Date of Award
Program or Major
Master of Science
M Robin Collins
Arsenic contamination in drinking water is a worldwide public health concern associated with serious acute and chronic health effects. Listed as a "Group A" human carcinogen, arsenic is regulated in drinking water at 0.010 mg/L by the U.S. Environmental Protection Agency (EPA). Arsenic contamination stems from both natural and anthropogenic sources, and areas with high levels of arsenic can be found in countries throughout the world, including the United States (Smedley and Kinniburgh 2002). In the past decade, interest in iron-based sorbents, particularly zero-valent iron (ZVI), has developed for their use as an arsenic-removal technique due to the lack of research and the possibility for an inexpensive, efficient, locally available, and simple adsorbent material. Previous studies, including several at UNH, have indicated that ZVI can be very effective in the removal of arsenic by adsorption (Hadnagy 2004, Le Roux 2005, Pepler 2009).
The primary focus of this research was to investigate innovative separation processes for ZVI in an arsenic treatment system as well as evaluate the effect of water quality and operational conditions on iron dissolution and adsorption kinetics in an arsenic treatment system utilizing ZVI. The study also investigated the potential for a magnetite-based byproduct material to be used for arsenic adsorption.
The ZVI separation processes included a bench-scale assessment of magnetic separation processes as well as a pilot-scale assessment of diatomaceous earth (DE) precoat filtration. The high-gradient magnetic separation (HGMS) system showed optimistic results in its bench-scale application as a ZVI separation system, and the DE precoat filtration strategy successfully removed ZVI from a pilot-scale arsenic treatment scheme. The arsenic treatment system utilizing DE precoat filtration for ZVI separation achieved 30 to 40% arsenic removals while maintaining dissolved iron concentrations below the EPA's secondary standard of 0.3 mg/L. Arsenic removals improved with increased contact time and ZVI dose, and iron dissolution issues from past studies were alleviated by increasing pH conditions from 6 to 7 within the system.
Furthermore, arsenic adsorption kinetics were found to be effected by oxidant type and ZVI pretreatment time in a bench-scale study, where increased reaction kinetics were observed with the use of stronger oxidants and shorter ZVI pretreatment times. It must be noted that shorter pretreatment times did result in higher dissolved iron concentrations in the system. Anion competition by fluoride was also assessed. Fluoride was not found to be sorbed by ZVI, nor did it compete with arsenic adsorption by ZVI. Finally, the magnetite-based byproduct material was not found to be an effective sorbent for arsenic treatment.
Little, Nathan H., "Assessing innovative zero-valent iron separation processes in an arsenic treatment scheme" (2011). Master's Theses and Capstones. 688.