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 NO_x-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 NO_x-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 NO_x-N m⁻³ h⁻¹, respectively. The rate of 27.8 g NO_x-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.

Keywords:

• Denitrification
• filter
• filtration
• wastewater
• reaction order
• reaction rate constant
• suspended solids removal

Acknowledgments

Valuable support and help in the preparation of the manuscript by Elzbieta Plaza is greatly appreciated. Eva Hagland helped to a great extent with the VKI tests. Bengt Carlsson at the University of Uppsala helped to a great extent with the Maple computer program. Many ideas and support during the time of experimentation was given by Lars-Gunnar Reinius.

Additional information

Funding

This work was supported by Stockholm Water Co. and NUTEK (within the STAMP project).