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Evaluation of a Sulfur-Thiobacillus denitrificans Nitrate Removal System¹

ABSTRACT

An evaluation of sulfur-Thiobacillus denitrificans nitrate removal system as a means of denitrifying nitrified septic tank effluent was conducted. Duplicate 10 by 64 cm columns were filled with a 1/1 mixture (wt/wt) of elemental S (>2 mm) and dolomite chips (1 cm), and were pretreated by recycling an enrichment culture of T. denitrificans ATCC 23642 through the columns for 3 days. Continuous passage of the nitrified septic tank effluent (column influent) containing 40 µg NO₃^–-N/ml through the columns resulted in nearly complete NO₃^– removal in 3.3 hours at steady-state conditions (23C). Statistical analyses indicated that the denitrification kinetics closely resemble first order in the range of NO₃^– concentrations employed. Oxidation-reduction potentials (Pt black electrodes) ranged from +160 to +300 mV. Analysis the gases produced showed that N₂ was present in highest concentration. Sulfate was the major S end product and was present at relatively high concentrations (90 µg SO₄^2–-S/ml). A significant decrease in inorganic C occurred with depth in the columns while changes in organic C content were insignificant. A significant linear relationship was obtained between decreases in (NO₃^– + NO₂^–)-N and production of S0₄^2–-S. Passage of column effluent through 10 by 60 cm Plainfield sand columns did not significantly decrease SO₄^2– levels. While use of this NO₃^– removal system appears promising, SO₄^2– contamination of the ground water may limit its applicability.

Key Words: first order kinetics • oxidation-reduction potentials • gas analysis • sulfate • denitrification

¹ Research supported by the Coll. of Agric. and Life Sci., Univ. of Wisconsin, Madison, WI 53706, and by the Small Scale Waste Manage. Proj. funded by the State of Wisconsin and U. S. Environ. Prot. Agency, Grant No. 144G065.

² Research Associate and Professor, respectively, Dep. of Soil Sci., Univ. of Wis. The senior author is now with the USDA-ARS, Agric. Environ. Qual. Inst., Biol. Waste Manage. and Soil N Lab., Beltsville, MD 20705.

Received for publication October 9, 1975.