Until recently, the general view was that in soils, optimal denitrification rates occur at pH 7-8, that the ratio of denitrification products N2O/N2 decreases as the pH is raised, and that N2O produced in acid soils is more likely a product of heterotrophic nitrification rather than denitrification. However, new studies have shown that microorganisms can denitrify in acid soils, can adapt to acid soil conditions, and that microbial pH optima are similar to the pH of soils. Also, in aquatic systems, a high denitrification potential was observed for acid mine sediments from several affected streams ranging from pH 2.6 to 4.9 in Colorado, US.
In contrast to the above, various reports have demonstrated that NO3 concentrations can be reduced most efficiently at higher pH in effluent treatment works. In one study, denitrification of synthetic wastewater with a high NO3 concentration was inhibited at pH values below 7, but complete denitrification occurred from pH 7.5 to 9.0.
The process of denitrification increases the pH of its surrounding environment, which can be beneficial for some aquatic systems. The buildup of high NO3 concentrations in a closed seawater aquarium was minimized by installing a biological denitrification system. In addition, this system offers additional benefits by increasing the pH and alkalinity ofseawater and providing a reducing environment to balance the oxidizing disinfection environment in the aquarium.
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