Weifang Chen, Jiying Zou, Min Jang, Fred S. Cannon, and Brian A. Dempsey

OBJECTIVES:

The objectives of this research were to (1) devise a technically viable and economically reasonable approach for removing arsenic from drinking water down to 10 ppb or less, (2) tailor activated carbon with iron in such manner as to extend its bed life for removing arsenic, and (3) enhance the iron solubilization and tailoring processes so as to render a robustness that is adaptable to a wide array of water compositions.

BACKGROUND:

Arsenic in drinking water is of environmental concern because it is a carcinogen. A new arsenic limit of 10 ppb became effective in 2006 for U.S. drinking water systems. This new regulation would make small public water facilities face heavy financial burdens unless less costly methods of arsenic removal are developed. There is an urgent demand for an economical, effective, and reliable technique that is capable of removing arsenic species to this new level.

HIGHLIGHTS:

1. Activated carbon modified by iron is a competitive media for arsenic removal from drinking water. This method takes advantage of the high affinity of iron for arsenic.

2. Iron-modified activated coupled with solubilizable iron could further extend the bed life for arsenic removal.

APPROACH:

The authors have explored several means of pre-tailoring GAC so as to extend its bed life for removing arsenic from water. These tests have mostly employed rapid small column tests (RSSCTs), which have used #200 x 400 mesh GAC in a 5.0 mm diameter by 13.5 cm long column with a 1 minute empty bed contact time. In the RSSCT experiments, the research team monitored the bed volumes of water that could be treated before the initial breakthrough of arsenic to above 10 ppb. For some of the tests herein, the authors conducted batch isotherm tests and kinetic test, and these generally used Rutland groundwater that had been spiked with a relatively higher level of arsenic.

RESULTS/FINDINGS:

The researchers developed an iron-preloaded media that can remove arsenic to below 10 ppb for 26,000−33,000 bed volumes (BV). When this iron tailoring has been coupled with solubilizing zero valent iron within the same bed, arsenic was removed to below 10 ppb for 43,000 BV. In prior work, it was observed that when the zero valent iron preceded the iron-tailored GAC, bed life could extend to 150,000 bed volumes. These tests employed Rutland, MA water, which contained 50-55 ppb As. As an integral part of this success, the researchers recently devised a means of forming hydrous ferric oxide (HFO) within the GAC pores, and this hydrous ferric oxide has a high affinity for arsenic. Manufacturing contacts, as part of their marketing studies, indicate that these are a cost-effective means of removing arsenic.

IMPACT:

Cost data provided by the industrial in-kind partner, Siemens Water Technologies, indicates that the cost of this iron-tailored GAC is quite cost-competitive with the conventional granular iron, titanium, and resin media that are now being sold. The unit price of the iron-tailored GAC is projected to be at the low end of the cost spectrum relative to these others, and the bed life is about comparable.

RESEARCH PARTNER:

This study was jointly funded by the Water Research Foundation and the U.S. Department of Energy through the Arsenic Water Technology Partnership. The report will also be published by WERC (a Consortium for Environmental Education and Technology Development at New Mexico State University).