Microbial Anoxic Oxidation of Arsenite Lily Milner Chemical

Microbial Anoxic Oxidation of Arsenite Lily Milner Chemical and Environmental Engineering, The University of Arizona 4/19/08 Acknowledgements: Dr. Reyes Sierra, Dr. Jim Field, Alex Sun, Estephania Marcos

Arsenic Federal standard for Arsenic in drinking water : 10 microgram/L Inorganic Sources o. Wood Treatment o. Pesticides o. Medicines o. Mining Organic Sources o. Volcanic Activity o. Sea Organisms o. Weathering of Rocks Health Effects o o Skin Lesions Lung, Kidney Cancer Diabetes Cardiovascular Disease

Arsenic Contamination in the US http: //www. usgs. org

Two Common Species of Arsenic Found in The Environment Arsenite [As(III)] Arsenate [As(V)] OH—As—OH | OH O || HO-As-OH | OH o More Toxic o Less Toxic o Absorbs to few minerals o Absorbs to many minerals o Prevalent in anaerobic environments o Prevalent in aerobic environments

Redox Cycles of Arsenic and Iron & Their Interaction As(III) Oxidation Fe(II) Oxidation e--acceptor As(III) (O 2 , NO 3 -) e--acceptor As(V) e—donor (organic matter) As(V) Reduction As(V) Fe(III) Oxides As(V) (O 2 , NO 3 -) Fe(II) + As(V) e--donor Fe(III) Reduction

Microbial Process of Bioreactors 5 H 3 As. O 3 + 2 NO 3 - 5 HAs. O 4 -2 + N 2 + 8 H+ + H 2 O Influent o Gas Electron Donor • 6. 67 e-3 m. M As(III) • 0. 357 m. M Fe(II) o Electron Acceptor • 2. 5 m. M NO 3 o - Carbon Source • HCO 3 Influent Effluent Sand Bed

SF 1 SF 2 Reactor with As(III)/Fe(II) + nitrate Control reactor with As(III)/Fe(II) – No nitrate

Results For Iron Oxidation

Results for Arsenic Removal

Conclusions The microbial oxidation of Fe(II) and As(III) to Fe(III) and As(V) by chemolithotrophic denitrifiers can account for the difference in arsenic removal between the columns. The results show that microbial oxidation of Fe(II) and As(III) linked to denitrification decreases the environmental mobility of arsenic.