Organic carbon and nitrogen removal from a strong wastewater using a denitrifying suspended growth reactor and a horizontal-flow biofilm reactor

Recirculation of fully nitrified effluent from a laboratory horizontal-flow biofilm reactor (HFBR) to a mixed pre-denitrification reactor (DR) was used to remove organic carbon and nitrogen from synthetic dairy wastewater. Three recirculation ratios of 2, 4, and 6 were examined in this study and the average filtered chemical oxygen demand (CODf) and total nitrogen (TN) removals were up to 97.4% and 85.5%, respectively, at 11 °C. In the DR, the nitrate nitrogen removal efficiencies and rates were 86–96% and 22–34 g N/m3 d. In the HFBR, the ammonium nitrogen removal rates were 293–337 mg N/m2 d.