradation was observed.