Efficiency and detrimental side effects of denitrifying bioreactors for nitrate reduction in drainage water
2015
Weigelhofer, Gabriele | Hein, Thomas
A laboratory column experiment was conducted to test the efficiency of denitrifying bioreactors for the nitrate (NO₃-N) removal in drainage waters at different flow rates and after desiccation. In addition, we investigated detrimental side effects in terms of the release of nitrite (NO₂-N), ammonium (NH₄-N), phosphate (PO₄-P), dissolved organic carbon (DOC), methane (CH₄), and dinitrogen oxide (N₂O). The NO₃-N removal efficiency decreased with increasing NO₃-N concentrations, increasing flow rates, and after desiccation. Bioreactors with purely organic fillings showed higher NO₃-N removal rates (42.6–55.7 g NO₃-N m⁻³ day⁻¹) than those with organic and inorganic fillings (6.5–21.4 g NO₃-N m⁻³ day⁻¹). The release of NO₂-N and DOC was considerable and resulted in concentrations of up to 800 μg NO₂-N L⁻¹and 25 mg DOC L⁻¹ in the effluent water. N₂O concentrations increased by 4.0 to 15.3 μg N₂O-N L⁻¹ between the influent and the effluent, while CH₄ production rates were low. Our study confirms the high potential of denitrifying bioreactors to mitigate NO₃-N pollution in drainage waters, but highlights also the potential risks for the environment.
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