Scientists test new nitrate-removing reactor

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Scientists have tested a novel technique for removing high levels of nitrate from water in public aquariums using a new type of biological and chemical filter system.

The team of experts from Portugal tested the ion exchange membrane bio-reactor, or IEMB, at the Oceanario de Lisboa public aquarium, and saw it reduce nitrate levels from 251 and 380 mg/l to below 27 mg/l.

The IEMB was able to remove the naturally accumulated nitrate in the aquarium's water, by bioconverting it to nitrogen gas within an isolated "bio-compartment", without contaminating the water with anaerobic bacteria or the ethanol added to the unit as a carbon source for the microbes.

One drawback of the system is that it works, in part, by exchanging nitrate ions for chloride ions, so it does affect the overall composition of the water, despite removing pollutants.

The authors said: "Under the studied operating conditions, the IEMB proves to be a selective nitrate removing technology preserving the initial water composition with respect to cations, due to the Donnan exclusion effect from the membrane, and minimizing the counter diffusion of anions other than nitrate and chloride, due to the use of water with the same ionic composition in the bio-compartment.

"This is an advantage of the IEMB concept, since the quality of the water produced would allow for the re-utilisation of the treated water in the aquarium, thereby reducing both the waste water volume and the use of fresh water."

For more information see the paper: Matos CT, Sequeira AM, Velizarov S, Crespo JG, Reis MA (2009) - Nitrate removal in a closed marine system through the ion exchange membrane bioreactor. J Hazard Mater. 2008 Nov 21.