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Effect of Sludge Additions on Nitrogen Removal in Soil Columns Flooded with Secondary Effluent¹

ABSTRACT

Mixing sewage sludge with the surface layer of soil in columns was tested as a way to increase N removal in soil columns flooded with secondary effluent containing 18 mg/L total N. Dry sludge was mixed in the top 5 cm of two columns at an application rate equivalent to 50 Mg/ha. The infiltration rates of the two columns were 30 and 60 cm/d. The infiltration rates were the same before and after addition of sludge. Nitrogen (total) removed by the 30 cm/d column was increased from about 22 to about 55% by adding sludge. The same amount of sludge added to the 60 cm/d column decreased N removal for several cycles before N removal stabilized at 34% or at about double the rate measured before sludge was added. Sludge decomposition in the soil columns apparently provided a steady source of organic C for denitrifying bacteria. Nitrogen removal at the 30 cm/d infiltration rate was sufficient to maintain the average total N content in the water from the column outlet at 8 mg/L. These results show that mixing sludge with soil in ground-water recharge basins could allow increased application rates of sewage water and thereby reduced costs. Utilization of some sludge without contaminating the groundwater would be an added benefit.

Key Words: wastewater • denitrification • NO^–₃ • sewage

¹ Contribution from the Water Quality and Watershed Research Laboratory, USDA-ARS, P.O. Box 1430, Durant, OK 74702.

² Soil Scientist.

Received for publication October 25, 1985.