Qigang Chang is a Ph.D student in Environmental and Conservation Science Program at North Dakota State University. He received a Master of Science (2006) and a Bachelor Degree (2001) in Environmental Engineering from East China University of Science & Technology (ECUST), China. Currently, he is working on the project to develop a new adsorbent-GAC-NZVI to remove arsenic from drinking water. qigang.chang@ndsu.edu Phone: 701-231-8955

Development of GAC-NZVI Adsorbent for Arsenic Removal

Fellow: Qigang Chang

Advisor:  Dr. Wei Lin, Ph.D., Associate Professor, Department of Civil Engineering, North Dakota State University

Degree Progress:  Ph.D. in Environmental Science expected in December 2009

Research:

The occurrence of arsenic in groundwater is of great concern because arsenic is extremely toxic and contributes to skin, bladder, and other cancers. Many areas have been identified in the USA with arsenic problems in groundwater. A review of water samples from 17,000 wells suggested that around 5% exceed 20 µg/L. The arsenic level is approximately 24 µg/L in all three wells supplying drinking water at Oakes and at around 40 µg/L at Devils Lake, North Dakota.

In 2001, the USEPA revised its drinking water maximum contaminant level (MCL) for arsenic downwards from 50 µg/L to 10 µg/L, which presented a major challenge for the existing water supply systems to comply with the new regulation, especially the rural small community systems which until recently had few regulation requirements.

Methods currently employed for removing arsenic from groundwater include coagulation, chemical precipitation, adsorption, membrane process, and ion exchange. Coagulation and precipitation could effectively reduce arsenic from water with high arsenic concentration (>100mg/L); however, residual concentration exceeds 10 µg/L. Membrane techniques significantly reduces arsenic to below 5 µg/L but it is expensive and susceptible to fouling by fine particles. Ion exchange uses costly resins. Iron-based materials was extensively studied to treat arsenic from groundwater and showed promising adsorption capacity. But, due to the small surface area of iron filings, the reaction rate is often limited by availability of active sites. In addition, mobility of arsenic on iron based material could be caused by microbial reduction of arsenate, reductive dissociation of iron oxyhydroxide phases and competition of solutes of sorption sites on iron oxides. Iron corrosion also may release soluble iron and small iron particles into water cause color problems.

Granular Activated Carbon (GAC) is an excellent stable adsorbent widely used in water treatment process, especially for organic contaminants. But GAC alone only exhibits limited adsorption capacity to arsenic. Iron modified GAC enhanced the adsorption capacity for arsenic pronouncedly. However, there is a serious problem related with the stability of iron on GAC. Part of iron preloaded on GAC may be peeled away by external force to cause problems again when used. In addition, effective iron content is low.

New affordable technology is needed to treat arsenic in drinking water to comply with new regulation. The proposed research hypothesizes that GAC-NZVI (nano zero valent iron) could be synthesized with desired content of nano iron which are stable and highly reactive. GAC-NZVI could be a promising adsorbent to treat trace arsenic in drinking water by inheriting advantages from GAC and NZVI while avoid their drawbacks. GAC-NZVI could be directly used in existing GAC fix-bed system without additional extension and separation. Organic compounds may still have access to the huge specific surface of GAC so that GAC-NZVI will retain the ability to remove odor, taste, and color.

Project Objectives:

The primary goal of this research is to develop GAC-NZVI adsorbent to treat arsenic to meet current stringent drinking water standard at an affordable cost for rural communities in North Dakota. The specific objectives are as follows:

1. To develop a method to synthesize GAC-NZVI adsorbent with desirable characteristics for arsenic removal;
2. To determine the adsorption capacity and kinetic for arsenic removal using GAC-NZVI adsorbent;
3. To study the mechanisms of arsenic removal and factors that affect arsenic removal capacities and efficiency by GAC-NZVI adsorbent; and
4. To predict the performance of the GAC-NZVI adsorbents at various chemical conditions through model simulations.

Experimental and analytical studies will be carried out to achieve the above objectives. Groundwater samples from several locations of North Dakota, including Lidgerwood, Richland and Oakes, will be used to evaluate the performance of GAC-NZVI.

Progress :

So far, an extensive literature review has been done and current methods to synthesize nano iron particles have been evaluated. A well understanding of current research built up a solid base for proposed research. Preliminary experiments were carried out at summer of 2007 to prove critical concept that GAG-NZVI could be synthesized. Two new methods were developed to impregnate iron on GAC. In addition, a new experimental technique was developed to prevent the loss of iron during the following nano iron synthesis process.

Significance:

GAC-NZVI will be a promising adsorbent that could be used to remove arsenic from drinking water at existing facilities without further expansion. The GAC-NZVI adsorbent could meet the stringent drinking water standard of arsenic at affordable cost and help rural communities of North Dakota to comply with federal regulations. In addition to the benefits to North Dakota, sharing of knowledge from this research will benefit the environmental community as a whole and encourage additional research to create new technologies by combination of latest technologies with conventional technologies.