Reduction of Nitrogen Concentrations in
Swine Lagoon Effluent by Biological
Denitrification
JAMES K. KOELLIKER, Graduate Assistant
J. RONALD MINER, Assistant Professor
Department of Agricultural Engineering
Iowa State University
Ames, Iowa
INTRODUCTION
Conventional schemes that treat liquid animal wastes are designed to reduce
organic material and to reduce solids volume before final disposal. Removal of
nitrogen by such operations usually is incidental. Treatment of swine manure at Iowa
State University by anaerobic lagooning removes 89-96 per cent of the COD and
57-65 per cent of the total nitrogen (1). Total nitrogen in the lagoon effluent ranges
from 200-500 mg/1 during the year. About 90 per cent of the nitrogen is in the form
of ammonia nitrogen (NH3-N).
If such lagoon effluent were released into the environment, problems would
arise from the quantities of nitrogen remaining. If it were released to streams, the
NH3-N would be toxic to fish life, oxidation of NH3-N to nitrite and nitrate nitrogen
(NO2-N and NO3-N) would consume DO and the nitrogen would stimulate excessive
growth of aquatic plants. Also, if this high nitrogen water (after the nitrogen is
converted to NO3-N) reached drinking water supplies, human and animal health
problems might result.
Disposal of anaerobic lagoon effluent by field irrigation also causes some
problems. If the effluent is disposed of so that the nitrogen is utilized by growing
crops, only two to five in. per year should be applied to meet crop requirements and
minimize groundwater pollution potential. This type of disposal requires relatively
large land areas and a considerable investment in spreading equipment.
Approximately one acre of land would be needed for each 20 finishing swine on
feed.
Another possible method of irrigation disposal is to apply 20-50 in. of lagoon
effluent per year and reduce nitrogen by denitrification in the soil (2). The amount
of organic material in the lagoon effluent, however, is evidently too low in quantity
or not sufficiently available to denitrifying organisms to promote adequate nitrogen
reduction. Thus, soil organic matter is attacked as an organic carbon source, and,
more importantly, incomplete denitrification releases nitrogen to surface waters from
tile drainage from the disposal area or to groundwater by deep percolation.
Because of these problems, or potential problems, with irrigation disposal of
anaerobic swine lagoon effluent, we undertook a study exploring the feasibility of
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