FERRATE [FE(VI)]-DRIVEN REMEDIATION OF ARSENIC-CONTAMINATED GROUNDWATER: A SCALED-UP REACTOR STUDY WITH CONTAMINATED GROUNDWATER AND AQUIFER MATERIALS

Arsenic (As) contamination of groundwater poses a global and serious environmental concern. Advanced environment-friendly and economical remediation technologies are in high demand for effective removal of As from contaminated groundwater. The objective of this study was to demonstrate feasibility and technical effectiveness of ferrate [Fe(VI)] - an emerging “green” oxidant - for remediation of As-contaminated groundwater and aquifer materials in a pilot scale tank reactor under flow through conditions. As(III) was expectedly oxidized to As(V) by Fe(VI) and subsequently adsorbed onto the iron precipitates (the final product of Fe(VI) reduction). Tracer tests were performed to study the hydraulic properties of aquifer materials. Tracer (Br^-) breakthrough data were plotted against time to determine T₁₀ (4.50 h), T₅₀ (8.37 h), and T₉₀ (12.40 h) in the tank reactor. Experimental data best fit a sigmoid, 3-parameters equation (R² = 0.999). Thereafter, pilot scale reactor tank tests were conducted to identify key operating factors affecting As(III) removal efficiency in an experimental setup approximating actual field conditions. Four operating factors were tested, including initial pH (5.0 and 7.0), molar ratio of Fe(VI) to initial As(III) ([Fe(VI)]:[As(III)]₀) (1:100 and 1:200), initial As(III) concentration (1 mg/L), and Fe(VI) injection flow rate (1.5 and 3 mL/min). Results showed that Fe(VI), at a dose of ([Fe(VI)]:[As(III)]₀) = 100 and 200 removed 98.9 and 99.1 % As(III) at a ferrate addition rate of 1.5 mL/min, and 99.02% and 99.66% As(III) at a ferrate addition rate of 3 mL/min. No significant difference (p=0.001) in As removal was observed among the different treatment conditions, suggesting that a low ferrate dose and a low injection rate sufficiently guaranteed effective removal. This study demonstrated that ferrate (VI)-driven remediation may be a viable “green” alternative for cleanup of As from contaminated aquatic systems.