November 2009, Vol. 21, No.11

Research Notes

Research Notes - Method Shows Promise for Removing Groundwater Nitrate, Researchers Say

While it might sound like a nighttime hot spot to get drinks in Copenhagen, Nitrabar is actually a new nitrate-removal technology developed by a team of European researchers. Nitrabar filters nitrate-rich water using a permeable reactive barrier.

The system consists of a trench dug at a site where its location and depth are appropriate to intercept shallow groundwater heading for a larger waterbody, said Bruce Howard, Nitrabar project manager. The trench is filled with crushed rock and organic material, such as mulch. This creates optimal conditions, according to Howard, for bacteria naturally occurring in the ground to convert nitrate to nitrogen gas through microbial denitrification.

The Nitrabar system is designed for uses in agricultural locations where nitrate easily accumulates in groundwater and ends up in nearby rivers. Excessive amounts of nitrogen in waterbodies can cause algal blooms, resulting in “dead zones,” where little aquatic life can survive. The Nitrabar project is an endeavor to stop the flow of nitrogen at its agricultural source.

At a demonstration site operating since early 2008 in Ballymena in Northern Ireland, the Nitrabar system has achieved a reduction of more than 85% in the nitrate that flows through the barrier, Howard said. Though the demonstration ended in September, members of the international research team are taking the acquired knowledge and promoting it in their homelands across Europe.

Howard estimated that the cost of a 100-m Nitrabar trench at $1000 to $2000, making it a low-cost, decentralized solution for preventing nitrate buildups in local waters. Length and depth of the trench are variable, based on location. Howard noted that “in many cases, the mulch used may be a waste material,” furthering the environmental stewardship of the system. For more information, see www.nitrabar.eu.

Atom Substitution Improves Water Decontamination

Sandia National Laboratories has created a new compound that removes bacterial, viral, and other organic and inorganic contaminants from water.

Scientists substituted an atom in the water treatment coagulant aluminum oxide, commonly used to purify water, with an atom of gallium to create a compound that resists forming larger, less-reactive aggregates before use. This leads to a longer shelf life than that of related products, according to a Sandia news release.

The gallium atom improves stability and effectiveness of the reagent, according to Sandia principal investigator May Nyman. The coagulant attracts and binds contaminants effectively because it maintains its electrostatic charge more reliably than conventional coagulants without gallium, the news release says. “We’ve done side-by side tests with a variety of commercially available products,” Nyman said. “For almost every case, ours performs best under a wide range of conditions.”

The decontaminant is designed to clean river water before it’s treated for consumption or to clean treated wastewater before it enters the environment, according to the news release. The water treatment coagulant works best in natural systems that have fluctuations in pH, temperature, turbidity, and water chemistry, Nyman explained. These fluctuations are common in natural water sources and vary from one source to the next, the news release says.

Substituting a gallium atom for an aluminum atom was studied by collaborators at the University of California–Davis but had not been used in an application until the work at Sandia, Nyman said.

The atoms are substituted by dissolving aluminum salts in water, dissolving gallium salts into a sodium hydroxide solution, and then slowly adding the sodium hydroxide solution to the aluminum solution while heating, the news release says. Nyman and Sandia microbiologist Tom Stewart developed this patent-pending, material-based approach to purifying water and performed treatment studies at the lab, the release says. Sandia, operated by Sandia Corp., a Lockheed Martin Corp. (Bethesda, Md.) company, is exploring the commercial potential of the compound.