AWWA WQTC57133

In October of 2001, the US Environmental Protection Agency (EPA) Administrator adopted an arsenic (As) maximum contaminant level (MCL) of 10 ppb. During the years that the MCL was under review, a number of new technologies emerged for As treatment. Many of these new technologies may work well for removal of As(V), but most fail to treat As(III). As (III) exists as a neutral species in water at the pH range typically encountered during drinking water treatment, consequently it is not readily sorbed by ion exchange. As a result, most treatment technologies require a separate oxidation step to convert As(III) to As(V). The current As(V) treatment technologies available are also limited by pH and can be costly. Studies have shown that As(III) is more toxic than As(V), hence, the removal of As(III) is important. Thus, it has become increasingly important to develop a treatment technology for the removal of both As forms, and at this time there is little data available on As(III) treatment technologies. This paper discusses the development of a medium capable of removing both As forms from drinking water. This technology is suitable for both point-of-use treatment and integration into existing water treatment plant process streams, without the addition of capital-intensive improvements. The medium is a natural zeolite coated with Mn-substituted nanophase Fe oxides (NZNPF). The NZNPF medium removes both As(III) and As(V) from contaminated waters. As(V) is removed by sorption process, whereas, As(III) is removed by a mechanism called Reductive Dissolution. In this process, Mn(III)/Mn(IV) is reduced to Mn(II) which results in oxidation of As(III) to As(V), and the release of Mn and Fe into solution. The oxidized As is sorbed by the medium and the resulting Mn and Fe are released into the solution, some of which may be re-sorbed by the medium. Thereby, the concentrations of Mn and Fe are well below the regulatory secondary limits for drinking water. Under laboratory conditions NZNPF media was able to reduce two As spiked waters (one with 54 ppb As(III) and a second with 54 ppb As(V)) to <3 ppb (below instrument detection limits). Additional testing has demonstrated the effectiveness of the medium over a wide pH range from 4 to 9. This medium is currently undergoing pilot-scale studies to verify the long-term exchange capacities. Toxicity characteristics leaching procedure (TCLP) testing has determined that the NZNPF medium can be disposed of easily (non-hazardous waste). The ease of disposal and low cost of the medium makes it attractive for use in filtration beds, pressurized vessels or added directly to the existing coagulation process at water treatment plants. Includes 10 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2002

Number of Pages:

15

File Size:

1 file , 350 KB