Removal of Arsenic From Drinking Water Using a Novel Hybrid Sorbent

VEETech, in conjunction with Lehigh University, will synthesize and test novel hybrid sorbents (HIXs) for the removal of arsenic from drinking water. The HIXs are polymeric/inorganic hybrid sorbents in which cation exchange resin beads are irreversibly and uniformly coated with hydrated ferric oxide (HFO) materials. The HIXs are expected to demonstrate superior selectivity and capacity over other exchange materials used for removal of arsenic contaminants. Unlike other treatment processes, the HIXs do not require any pre- or post-treatment, and they are not expected to alter the quality of the treated water.

This project will entail the synthesis of three different HIXs and determine their relative distribution coefficients (Kd) for the arsenic species. The HIX medium exhibiting the highest Kd will be selected for kinetic testing. Following the kinetic testing, the HIX will be utilized to perform a dynamic column test to determine bed breakthrough. Following the bed breakthrough, regeneration and rinsing tests will be performed to determine the long-term bed usage and to ascertain the potential cost for the treatment approach. Finally, a detailed test report will be prepared to describe and document the entire test protocol with results and future activities.

Arsenic poisoning from drinking water is a major global concern. In the United States, there currently are several drinking water supply systems that frequently exceed the 60-year-old arsenic maximum concentration limit (MCL) of 50 ¿g/L. In the coming years, the MCL for arsenic is expected to be lowered to 10 ¿g/L, a level that is more consistent with other developed nations. Arsenic is found in the drinking water systems as both III and V species. The arsenic III forms are non-ionic and remain oxyacids, while the V forms remain oxyanions. Both forms are acutely toxic to all warm-blooded, living beings.

Arsenic can be removed from drinking water in the following ways:

¿ Activated alumina sorption
¿ Polymeric anion exchange
¿ Sorption by ion oxide-coated sand and zeolite particles
¿ Enhanced coagulation with alum or ferric chloride followed by microfiltration
¿ Pressurized granular ion particles and iron-doped alginate
¿ Manganese dioxide-coated sand
¿ Polymeric ligand exchange
¿ Zero valent iron.

Each of the above technologies has relative advantages and disadvantages, but all of them have a few major drawbacks, such as:

¿ Limited capacity¿the capacity of the technologies are limited in terms of feed throughput or bed volumes.
¿ Lack of selectivity¿the technologies are not particularly selective for the two forms of arsenic species and may prefer to treat other competing ions.
¿ Requirement for pre- and post-treatment¿the treated water often requires pre- and post-treatment (in the forms of chemical addition) to maintain water quality.
¿ Non-removable arsenic III species¿the arsenic III oxyacids are not removed by the technologies, thus providing an incomplete arsenic removal.
¿ Expense¿they are relatively expensive to operate.

The HIXs developed from this study alleviate all of the drawbacks listed above. The HIXs are prepared by uniformly coating cation exchange polymer beads with HFO. The HIX can be used in a fixed-bed sorption exchanger and can treat the water for numerous bed columns. The HIX is extremely selective for both forms (III and V) of arsenic species and does not capture the competing ions. The HIX beds do not alternate water quality, and no pre- or post-treatment is required. The HIX fixed-bed technologies are extremely cost-effective and easy to operate and maintain.

Commercialization of the HIX-based fixed-bed arsenic removal technologies can benefit the numerous drinking water utilities affected by arsenic concentrations in excess of the MCL. The technology can be configured as a permanent or mobile system. The basic components are one or two columns and a small number of tanks and pumps. The HIX system also can be retrofitted as a polishing unit downstream of the existing water distribution system. The technology also has very good export potential to the countries suffering from acute arsenic toxicity.