Chemical Composition of Sewage Sludges and Analysis of Their Potential Use as Fertilizers

Abstract

A regional survey of sewage sludge composition was conducted by obtaining data for 30 constituents in > 250 sewage sludge samples from approximately 150 treatment plants located in 6 states in the north‐central region and 2 in the eastern region. Computation of the mean and median values indicated that N, P, and K levels were within a relatively narrow range, whereas these statistics demonstrated that Pb, Zn, Cu, Ni, and Cd concentrations were extremely variable. Median concentrations for anaerobically digested sewage sludges were as follows: N, 4.2; P, 3.0; K, 0.3%; Pb, 540; Zn, 1,890; Cu, 1,000; Ni, 85; and Cd, 16 mg/kg, and for aerobically treated sludges: N, 4.8; P, 2.7; K, 0.4%; Pb, 300; Zn, 1,800; Cu, 970; Ni, 31; and Cd, 16 mg/kg. Based on population and sludge production estimates, < 1% of the agricultural land would be required for application of sewage sludge at a rate of 100 kg available N per ha in most of the states considered. The heterogeneous nature of sewage sludges produced by different cities and the presence of potentially harmful trace metals necessitates a knowledge of the chemical composition of each individual sewage sludge prior to land application.