Joon H. Min, Jiangzhao Zhang, Christian Tasser, Gil F. Crozes, and Janet G. Hering

OBJECTIVES:

The objectives of this project were to develop and evaluate single-use hydrogel adsorbent for the removal of arsenic from water and spent brine and demonstrate the minimization of spent hydrogel media volume for disposal.

BACKGROUND:

There is a need for cost-effective arsenic treatment technologies for small systems where minimal resources are available. Among the arsenic treatment alternatives, single-use media adsorption provides the simplest approach for treatment of arsenic at the wellhead, since it typically does not require additional chemicals, and minimizes the generation of arsenic-laden liquid waste, which is difficult to manage. Therefore, there is a need for innovative media to remove arsenic and minimize residuals for proper disposal.

HIGHLIGHTS:

The successful implementation of arsenic treatment entails not only the removal efficiency of arsenic, but also residual management. One of the innovative adsorbents that addresses these aspects of arsenic treatment is iron-doped, biopolymer-based hydrogel media, which showed removal capabilities for arsenic, chromium, and other oxyanions.

This report provides the performance of hydrogel media in treating a wide range of water sources, including groundwater, surface water, ion exchange brine, and reverse osmosis concentrate. The report compares the performance of the hydrogel media to three commercial media. In addition, test results on the dehydration property of the hydrogel media are also included.

APPROACH:

The project team conducted the following steps:

• Optimized and synthesized 11 variations of hydrogel adsorbent as single-use media

• Conducted bench-scale testing to demonstrate removal of arsenic by hydrogel media

• Compared the performance of hydrogel media to three commercially available media

• Tested the performance of hydrogel media to remove arsenic from the IX brine or the RO concentrate

• Determined the removal of other constituents, such as chromium, phosphate, etc., by hydrogel media

• Monitored the volume reduction of the hydrogel media when subject to dehydration

RESULTS/FINDINGS:

Most of the hydrogel media produced exhibited arsenic removal capacity for different sources of groundwater with various levels of arsenic speciation, chromium, silica, sulfate, phosphate, nitrate, perchlorate, and pH. Under the conditions tested, arsenic removal efficiency of hydrogel media was comparable to that of commercial media. A number of hydrogel media showed promise for arsenic removal in groundwater, with arsenic ranging from 15 to 540 μg/L.

Hydrogel media were effective at treating high levels of arsenic, up to 300 µg/L to concentrations below the detection levels from both the IX brine and the RO concentrate streams, with competing anions of 3 to 4 orders of magnitude higher than the concentration of arsenic. Also, with an initial chromium concentration of 1.6 mg/L in the IX brine, the hydrogel media showed 50 to 94 percent reduction of Cr(VI) under the conditions tested, with a significant amount of other anions such as nitrate, sulfate, alkalinity, etc. The reduction of Cr(VI) using the commercial media was less effective, showing only 20 to 30 percent removal. As such, the reduction of chromium in the IX brine by hydrogel media can be a promising application.

IMPACT:

An important aspect of this project was to evaluate the performance of innovative single-use media for arsenic application. This project presents alternative single-use media for arsenic, chromium, and other anions removal in drinking water and in liquid waste stream (IX brine or RO concentrate). In addition to arsenic removal performance, the minimization of residuals (also tested during this project) showed significant potential for reducing the spent media volume up to 20 fold for effective residual management.

Finally, a number of ideas for future research have been presented to help further demonstrate this innovative method as a viable alternative for arsenic treatment.

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).

PARTICIPANTS:

• County of Los Angeles Department of Public Works, Water Works Division, Calif.

• City of Signal Hill, Calif.

• City of Pomona, Calif.

• Irvine Ranch Water District, Calif.

• Chino Desalter Authority, Calif.