Groundwater Biodenitrification on Sand Fixed Film Reactor Using Sugars as Organic Carbon Source

Results of a biological denitrification demonstration plant for drinking water, operated for about two years under different conditions, are here summarized. The fixed film anoxic reactor worked downflow at flowrates up to 20 m³/h, using a groundwater with quite variable NO₃ concentration (32-52.5 mg NO₃/L); thus, nitrate volumetric load C_v range was 0.40-1.45 kg NO₃-N/m³ of active bed per day (1.8-6.5 kg NO₃/m³·day). These figures were obtained with varied flow (and related hydraulic contact time HCT), partial recirculation of treated water and NO₃ addition (fixed HCT); for a short period C_v reached 1.95 kg NO₃-N/m³·d, for both NO₃ extradosing and flowrate increase. Nitrogen removal rates, using sugar or glucose syrup as organic carbon sources for heterotrophic denitrification, were usually above 80% for the whole biological section (taking into account NO₂ oxidation), but NO₃ removal rate in the anoxic reactor often reached 95%. For different operating conditions, both substrates gave comparable results, requiring a quite low degree of post-treatments. Heterotrophic denitrification using sugars seems to be a practicable way to solve the problem of increasing NO₃ concentrations in drinking water.