Effect of Sludge Additions on Nitrogen Removal in Soil Columns Flooded with Secondary Effluent
1986
Lance, J. C.
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.
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