Nitrogen Removal with Aerobic Granules – Effect of Dissolved Oxygen and Carbon/Nitrogen Ratio

Abstract

Nitrogen removal efficiency related to the dissolved oxygen (DO) concentration (DO 1–7 mg l–1), carbon/nitrogen ratio (COD/N 1–14), and the effect of airflow (0.4–2.9 l min–1) related to the granule size were investigated. The average chemical oxygen demand (COD) removal of ≥ 90 % was achieved at COD/N ≥ 11, but the satisfactory N values in effluent for discharge into the surface waters were almost achieved at COD/N 14. DO of 2 mg l–1 is recommended for efficient removal of N and COD with mature granules. The size (diameter) of the granules decreases with increased airflow