Monday, June 18, 2007 - 9:35 AM
Snake River (Boise Centre on the Grove)
55

Simulation of in-situ arsenic remediation in groundwater: iron precipitation and arsenic immobilization by batch and column experiments

Solomon W. Leung, Idaho State University, Pocatello, ID, Songqiao Chen, Idaho State University, Pocatello, ID, Golam M.I. Chowdhury, Yale University School of Medicine, New Haven, CT, and James C.K. Lai, Idaho State University, Pocatello, ID.

U.S. Environmental Protection Agency (EPA) has reduced arsenic drinking water standard from 50 parts per billion (ppb) to 10 ppb and the new standard compliance has been required since February 2006. The new standard may be costly for small treatment facilities in rural areas.

An innovative “treat-and-pump” method is reported in this study which may provide an inexpensive alternative for these small facilities, or for many communities in developing countries where arsenic in drinking water is a major public health concern.

This inventive technique includes three major steps: 1. Ferric ion is injected into a well and precipitate out as hydrous ferric oxide (HFO) by hydrolysis. 2. Arsenic in groundwater is adsorbed onto HFO and is immobilized locally. The sorption will significantly reduce dissolved arsenic concentration in the groundwater and “clean” water will be produced thereafter. 3. Arsenic is remobilized when HFO reaches maximum sorption capacity for arsenic species through either aquifer acidification or alkalization. Once arsenic is released into the water phase again, the arsenic rich groundwater will then be pumped out and arsenic will be removed from the groundwater aquifer permanently.

Both batch and column experiments were conducted to simulate the geochemical reactions and dynamic processes involved in actual treatment situation. Column experimental design based on results from batch experiments showed that arsenic could be absorbed onto HFO in a flowing groundwater environment and HFO could reduce arsenic from 100 ppb to lower than 10 ppb.