Iowa Agriculture and Home Economics Experiment Station Research Bulletin


Knowledge of the chemical composition of sewage sludges produced by wastewater treatment plants in Iowa is essential for future attempts to recycle this material on agricultural land. Sewage sludges produced by treatment plants in 44 Iowa communities, ranging in population from < 1,000 to >50,000, were analyzed for 30 constituents to survey the quality of the sludges and to assess the potential of this material as a source of plant nutrients for crop production in this region. Results showed that, expressed on an oven-dry basis, the median values of organic C, and total N, P, K, and S were 31, 2.6,1.2, 0.3, and 1.1%, respectively, and that the median values for Ca, Mg, Na, and Fe were 7.0, 0.7, 0.2, and 2.0%. Expressed in ppm (m g/kg) of oven-dried sludge in parentheses, the median values for the heavy metals and other trace elements 3 were: Ag(10), As(173), B(100), Be (<0.25), Cd(25), Co(23), Cr(138), Cu(300), Hg(1.3), Mn(319), Mo(13), Ni(28), Pb(250), Se(<25), SK <4), V(26), and Zn(l,H 3). Based on population and sewage sludge estimates, < 0.4% of the cropland in Iowa would be required for application of the sewage sludges produced if applied at a rate of 100 kg available N per ha. The variable nature of sewage sludges produced by different communities in Iowa and the presence of potentially harmful amounts of heavy metals in most of the samples analyzed indicate that the chemical composition of every sewage sludge should be known before its application to agricultural land.



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