Denitrification in soils intermittently flooded with sewage water
1977
Lance, J.C.
Net nitrogen removal averaged 30% when soil columns were intermittently flooded with secondary sewage effluent at infiltration rates that resulted in a total annual infiltration of 85 meters of water. Most of the nitrogen remaining in the water was concentrated in a nitrate peak measured at the beginning of each flooding period. Nitrogen removal from soil columns was increased to 90% by adding 150 ppm soluble carbon as dextrose to the sewage water. Much of the added organic carbon moved through the soil columns. However, a pulse of organic carbon added at the beginning of the flooding period increased N removal to only 50 to 60%. Nitrogen removal was increased to 80% by reducing the infiltration rate from 35 to 15 cm/day. The lower infiltration rate still resulted in a total annual infiltration of 40 meters of water. The decrease in infiltration rate resulted in more mixing of the nitrate with incoming sewage water, and thus provided a more favorable C to NO₃-N ratio for denitrification. Vegetation increased nitrogen removal about 10% over a wide range of infiltration rates. Nitrogen removal was increased to 75 to 80% by collecting high-nitrate water from the columns during the first 3 days of flooding, mixing it with sewage water, and recycling it through the columns.
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