Denitrification process and suspended solids separation in deep-bed two-media down-flow filters

Abstract

A denitrification process with simultaneous suspended solids separation and denitrification was studied in pilot-scale filters. Denitrification rates for the total, upper, middle, and lower layer of the filter bed were 21.3, 79.0, 27.8, and 21.9 g (NO3+NO2)-N m−3 filter bed h−1 (g NOx-N m−3 h−1), respectively. The biofilm on the grains showed denitrification rates for not backwashed grains and grains backwashed once of 8.8 and 7.8 g NOx-N m−3 h−1, respectively, indicating a robust biofilm. Construction and operation strategies of full-scale filters were done based on the pilot-scale study results. For further optimization of the denitrification process, 1 of 60 filters in operation was chosen for a full-scale study. The denitrification rates for the total layer, upper layer, middle layers, and lower layer of the filter bed were 12.7, 15.6, 27.3, 27.9, 27.8, and 14.0 g NOx-N m−3 h−1, respectively. The rate of 27.8 g NOx-N m−3 h−1 was obtained for a middle layer in both filters. The amount of nitrogen possible to reduce in the full-scale filters was calculated to 8.8 mg N L−1 or 2403 kg N d−1. This paper presents results of denitrification rates, reaction orders, rate constants, and suspended solids separation.