The Oulu-based environmental technology company Envitop Oy has developed a new method for the denitrification of waste water. The innovation is based on the use of a reactive filter as a bioreactor.

Denitrification at waste water treatment plants is a difficult task in Finnish conditions because the traditional microbiological treatment method operates reliably only at a water temperature of + 12 OC. Envitop's reactive filter offers a solution to the problem: it operates during all seasons of the year and the degree of treatment achieved with it can also be controlled in real time.

In the method developed by Envitop since 1998 the ammonium nitrate in water leaving a waste water treatment plant is bound to a reactive filter in which it is oxidized into a concentrated nitrate solution.

"This solution is added to the sewerage network where the nitrate is reduced to a harmless and odourless nitrogen gas, at the same time reducing offensive smells in the sewerage network," says Jukka Palko, the managing director.

Not much space needed

Although the conditions for a permit for treating waste water do not yet make denitrification an obligation, in the most modern treatment plants in the big cities denitrification is already part of the treatment process. One advantage of Envitop's method is the limited space it requires, less than a third compared with the traditional microbiological denitrification.

"The small space leads on to a reduced need for water aeration, which reduces operating costs," Palko says.

Envitop, which specializes in soil chemistry and hydrochemistry, is the market leader in Finland as a supplier of rapid tests and reactive filter materials. With its co-partners the company disposes of between 150,000 and 300,000 tonnes of seriously contaminated soil and hazardous waste.

>> www.envitop.com

The reactive filter developed by Envitop eliminates the nitrogen in waste water during all seasons of the year.