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

Arsenic Contamination in the US

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

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

Microbial Process of Bioreactors Influent o Electron Donor 6.67e -3 mM As(III) mM Fe(II) o Electron Acceptor 2.5 mM NO 3 - o Carbon Source HCO 3 - Sand Bed 5 H 3 AsO NO 3 -  5 HAsO N 2 + 8H + + H 2 O Gas Influent Effluent

SF1 Reactor with As(III)/Fe(II) + nitrate SF2 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.