By Henry G. Nowicki, Ph.D.
A number of facets of the controversial arsenic issue were covered at the NSF International symposium in Washington, D.C., in late April. Attendees had opportunities to hear cutting edge talks on treatment technologies and view posters presentations on measurement technologies and operator certification programs.
A hot topic
Potential benefits to the point-of-use/point-of-entry (POU/POE) marketplace in the arsenic debate loom largely. The general public knows about arsenic as a toxin in murder mysteries in books and on TV. In the last several months, though, arsenic in drinking water was continuously in the national spotlight. The March implementation delay of the U.S. Environmental Protection Agency (USEPA) Arsenic Rule drew national media coverage, as the Bush Administration reconsiders whether the standard should be set at 10 parts per billion (ppb) or higher. This can only help manufacturers and marketers of POU/POE devices. Political aspects of the ongoing arsenic story may draw needed attention and dollars to the industry.
Since 1942, the arsenic maximum contaminant level (MCL) in U.S. drinking water has been 50 ppb. Congress ordered the USEPA to set a new standard in 1996 when the Safe Drinking Water Act was reauthorized. In January, the outgoing Clinton Administration made a last-minute ruling to set the new MCL at 10 ppb. But it was challenged in court by Western utilities and mining interests as too costly and new USEPA administrator Christine Todd Whitman revoked it. Acknowledging the current MCL is too high, she initiated an accelerated study to reevaluate the determination. A nine-member committee of experts was appointed in May to look at how far it should be lowered. A day later, the Natural Resources Defense Council sued the Administration over the delay. Regardless, a 1998 USEPA ruling allows municipal water suppliers to help their customers select POU purification devices—again, this should help POU/POE suppliers.
Environmentalists stress the scientific evidence about the health effects of arsenic in drinking water is clear. A 1999 report by the National Academy of Sciences concluded that the current USEPA limit on arsenic doesn’t achieve the agency’s goal for health protection. Meanwhile, both the European Union and the World Health Organization have adopted a 10 ppb standard for arsenic in drinking water—the WHO in 1993.
Thomas Sorg, P.E., of the USEPA’s National Risk Management Research Laboratory in Cincinnati, chaired the arsenic section. Leading scientists presented a wide variety of information about treatment technologies for arsenic removal and measurements. Many speakers pointed out that one technology will probably not fit all raw water supplies. Most treatment technologies performance depends on water parameters such as pH, arsenic species (As+3 and As+5), concentration of iron and manganese in raw water, total solids (suspended and soluble), natural organic matter (NOM), and competing anions (nitrate/nitrite, perchlorate, chloride, fluoride and especially sulfate and phosphate). Technologies discussed at the conference included physical-chemical processes, ion exchange, reverse osmosis (RO), iron and aluminum oxide based materials, zeolites, greensand and activated carbon. Information also was presented on bioremediation of arsenic in soil with a specific fern species that absorbs it through its root system.
Strengths & weaknesses
There are strengths and weaknesses for each technology, and only the major points are presented here. As+5 (arsenate) is easier to remove than As+3 (arsenite) with all technologies. Many speakers pointed out that strong oxidizers like chlorine, potassium permanganate or ozone are needed to provide efficient oxidation. RO seems to have a niche for waters with high sulfate, or other high concentrations of competing anions. Ion exchange seems to have strength with clean waters that have only arsenic as a significant problem. Zeolites infused with ferrous iron have enhanced performance. Alumina and iron oxides seem to have the broadest application for drinking waters. Alumina needs water with a pH of 5.5-6.5 to perform optimally; thus, pre- and post-pH adjustments are needed to maximize activated alumina oxide performance. Iron oxide based materials have a broad pH range for maximized performance. Therefore, iron oxide filters don’t need pre- and post-filter pH adjustments. Also, iron oxides seem to perform equally well with arsenite and arsenate when compared to the other technologies, which have a preference for arsenate; however, iron oxide based filters need high pressure operating equipment (which have cost and potential operational problems) due to its physical properties.
The arsenic subject should be fertile for the coming decade. Many scientists have good treatment ideas. It’s only a matter of time until the best ideas are made commercially successful. A transcript of the conference’s proceedings may be purchased from NSF.
About the author
Dr. Henry G. Nowicki is president of PACS Inc. in Pittsburgh, PA, which offers a variety of laboratory, training and consulting services as well as sponsors the International Activated Carbon Conference (IACC). He also is a member of the WC&P Technical Review Committee. Nowicki can be reached at (724) 457-6576 or email: email@example.com.