SPECIAL ISSUE: ENVIRONMENTAL NANOMATERIALS Arsenic Removal by Nanoscale Magnetite in Guanajuato, Mexico Jesse Walter Farrell, 1, * John Fortner, 2 Sarah Work, 3 Carolina Avendano, 4 Natalia I. Gonzalez-Pech, 4 Rafael Za ´ rate Araiza, 5 Qilin Li, 3 Pedro J.J. A ´ lvarez, 3 Vicki Colvin, 4,6 Amy Kan, 3 and Mason Tomson 3 1 Water Management, Schlumberger, Houston, Texas. 2 Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri. 3 Department of Civil and Environmental Engineering, Rice University, Houston, Texas. 4 Department of Chemistry, Rice University, Houston, Texas. 5 CITAG, Guanajuato, Mexico. 6 Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas. Received: November 1, 2013 Accepted in revised form: April 18, 2014 Abstract Increasingly, cities in Latin America are recognizing the importance of drinking water quality on public health. A water assessment of Guanajuato, Mexico, and surrounding areas indicated naturally occurring arsenic in some wells above the Mexican drinking water standard of 25 lg/L and the World Health Organization recommen- dation of 10 lg/L. This initiated a collaborative effort with the city to evaluate a new arsenic removal method using high surface area magnetite sorbents. Nanoscale (20 nm) magnetite particles, previously shown to ef- fectively adsorb arsenic in batch systems, were packed in sand columns to create a continuous treatment process. Design and operating variables were evaluated to confirm that magnetite-to-sand ratio and residence time most significantly affected arsenic breakthrough profiles. Subsequently, a pilot column with 456 g (ca. $2.50 USD) of a commercially available, food-grade magnetite (98 nm effective particle diameter) from a pigment manufacturer demonstrated removal of the equivalent arsenic contained in 1,360 L of Guanajuato groundwater. Although pH reduction dramatically improved arsenic adsorption in batch isotherms, no im- provement in arsenic removal efficiency was observed when applied to pilot-scale, field columns in Guanajuato. Interference effects (e.g., from background silica) and changes to surface species over time may impact adsorption differently in column versus batch systems. Overall, this work represents one of the first pilot studies of a nanotechnology-enabled water treatment system, and it demonstrates the potential and additional chal- lenges for taking nanoscale magnetite or other highly researched nanomaterials into a complex full-scale setting. Key words: adsorption; arsenic; breakthrough; case study; column; drinking water treatment; Guanajuato; iso- therms; Mexico; nanomagnetite; nanotechnology; sand filtration Introduction A rsenic is a semi-metal that occurs naturally in the environment and as a by-product of industrial activity (Plant et al., 2005). The presence of arsenic in drinking water is a widespread problem in many developing regions. Long- term exposure to arsenic can result in hyperkeratosis, skin lesions, and cancer of the bladder, lungs, kidneys, and skin. There is some evidence that elevated exposure to arsenic increases risk of Type 2 diabetes (Navas-Acien et al., 2008), which is particularly concerning Mexico where diabetes may cost the Mexican government three-quarters of its total health care spending annually (Phillips and Salmeron, 1992). City officials in Guanajuato, Mexico, provided a test-bed site for researchers with the Center for Biological and En- vironmental Nanotechnology (CBEN) at Rice University to develop nanomaterial-based water treatment technologies suited to address water quality needs in Guanajuato. Heavy metal contamination of their water supply was a concern due to nearby silver and gold mining activity. Arsenic concen- trations as high as 33 lg/L in Guanajuato and 266 lg/L in surrounding towns were observed from municipal ground- water wells. In response to these findings, Guanajuato offi- cials agreed to support a field trial of a nanomagnetite-based filter capable of removing arsenic from their groundwater. This work represents one of the first case studies to evaluate a nanotechnology-enabled conventional treatment process for water supply in a developing country. We dem- onstrate under real-world conditions that augmenting sand filters with nanoscale food-grade magnetite could benefit *Corresponding author: Oilfield Water Management, Schlum- berger, 5599 San Felipe, Houston, TX 77056. Phone: 281-285- 4390; Fax: 281-285-1927; E-mail: jfarrell01@slb.com ENVIRONMENTAL ENGINEERING SCIENCE Volume 31, Number 7, 2014 ª Mary Ann Liebert, Inc. DOI: 10.1089/ees.2013.0425 1