Christopher Capecchi 2011

Fellow: Christopher Capecchi (work completed by a few other graduate and undergraduate students since Mr. Capecchi quit the Fellowship half way through)
Adviser: Achintya Bezbaruah

Arsenic Contaminated Groundwater Remediation by Entrapped Nanoscale Zero-Valent Iron

In response to the significant threat arsenic presents, the United States Environmental Protection Agency (USEPA) drastically modified the maximum contaminant level (MCL) for arsenic in drinking water from 50 μg/L to 10 μg/L in 2006. Even at 10 μg/L the world health organization (WHO) estimates a 0.2% chance of developing cancer in humans. Millions are presently at risk due to high arsenic levels in drinking water. Acute and chronic arsenic exposure from drinking water has been reported in many countries, most of which have large proportions of drinking water contaminated with high concentrations of arsenic (total As 50 μg/L). The United States Geological Survey (USGS) analysis of 30,000 random groundwater samples across the United States found that approximately 10% of sites had arsenic concentrations in excess of 10 μg/L. Moreover, arsenic is second only to lead (Pb) as the most commonly found hazardous contaminant at Superfund Sites. In Southeastern North Dakota more than 25% of groundwater samples contain arsenic at levels in excess of 10 μg/L. The U.S. EPA conducted a five year review (2004-2008) to analyze the remedial action implemented in Southeastern North Dakota. Approximately 375 wells in the 26 townships (about 568 square miles) were sampled and it was found that more than 84% samples have the arsenic concentration above the MCL. This presents an unacceptable risk of cancer and adverse health effects to the residents who depend upon water from the aquifer. By entrapping NZVI within a biopolymer (Ca-alginate) the overall contact time with contaminants will be prolonged, allowing individual particles to react more efficiently. By optimizing critical parameters such as NZVI dosage and pH, the waters can be effectively remediated below the USEPA arsenic MCL (10 μg/L). The objective of this research is to determine the treatability of arsenic by entrapped NZVI. The specific objectives of the study are: 1) Conduct entrapped NZVI treatability batch studies with various As5+ and As3+ concentrations. 2) Examine the effects of individual ions (which are present in groundwater) on the arsenic removal (by entrapped NZVI) reaction kinetics. 3) Characterize entrapped NZVI within Ca-alginate beads using X-ray 17 diffraction (XRD) and scanning electron microscopy (SEM) to understand the arsenic treatment mechanisms. 4) Perform entrapped NZVI treatability batch studies with actual arsenic contaminated groundwater.

This project explored aqueous arsenic removal using nanoscale zero-valent iron (NZVI) entrapped in calcium (Ca) alginate beads. The results from this study show great promise for entrapment technique as an advanced treatment technique for aqueous arsenic. Arsenic is a serious threat to human health and millions of people are affected by arsenic contamination in various parts of the world including the United States. The entrapment process reduces mobility of the nanoparticles by confining them within the polymer matrix and, thus, reducing the risk of post-treatment hazard by arsenic sorbed onto NZVI. Ca-alginate polymer is an excellent choice as an entrapment medium as it is non-toxic and has little solubility in water. In bench scale batch studies with initial As(V) concentrations of 1-10 mgL-1, ~ 80-100% arsenic removal was achieved within 2 hours. While the reaction kinetics differ between bare and entrapped NZVI, the overall reductions of arsenic are comparable. Surface normalized arsenic reduction reaction rate constants (ksa) for bare and entrapped NZVI were 3.40-5.96x10-3 and 1.90-4.43 x10-3 L m-2 min-1, respectively.

Graduate student who originally worked on this project was Christopher Capecchi, and later two other graduate students and a few undergraduate students participated in this project. One peer reviewed paper (2011) has been published in the Proceedings of ASCEEWRI World Environmental and Water Resources Congress 2011, and another paper has been submitted (2012) to a referred journal for possible publication. In addition two posters were presented on the research (both in 2010).

Publication:

Capecchi, C.; Bezbaruah, A. Novel Alginate Entrapped Nanoparticles for Groundwater Arsenic Remediation, Proc. World Environmental and Water Resources Congress 2011, pp. 3389-3395, 2011 (also oral presentation).

Achintya Bezbaruah
Civil & Environmental Eng.
Office: Civil/Ind Eng 201G
Telephone: 701-231-7461
Email: a.bezbaruah@ndsu.edu