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Denitrification in Porous Media during Rapid, Continuous Leaching of Synthetic Wastewater at Saturated Water Flow

Dep. of Environ. Science and Eng., Faculty of Eng., Hiroshima Univ., Higashi-Hiroshima, 724 Japan;
Environ. Eng. Lab., Dep. of Civil Eng., Univ. of Aalborg, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark;
Dep. of Land, Air, and Water Resour., Univ. of California, Davis, CA 95616.

^* Corresponding author.

ABSTRACT

Increasing interest is given to land treatment and especially rapid infiltration (RI) systems as a method to remove N in wastewater by denitrification. The purpose of this article is to investigate denitrification in porous media at conditions corresponding to RI land treatment systems. Denitrification in six porous media columns (98% decomposed granite or sand and 2% field soil) during saturated leaching at constant flow rates of synthetic wastewater was investigated. Concentrations of NO₃-N and methanol between 20 and 60 mg L^–1 were applied and vertical concentration profiles of NO₃-N, NO₂-N, and NH₄-N were measured for 45 d at 30 °C (three columns) and 10 °C (three columns). A time lag in denitrification of 10 d was found at 10 °C. Complete N removal was obtained after 3 d at 30 °C but was not obtained at high N-loading at 10 °C. A NO₂-N leaching was observed between Day 1 and 3 at 30 °C. Assuming first-order denitrification at steady state, the corresponding first-order reaction rate coefficients (k₁) for NO₃ reduction in the columns were estimated to be between 1.4 and 5.0 h^–1 at 30 °C and between 0.017 and 0.14 h^–1 at 10 °C. The NO₃-N concentration in the influent found to be the most optimal for denitrification at steady state was 20 mg N L^–1 at 10 °C and 40 mg N L^–1 at 30 °C. No significant differences in k₁ values in columns containing decomposed granite and sand, respectively, were found. Steady-state NO₃ profiles were obtained between 1.5 to 4.5 wk after the experiments were started.

Contribution from Hiroshima Univ., Univ. of Aalborg, Danish Res. Academy, and Univ. of California-Davis.

Received for publication September 28, 1989.