Nitrates in Soils and Waters from Sewage Wastes on Land

Abstract

Research was initiated in 1973 at St. Paul, Minnesota, with objectives to develop efficient, practical, and environmentally safe methods for utilizing sewage wastes on land in harmony with agricultural usage. Applications of municipal sewage sludge and/or wastewater effluent were studied. Liquid digested sewage sludges from several wastewater treatment plants were applied to a 16-ha terraced watershed cropped to maize ( Zea mays L.) and reed canarygrass ( Phalaris arundinacea L.). The sludge was transported to the site by tank truck, stored in lagoons, and spread by combinations of traveling gun and subsurface injection. Sludge was applied to the maize areas for 20 years (total of 68 cm, 224 tonnes ha −1 solids, and 9460 kg ha −1 total N) and to the reed canarygrass areas for 12 years (total of 96 cm, 173 tonnes ha −1 solids, and 10 040 kg ha −1 total N). Crop yields were high with normal plant tissue concentrations of N, P, and K. Analysis of water samples from runoff, soil, and ground water showed no movement of potentially polluting materials out of the watershed via surface runoff or leaching. Wastewater effluent was sprinkled onto a 2-ha area containing maize and eight forage species for a four-year period at about 5 and 10 cm wk −1 (total of 120 to 280 cm yr −1 and 260 to 680 kg N ha −1 yr −1 ). Tile drainage, ground and soil water, soils, and crops were analyzed for N, P, K, and trace metals. Maize and forage grasses produced high yields (average of 13.4 and 11.1 tonnes ha −1 for maize and reed canarygrass, respectively). Removal of N and P from effluent by the combination of crop uptake and soil sorption was satisfactory. No increase in trace metal concentrations was detected in either the water percolate or crops. Special management of the crop was important for maintaining adequate infiltration rates, for producing high yields of dry matter, and for maximum removal of N.